g
LightSpeed 4.X
LightSpeed 16
Technical Reference Manual
CE 0459
Operator Reference
Direction 2351785-100
Rev 7 (07/05)
Copyright, 2005 by GE Healthcare
GE Healthcare
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Table of Contents
REVISION HISTORY .............................................................................................................. i-1
LIST OF EFFECTIVE PAGES ................................................................................................ i-2
Chapter 1: BEFORE YOU START
User Information Description ........................................................................................ 1-2
Applications Help ................................................................................................................ 1-2
Chapter 2: X-RAY PROTECTION
Chapter 3: CT SAFETY
General Safety ...................................................................................................................... 3-2
Operator Console Ergonomics ...................................................................................... 3-2
Posture............................................................................................................................... 3-2
Equipment Adjustments ............................................................................................ 3-2
Electrical Safety ................................................................................................................... 3-4
Regulatory Requirements ............................................................................................... 3-4
Electromagnetic Compatibility (EMC) ........................................................................ 3-5
EMI/EMC Glossary Terms: ............................................................................................... 3-6
Emergency Stop .................................................................................................................. 3-7
All Systems....................................................................................................................... 3-7
Emergency Power Shutdown ........................................................................................ 3-8
Emergency Patient Care During X-Ray ON:..................................................... 3-8
Restore System After Emergency Stop .................................................................... 3-8
Systems With Gantry Control Panels.................................................................. 3-8
Restore System Emergency OFF ................................................................................. 3-9
Systems With Gantry Control Panels Only....................................................... 3-9
Radiation Safety .................................................................................................................. 3-9
SmartStep Safety ................................................................................................................ 3-10
Table Float .............................................................................................................................. 3-10
SmartStep Scanning .......................................................................................................... 3-10
Mechanical Safety .............................................................................................................. 3-11
IV Pole Safety ........................................................................................................................ 3-13
Table Tray Safety.......................................................................................................... 3-13
Systems With Metal-Free Cradles and Accessories..................................... 3-13
If the Cradle Fails to Advance: ................................................................................ 3-14
Laser Safety: Warning Labels ...................................................................................... 3-15
Operator Console ................................................................................................................ 3-16
Location of Emergency Stop................................................................................... 3-16
Gantry and Table ................................................................................................................ 3-18
Location of Emergency Stop................................................................................... 3-18
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Prepare the Cradle/Patient ............................................................................................. 3-18
Prepare the Cradle ....................................................................................................... 3-18
Prepare the Patient...................................................................................................... 3-18
Helical Safety ........................................................................................................................ 3-19
Cardiac Imaging Safety ................................................................................................... 3-20
Accuracy of Measurements ........................................................................................... 3-21
Reformat Plane Thickness ............................................................................................... 3-22
Lung Algorithm ..................................................................................................................... 3-23
Chapter 4: ACCESSING THE LEARNING AND REFERENCE GUIDE
Chapter 5: TUBE WARMUP
Chapter 6: DAILY FAST CAL PROCEDURE
Chapter 7: PREPARE THE SYSTEM
Chapter 8: CHECK DISK SPACE
Check Image Space ........................................................................................................... 8-1
Chapter 9: RESET THE SYSTEM
System Shutdown/Reset Procedures ........................................................................ 9-1
Chapter 10: STOP/START THE OPERATING SYSTEM
Octane Based Systems............................................................................................. 10-1
PC Based System.......................................................................................................... 10-2
If You Turn OFF the MDC at the End of the Scan Day:................................. 10-3
Systems with Gantry Control Panels:.................................................................. 10-3
Chapter 11: General Information
System components: .................................................................................................. 11-1
Emergency Stop:........................................................................................................... 11-1
Intended Use ......................................................................................................................... 11-1
CT Description ....................................................................................................................... 11-2
CT Operation Theory .......................................................................................................... 11-2
DICOM Print ............................................................................................................................ 11-2
X-Ray ......................................................................................................................................... 11-3
Tube Warmup ...................................................................................................................... 11-3
LightSpeed 4.X Theory of Operation .......................................................................... 11-3
System Overview .......................................................................................................... 11-3
System Characteristics .............................................................................................. 11-4
Tube .................................................................................................................................... 11-4
Detector............................................................................................................................. 11-4
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© 2005 General Electric Company. All rights reserved.
Scalable Data Acquisition Sub-System (MDAS) .............................................. 11-5
Patient Scanning........................................................................................................... 11-5
EMI/EMC ............................................................................................................................ 11-5
Network ................................................................................................................................... 11-6
Remote Host Parameters ......................................................................................... 11-6
Network Compatibility ............................................................................................... 11-7
System Data and Control Flow ..................................................................................... 11-9
X-ray Generation and Detection Details .................................................................. 11-10
Overview ........................................................................................................................... 11-10
Gantry Coordinate System ...................................................................................... 11-10
Components.................................................................................................................... 11-11
CAM Collimator .............................................................................................................. 11-11
Z-Axis Cell Summation ............................................................................................... 11-12
Collimator Theory......................................................................................................... 11-12
AutomA Theory .................................................................................................................... 11-13
AutomA Theory.............................................................................................................. 11-14
Understanding AutomA Behavior......................................................................... 11-15
System Operational Modes ............................................................................................ 11-17
Overview ........................................................................................................................... 11-17
Scout................................................................................................................................... 11-17
Pediatric Imaging.......................................................................................................... 11-17
Axial..................................................................................................................................... 11-18
Helical................................................................................................................................. 11-18
Calibration Modes ........................................................................................................ 11-20
System Image Quality Features .................................................................................. 11-20
“Lite” Geometry ............................................................................................................. 11-20
Clever Gain....................................................................................................................... 11-21
Scan and Recon Prescription User Interface (UIF)......................................... 11-21
Current X-Ray Tube Capacity Effects Prescriptions
and Interscan Delays .................................................................................................... 11-21
Focal Spot .............................................................................................................................. 11-22
Filament Selection ............................................................................................................. 11-22
Filament Selection Table .................................................................................................. 11-22
Data Collection ..................................................................................................................... 11-22
Scan Parameters .......................................................................................................... 11-23
Reconstruction ..................................................................................................................... 11-24
Helical Scan Data Usage ................................................................................................. 11-24
Channel Utilization Table - Full Modes ...................................................................... 11-25
Channel Utilization Table - Plus Modes ..................................................................... 11-25
Nominal Helical Slice Thickness............................................................................. 11-26
Slice Thickness Table — Full Modes ............................................................................ 11-26
Slice Thickness Table — Plus Modes ........................................................................... 11-27
Cardiac Helical Slice Profiles .......................................................................................... 11-27
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Calibration Scans ............................................................................................................... 11-28
Warm-up Required ............................................................................................................. 11-28
Data Storage ......................................................................................................................... 11-28
Image Display ....................................................................................................................... 11-29
Gray Scale .............................................................................................................................. 11-29
CT Number ............................................................................................................................. 11-30
Variables You Cannot Control ...................................................................................... 11-31
Pixels ......................................................................................................................................... 11-31
Pixel Coordinates ................................................................................................................ 11-31
RAS Coordinates .................................................................................................................. 11-32
Pixels and CT Numbers .................................................................................................... 11-34
Window Width ...................................................................................................................... 11-35
Window Level ........................................................................................................................ 11-35
Chapter 12: QUALITY ASSURANCE
QA Phantom ........................................................................................................................... 12-1
QA Schedule .................................................................................................................... 12-3
System Performance .................................................................................................. 12-4
High Contrast Spatial Resolution........................................................................... 12-8
MTF (optional).................................................................................................................. 12-9
Noise and Uniformity.................................................................................................. 12-11
Alignment Light Accuracy (Crucial During Biopsies) ................................... 12-14
Prescribe the QA Series for Alignment Light Accuracy
- Phantom Section #1.............................................................................................. 12-15
Typical Results and Allowable Variations.......................................................... 12-17
DOSIMETRY ............................................................................................................................. 12-20
General Information .................................................................................................... 12-20
CTDI ..................................................................................................................................... 12-21
CTDIw ................................................................................................................................... 12-24
CTDI100 Typical Technique ....................................................................................... 12-25
Other Dosimetry Information ........................................................................................ 12-28
DLP....................................................................................................................................... 12-28
Dose Efficiency .............................................................................................................. 12-29
Scout Dose ....................................................................................................................... 12-29
Phantoms for Performance Testing ........................................................................... 12-29
Noise ................................................................................................................................... 12-29
Noise ................................................................................................................................... 12-30
Nominal Slice Thickness ............................................................................................ 12-30
Sensitivity Profile........................................................................................................... 12-30
Modulation Transfer Function (MTF) ........................................................................... 12-34
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Maximum Deviation ........................................................................................................... 12-35
Typical Dose 1020.33 (C) (2) i, ii and iii................................................................. 12-35
Dose Profile 1020.33 (C) (2) iv................................................................................... 12-35
Performance 1020.33 (C) (3)..................................................................................... 12-36
Radiation Protection .......................................................................................................... 12-36
Chapter 13: Performix Ultra X-Ray Tube Specifications
Environmental Specifications ........................................................................................ 13-1
Non-Operating Environment................................................................................... 13-1
Operating Environment ............................................................................................. 13-1
Diagnostic Source Assembly ......................................................................................... 13-2
Leakage Technique Factors .................................................................................... 13-2
Quality Equivalent Filtration .................................................................................... 13-2
CT Scan Ratings ................................................................................................................... 13-2
Performix Ultra Tube Assembly .................................................................................... 13-3
Marking.............................................................................................................................. 13-3
Reference Axis................................................................................................................ 13-3
Maximum Potential Difference............................................................................... 13-3
Principle Dimensions (with mounting bracket) ............................................... 13-4
Weight (without mounting bracket) ..................................................................... 13-4
Performix Ultra Tube Insert ............................................................................................ 13-4
Target Material............................................................................................................... 13-4
Maximum Potential Difference............................................................................... 13-4
Dual Focal Spots: .......................................................................................................... 13-4
Target Angle.................................................................................................................... 13-4
Rotor Speed..................................................................................................................... 13-4
Anode Heat Capacity.................................................................................................. 13-5
Serial Exposure Rating ............................................................................................... 13-5
Single Exposure Load Rating................................................................................... 13-6
Performix Ultra Tube Assembly .................................................................................... 13-8
Maximum Heat Capacity.......................................................................................... 13-9
Maximum Tube Assembly Heat Dissipation .................................................... 13-9
Focal Spot Modulation Transfer Function......................................................... 13-9
Chapter 14: System Specifications
Helical High-Contrast Spatial Resolution ................................................................. 14-2
Axial High-Contrast Spatial Resolution ..................................................................... 14-3
Helical Low-Contrast Detectability - Statistical .................................................... 14-3
Axial Low-Contrast Detectability - Statistical ........................................................ 14-4
Helical Image Noise:.................................................................................................... 14-5
Axial Image Noise:........................................................................................................ 14-5
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LightSpeed ™ 4.X
Dose Performance .............................................................................................................. 14-6
Helical Dose..................................................................................................................... 14-6
Axial Dose......................................................................................................................... 14-6
Volumetric Helical Scan Image Quality .................................................................... 14-7
1. Visual Measurement............................................................................................... 14-7
2. Statistic Measurement .......................................................................................... 14-7
Subsystem Specifications ............................................................................................... 14-8
Host Computer............................................................................................................... 14-8
Table ................................................................................................................................... 14-10
Gantry ................................................................................................................................ 14-10
X-Ray Tube ...................................................................................................................... 14-11
Heat Storage................................................................................................................... 14-11
Dual Focal Spots............................................................................................................ 14-11
Anode ................................................................................................................................. 14-11
Laser Alignment Lights............................................................................................... 14-12
Generator Subsystem Specifications ........................................................................ 14-12
Main Power Supply ...................................................................................................... 14-12
Generator Rating and Duty Cycle......................................................................... 14-12
kV, mA, and Time Accuracy ............................................................................................ 14-13
Kilovolts ............................................................................................................................. 14-13
Milliamperes .................................................................................................................... 14-13
Exposure Time................................................................................................................ 14-14
Measuring Tool Variance .......................................................................................... 14-14
Accuracy Subject to Following Conditions ....................................................... 14-14
Measurement Basis ............................................................................................................ 14-15
Kilovolts ............................................................................................................................. 14-15
Milliamperes .................................................................................................................... 14-15
Exposure Time................................................................................................................ 14-16
Environmental Specifications ........................................................................................ 14-16
System Cooling Requirements ............................................................................... 14-16
Temperature and Humidity Specifications....................................................... 14-17
Ambient Temperature ................................................................................................ 14-17
Scan Room....................................................................................................................... 14-17
Table and Gantry In Exam Room (when room is unoccupied)............... 14-17
Media (disks/tapes) ..................................................................................................... 14-18
Relative Humidity (All Areas) ................................................................................... 14-18
Electromagnetic Interference ................................................................................. 14-18
Pollution............................................................................................................................. 14-18
Lighting.............................................................................................................................. 14-19
Altitude............................................................................................................................... 14-19
Chapter 15: Planned Maintenance
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© 2005 General Electric Company. All rights reserved.
REVISION HISTORY
REV
DATE
REASON FOR CHANGE
0
08-02
First Release for LightSpeed 4.X
1
09-02
Additional information
2
10-02
Updated information
3
11-01
Updated information
4
04-03
Updated information
5
11-03
Updated information
6
04-04
Updated information
7
07-05
WEEE Rules
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LIST OF EFFECTIVE PAGES
PAGE
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© 2005 General Electric Company. All rights reserved.
BEFORE YOU START
Chapter 1
BEFORE YOU START
Anyone who operates this system should have received prior training before they attempt
to scan or diagnose patients. This training should include medical and X-Ray education, in
addition to GE applications training. This guide does not provide medical explanations, but it
does suggest potential applications for some of the software features. It describes potential
Safety problems, and how to avoid them.
Everyone who uses this equipment must read and understand all instructions, precautions
and warnings. This manual should be kept near the equipment. Procedures and safety
precautions should be viewed periodically.
This Guide addresses three safety classifications:
DANGER:
The most severe label describes conditions or actions which result in a specific
hazard. You will cause severe or fatal personal injury, or substantial property
damage, if you ignore these instructions.
WARNING: This label identifies conditions or actions for which result in a specific hazard.
You may cause severe personal injury, or substantial property damage, if you
ignore these instructions.
CAUTION:
This label applies to conditions or actions that have potential hazard. You can
cause minor injury or property damage if you ignore these instructions.
Various parts of your system will have the
icon. This icon on the equipment indicates
that the user manual contains additional information and should be consulted
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© 2005 General Electric Company. All rights reserved.
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LightSpeed ™ 4.X
This Manual uses pictures, or icons, to reinforce the printed message. It uses the
corresponding international symbol or icon next to the danger, warning or caution message.
For example, the upright hand with the lightning bolt across it warns of electrical hazards.
Federal law restricts this device to sale by or on the order of a physician.
Do not use the equipment if a known safety problem exists. Call your local service
provider and have the system repaired.
User Information Description
We have divided the current User Information into two parts:
•
Learning and Reference Guide: The Learning and Reference Guide contains all the user
information required to operate the scanner. It has detailed information as well as
step-by-step procedures. The Learning and Reference Guide is displayed on the Display
monitor.
•
Technical Reference Manual: This manual details safety information and specifications
of the system and includes power off and on procedures.
Applications Help
Although we try to make this guide complete and accurate, undocumented changes or
unexpected results do occur.
If you can't find the answer to your application question, you may call the Customer Center.
Use this phone number for non emergency purposes only, because you may not receive an
immediate response.
1. Dial 1-800-682-5327.
2. Select 1 for Applications Answer line.
3. Select 3 for CT Application assistance.
If your system fails, or you have an emergency, call
GE Cares at 1-800-437-1171.
CAUTION:
1-2
This system was designed for use by individuals trained in CT system
operation by GE Medical Systems. Study the Safety Tab of this Manual before
you scan the first patient. Use the Index to find the section and page number
of an item of interest. Periodically review the Learning and Reference Guide
and the Technical Reference Manual.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
BEFORE YOU START
CAUTION:
Improper system usage could void your warranty. More importantly, you
could endanger your patients and yourself if you don't follow the correct
procedures.
Please keep User Information readily available.
Send your comments to:
General Electric Medical Systems
CT Application (NB-911)
P. O. Box 414
Milwaukee, WI 53201-0414
U.S.A.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
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© 2005 General Electric Company. All rights reserved.
X-RAY PROTECTION
Chapter 2
X-RAY PROTECTION
CAUTION:
Improperly used X-Ray equipment may cause injury. Read and understand
the instructions in this book before you attempt to operate this equipment.
The General Electric Company, Medical Systems Group, will gladly assist and
cooperate in placing this equipment into use.
Although this equipment incorporates a high degree of protection against X-Ray outside the
useful beam, no practical design can provide complete protection. Nor can any practical
design compel a user to take adequate precautions to prevent the possibility of any person
carelessly, unwisely, or unknowingly exposing themselves or others to radiation.
Everyone having anything to do with X-Ray must receive proper training and become fully
acquainted with the recommendations of the National Council on Radiation Protection and
Measurements, and the International Commission on Radiation Protection.
NCRP reports are available from:
NCRP Publications
7910 Woodmont Avenue
Room 1016
Bethesda, Maryland 20814
CAUTION:
Everyone having anything to do with X-Ray must take adequate steps to
insure protection against injury.
All persons authorized to use the equipment must understand the dangers posed by
excessive X-Ray exposure. We sell the equipment with the understanding that the General
Electric Company, Medical Systems Group, its agents, and representatives have no
responsibility for injury or damage which may result from exposure to X-Ray.
GE urges you to use protective materials and devices.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
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2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
CT SAFETY
Chapter 3
CT SAFETY
This Technical Reference Manual explains how to operate the scanner safely. This chapter
summarizes the most important safety issues.
This manual addresses three safety classifications:
DANGER:
The most severe label describes conditions or actions which result in a specific
hazard. You will cause severe or fatal personal injury, or substantial property
damage, if you ignore these instructions.
WARNING: This label identifies conditions or actions for which result in a specific hazard.
You may cause severe personal injury, or substantial property damage, if you
ignore these instructions.
CAUTION:
This label applies to conditions or actions that have potential hazard. You may
cause minor injury or property damage if you ignore these instructions.
This manual uses pictures, or icons, to reinforce the printed message. It uses the
corresponding international symbol or icon next to the danger, warning or caution message.
For example, the upright hand with the lightning bolt across it warns of electrical hazards.
CAUTION:
Observe safe exposure factors and operating procedures to protect your
patient and yourself from physical harm during contact with this x-ray
scanner.
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© 2005 General Electric Company. All rights reserved.
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LightSpeed ™ 4.X
General Safety
Observe the basic rules of safety when you use this equipment.
•
Replace all covers before you use the equipment. The covers protect you and your
patient from moving parts or electrical shock. The covers also protect the equipment.
•
Keep the equipment clean. Remove body fluids to prevent a health risk and damage to
internal parts.
•
The table and gantry surfaces may be cleaned with a mild cleaning solution and water.
General purpose liquid disinfectant may also be used as necessary.
•
Become familiar with the functional hardware, so you can recognize serious problems.
Do not use the scanner if it appears damaged or fails.
– Wait for qualified personnel to correct the problem.
Operator Console Ergonomics
To optimally use your LightSpeed 3.X and reduce the chance of physical strain and fatigue,
the following steps are recommended regarding how you use your operator console.
Posture
Correct posture is very important. To ensure correct posture while sitting at your operator
console, follow these basic steps:
1. Face the monitors and keyboard without twisting your body.
2. Sit comfortably erect with the small of your back well supported.
3. Position your forearms parallel to the floor, with your wrists straight.
4. Position the screen so that your eyes are nearly level with the top of the screen.
5. Keep both feet flat on the footrest, with your thighs parallel to the floor.
If you cannot comfortably maintain this position while working at your operator console,
you should make the necessary adjustments to your operator console environment.
Equipment Adjustments
Chair
Adjusting the fit and height of your chair is very important for comfort. Follow these basic
guidelines:
1. Fit the backrest snugly against your back. People with shorter legs might need a back
cushion.
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© 2005 General Electric Company. All rights reserved.
CT SAFETY
2. Set your chair height to position your forearms parallel with the floor when your hands
are placed on the keyboard. If your feet dangle, you need a footrest.
Keyboard
Keyboard height is also important. When typing:
•
Your wrists should be as straight as possible.
•
Your forearms should be parallel to the floor.
•
Your hands and fingers should float over the keys or mouse.
Screen
•
The recommended viewing distance from the screen is 18 – 28 inches
(45 - 70 centimeters).
•
With your head straight, your eyes should be looking directly at the top of the screen.
•
You should look at the screen straight-on, not at an angle from the side, top or bottom.
•
Glare from the screen can disrupt your viewing and cause eyestrain. Do not face a
window, and position the screen at right angles to bright light sources.
Comfort
Comfort at your operator console indicates you've set up your work area correctly.
However even a well-designed area needs frequent adjustment, especially for different
users. Take the time when positioning yourself at your operator console to ensure your
comfort.
It is also recommended that if you use the operator console for extended periods of use
(several hours at a time), that you take short breaks to get away from your operator console
and perform simple stretching exercises to reduce the chance of fatigue.
Keep the patient in view at all times.
•
Never leave the patient unattended.
•
Stay alert to your patient's condition.
•
Use the speakers and microphones on the table, gantry, and console to stay in constant
communication, even while you sit at the console.
•
Follow the exam procedures explained in the Chapters 13 and 14 of the Learning and
Reference Manual. Carefully enter patient information and position before proceeding.
CAUTION:
Incorrect data entries or procedures could result in misinterpretation or
misdiagnosis.
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Electrical Safety
•
Avoid all contact with any electrical conductor.
•
To guarantee safe, reliable equipment performance, prepare the site according to GE
Medical Systems requirements.
•
Only allow people who know the proper procedures, and use the proper tools, to install,
adjust, repair, or modify the equipment.
•
Use GE X-Ray tubes to limit the possibility of tube melts or poor images.
CAUTION:
ELECTRICAL SHOCK HAZARD. NO USER SERVICEABLE PARTS. REFER SERVICE
TO QUALIFIED SERVICE PERSONNEL.
Regulatory Requirements
NOTE: This equipment generates, uses, and can radiate radio frequency energy. The
equipment may cause radio frequency interference to other medical and
non-medical devices and radio communications. To provide reasonable protection
against such interference, this product complies with emission limits for Group 1 Class
A Medical Devices as stated in EN 60601-1-2.
However, there is no guarantee that interference will not occur in a particular installation. If
this equipment is found to cause interference (which may be determined by switching the
equipment on and off), the user (or qualified service personnel) should attempt to correct
the problem using one or more of the following measures:
•
Re-orient or relocate the affected device(s)
•
Increase the separating space between the equipment and the affected device
•
Power the equipment from a source different from that of the affected device
•
Consult the point of purchase or the service representative for further suggestions
The manufacturer is not responsible for any interference caused either by the use of
interconnect cables other than those recommended or by unauthorized changes or
modifications to this equipment. Unauthorized changes or modifications could void the
user`s authority to operate the equipment.
To comply with the regulations applicable to an electromagnetic interface for a Group 1
Class A Medical Device, all interconnect cables to peripheral devices must be shielded and
properly grounded. Use of cables not properly shielded and grounded may result in the
equipment causing radio frequency interference in violation of the European Union Medical
Device directive and FCC regulations.
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© 2005 General Electric Company. All rights reserved.
CT SAFETY
This product complies with the regulatory requirements of the following:
•
Council Directive 93/42/EEC concerning medical devices when it bears the following CE
marking of conformity
0459
For a system, the location of the CE marking label is described in the system manual.
European registered place of business:
GE Medical Systems Europe
Quality Assurance Manager
BP 34
F 78533 BUC CEDEX
France
Tel +33 1 30 70 40 40
•
Green QSD 1990 Standard issued by MDD (Medical Devices Directorate, Department of
Health, UK).
•
Medical Device Good Manufacturing Practice Manual issued by the FDA (Food and Drug
Administration. Department of Health, USA)
•
Underwriters' Laboratories, Inc. (UL), an independent testing laboratory.
•
Canadian Standards Association (CSA)
•
International Electrotechnical Commission (IEC) International standards organization,
when applicable.
General Electric Medical Systems is ISO 9001 certified.
This symbol indicates that waste electrical and electronic equipment must not
be disposed of as unsorted municipal waste and must be collected separately.
Please contact an authorized representative of the manufacturer for
information concerning the decommissioning of your equipment.
Electromagnetic Compatibility (EMC)
1. Under certain atmospheric conditions, Electro-Static Discharges (ESD) of 8kV in the
vicinity of the Gantry Display and/or Patient Microphone Assembly may result in
degradation of system operation:
a) Non-Scanning Mode: Gantry Display may momentarily flicker. System operation
returns to normal when the ESD disturbance subsides
b) Scanning Mode: Gantry Display may momentarily flicker. The ESD disturbance could
possibly abort a scan in progress, requiring the Operator to select RESUME to
continue scanning when the ESD disturbance subsides.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
3-5
LightSpeed ™ 4.X
2. Under certain atmospheric conditions, Electro-Static Discharges (ESD) of 6kV in the
vicinity of the Operators Console front cover may result in degradation of system
operation:
a) All modes: Control of the electronic mouse may be disrupted, requiring the Operator
to restart the system when the ESD disturbance subsides.
3. Under certain atmospheric conditions, Electro-Static Discharges (ESD) of 6kV in the
vicinity of the Gantry Display, Patient Microphone Assembly, Gantry Mylar Window
Bands, and various exposed metal components of the Table and Console may result in
degradation of system operation.
4. All modes: Audible interference may be detected through the system intercom.
Operation returns to normal when the ESD disturbance subsides.
5. Under certain site configurations, Electrical Fast Transient (EFT) burst(s) (+/- 1 kV or
greater) which are capacitively coupled to the Operator's Console interconnect cables
may result in degradation of system operation:
6. All modes: Control of the electronic mouse may be disrupted (can't move mouse).
Operation returns to normal when the EFT disturbance subsides.
7. Under certain site configurations, Electrical Fast Transient (EFT) burst(s) (+/- 500V or
greater) which are capacitively coupled to certain system interconnect cables may
result in degradation of system operation:
8. All modes: Audible interference may be detected through the system intercom.
Operation returns to normal when the EFT disturbance subsides.
9. Under certain conditions operating a cell phone in the near proximity of the gantry in
the scan room during scanning modes, patient data may be lost.
10. Under certain conditions, when the system is exposed to Radio Frequency (RF) levels of
3 volts/meter at the following frequencies: 27.11MHz, 40.56MHz, 433.92MHz, system
operation may be degraded:
11. All modes: Audible interference may be detected through the system intercom.
Operation returns to normal when the RF exposure subsides.
a) Low signal: When the system is exposed to an external RF field, image streak
artifacts may be detected while scanning under conditions of low X-Ray signal, such
as when scanning large patients. Operation returns to normal when the external RF
field is removed.
EMI/EMC Glossary Terms:
ElectroMagnetic Compatibility (EMC): The ability of an electronic system not to be a source
of pollution by electronic emission to the environment in which it operates. Both radiated
and conducted emissions contribute directly to the interference-causing potential of an
electronic system.
3-6
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
CT SAFETY
ElectroMagnetic Interference (EMI): The ability of an electronic system to function properly
in its intended environment, without susceptibility to interference from external sources.
Susceptibility is the capability of an electronic system to:
•
Respond to unwanted electrical energy
•
Operate satisfactorily, without degradation, and with a defined margin of safety
Emergency Stop
NOTE: Every operator should take a few minutes to locate the Emergency Stops on his or
her system before he or she scans the first patient.
The system has one Emergency Stop on the Console and one Emergency Stop with each set
of Table/Gantry controls.
All Systems
Press the EMERGENCY STOP button:
•
When the system loses control of the table or azimuth drives.
•
To stop all scanner motion, table motion and X-Ray.
•
To remove the power to the X-Ray tube filament.
•
When Emergency Stop is applied, the moving cradle and tilting gantry may overrun by
less than 10 mm and less than 0.5 degrees respectively.
NOTE: Press EMERGENCY STOP if the cradle, table, or gantry starts to move unexpectedly.
NOTE: Press System Emergency OFF (SEO) on the wall in the event of fire, flood, earthquake,
or if you see smoke.
Emergency Stop Locations
SEO
Intercom
Speaker
Emergency Stop removes power to
the table drives, gantry drives, and X-Ray system
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
3-7
LightSpeed ™ 4.X
Emergency Power Shutdown
Your system provides two levels of emergency power shutdown:
•
Emergency Stop: Disables all drives and X-Ray power
•
System Emergency OFF: Removes power from entire system.
Emergency Stop: Each system has five EMERGENCY STOP buttons: one on the operator
console, and one with each set of gantry controls.
NOTE: If the cradle or table starts to move unexpectedly, press any EMERGENCY STOP to
remove power to the gantry, table, and X-Ray system. Slide the cradle by hand to
move it out of the gantry.
System Emergency OFF (SEO): Each facility should have a wall mounted SEO near the
Operator Console (OC).
•
Press the red, circular SEO to instantly remove all power to the entire system,
including OC.
•
The SEO removes power to the Mains Disconnect Control (MDC), also known as A1.
NOTE: To instantly remove all power, press the System Emergency OFF SEO switch on
the wall.
Emergency Patient Care During X-Ray ON:
•
Press STOP SCAN to abort x-ray and stop gantry/table movement.
•
Press PAUSE SCAN to pause scanning after the current scan completes.
•
During an exam, the system pauses between scans if you Press any button on the
control panel other than the alignment lights. It stops X-Ray if you Press the same
button(s) during a scan.
•
Select Resume on the screen to continue the exam.
Restore System After Emergency Stop
Systems With Gantry Control Panels
•
Press EMERGENCY STOP
Table drives.
to remove power to the gantry drives, X-Ray system and
– The Gantry RESET LED flashes about once every 2 seconds whenever you press any
of the system emergency stops.
•
Press the flashing RESET LED
on the gantry control panel to restore power to the
drives, X-Ray system and table drives.
– Emergency Stop: The RESET LED flashes about once every 2 seconds when you
press an EMERGENCY STOP.
3-8
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
CT SAFETY
Restore System Emergency OFF
•
When you press a System Emergency OFF SEO switch, you remove power to the Mains
Disconnect Control (MDC), also known as A1.
– Press the MDC START button to restore its power.
NOTE: Press the System Emergency OFF SEO switch to instantly remove power to the entire
system.
Systems With Gantry Control Panels Only
•
Press the START button on the Mains Disconnect Control (A1) to restore power to the
PDU, Console(s) and subsystem electronics.
•
Press the RESET
button on the Gantry Control panel to restore power to the Gantry
drives, X-ray system, and Table drive.
Radiation Safety
NOTE: We cannot guarantee performance or safety if you use a non GE X-Ray tube, because
cooling and reconstruction algorithms depend upon the tube design. Radiation
leakage may exceed GE specifications when a non GE X-Ray tube is installed in the
scanner.
•
Press and release move to scan from the console to advance the cradle during Auto
Scan.
•
If you select Auto Scan during one group Rx, it remains ON for every group in that series.
•
Stay behind a lead screen or lead glass shield during each X-Ray exposure.
•
Use technique factors prescribed by the radiologist or diagnostician. Use a dose that
produces the best diagnostic results with the least X-Ray exposure.
•
Never calibrate, test the scanner, or warm the tube with patients or personnel present in
the scan room.
•
Amber indicator lights on the gantry display panel, and rear of the gantry, illuminate
during X-Ray exposure.
The scanner uses cooling and reconstruction algorithms specifically designed for GE
X-Ray tubes.
You risk two dangers when you do not use GE X-Ray tubes.
•
A non GE tube could overheat and explode if the cooling delays do not meet its design
requirements.
•
The images could exhibit artifacts if your X-Ray tube fails to conform with GE tube
performance specifications
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
3-9
LightSpeed ™ 4.X
NOTE: If you fail to follow safe X-Ray practices, or ignore the advice presented in this book,
you and your patient risk exposure to hazardous radiation.
SmartStep Safety
The SmartStep option adds several components to the scan room. These are the In-Room
Monitor, Hand Held Control for table movement as well as image review, and the X-Ray
Control Footswitch.
Each of the SmartStep components is connected to the system by a cable. When using the
system, ensure that the cables cannot catch on anything when the gantry or table is
moved.
Table Float
During SmartStep the Clinician has the option to float the table between scans. When the
Table Float mode is selected, the table is unlatched and can be moved freely by anyone at
the bedside.
CAUTION:
UNINTENDED TABLE MOTION COULD CAUSE A SERIOUS INJURY. TABLE MAY BE
BUMPED OR JARRED DURING AN INTERVENTIONAL PROCEDURE. CARE MUST
BE TAKEN WHEN PERFORMING INTERVENTIONAL PROCEDURES IN THE FLOAT
MODE. IT IS THE CLINICIAN'S RESPONSIBILITY TO ENSURE THAT THEY HAVE
CONTROL OF THE TABLE WHEN IN THIS MODE OF OPERATION. TABLE MUST
NOT BE LEFT UNATTENDED WHEN IN THE FLOAT MODE. ENSURE THAT THE
TABLE IS LATCHED BEFORE LEAVING THE TABLE SIDE.
SmartStep Scanning
SmartStep scanning allows multiple scans at one location for interventional procedures.
The system allows up to 90 seconds of scanning in one place. After 90 seconds, the
operator must prescribe a new scan to continue. The accumulated scan time from a
procedure is displayed in the In-Room Monitor.
CAUTION:
Prolonged exposure to x-ray in one spot may cause reddening or radiation
burns. User must be aware of the techniques used and exposure time to insure
safe operation.
Clinician's working in the scan room should wear appropriate protective clothing. Lead
aprons, groin and thyroid protection, as well as protective eyewear are available through
the GE accessories Catalog.
3-10
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
CT SAFETY
Mechanical Safety
CAUTION:
TO PREVENT PINCHING OR CRUSHING OF THE PATIENT'S EXTREMITIES, KEEP
THE PATIENT'S HANDS AND FEET AWAY FROM THE EDGE OF THE MOVING TABLE
TOP/CRADLE AND ITS SURROUNDING EQUIPMENT, OR BETWEEN TABLE BASE
AND SIDE PANELS OF TABLE. (TAKE SPECIAL CARE WHEN POSITIONING
OVERWEIGHT PATIENTS.
CAUTION:
TO PREVENT PINCHING OR CRUSHING THE PATIENT, WATCH THE PATIENT AND
EQUIPMENT CAREFULLY AT ALL TIMES DURING GANTRY TILT, OR TABLE
MOVEMENT. IF UNWANTED MOVEMENT OCCURS, OR MOTION DOES NOT STOP,
PRESS ONE OF THE EMERGENCY STOP SWITCHES ON THE KEYBOARD, OR
GANTRY.
•
Physically assist all patients on and off the table, and into position on the cradle. Return
the gantry to the 0 degree upright position, latch the cradle and adjust the table to a
comfortable height for patient loading and unloading.
•
A green indicator lights on the gantry display panel when the cradle unlatches. Latch
the cradle before you load the patient. An unlatched cradle slides away from you.
– Press
•
on the control panel to latch the cradle drive.
Avoid any patient contact with the gantry during tilt or cradle movement (manual or
software driven).
– Once again, pay close attention to large patients; make sure you don't pinch skin or
extremities between the cradle and the gantry.
– Table Tape Switch: If someone or something touches the switches, the table motion
will stop and the table latch icon will flash once per second. To reset the stop, simply
move the table away from the obstruction.
•
A green icon indicates the cradle reached a travel limit or encountered an interference.
– IF the table reaches a limit while you are using the controls, the interference light
turns OFF when you release the button.
– IF the light results from resistance, the light continues to flash until the you clear the
condition.
•
Be especially careful when tilting the gantry or moving the table when the cradle
extender or head holder is in place to avoid driving these accessories into the gantry
covers.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
3-11
LightSpeed ™ 4.X
Clear an interference by changing the gantry tilt, moving the cradle, or adjusting the
table height.
•
Check the lengths of all patient health lines (IV tubing, oxygen line, etc.) and make sure
they accommodate cradle travel.
– Position these lines so they cannot catch on anything within the patient vicinity or
between the table and gantry during cradle travel or gantry tilt.
•
Do not use the table base as a foot rest. You could entrap and injure your foot while
lowering the table. Do not place your hands between the table base and the table side
panels.
•
Don't place your hands inside the gantry cover when tilting the gantry. The gantry can
pinch or crush your hands!
Periodically check all accessories for damage and remove them from service if damaged
or cracked.
•
Check the accessory attachment plate fixed to the end of the cradle. Repair or replace if
loose or damaged.
•
Use the cradle extender to support the patient's head or feet during a scan study.
CAUTION:
Head holder may crack, possibly injuring the patient's head or neck, if the
patient tries to brace themselves on the head holder during positioning.
CAUTION:
Head holder is only designed to support 75 lb (34 kg). Ask patient to scoot up
into head holder or manually aid them into position.
•
The metal free cradle extender supports up to 34 kg (75 lb); both of the metal free head
holders support up to 34 kg (75 pounds).
•
None of the accessories support the full weight of a patient. If you sit, stand or
otherwise apply excessive pressure to these devices, they will break or come off the
cradle, and may cause injury.
CAUTION:
•
The patient positioning straps provided with the system do not support the
full weight of the patient. Patient positioning straps should be used to aid in
patient positioning and are not meant to fully restrain the patient.
The concentrated weight of short, heavy patients can cause the cradle to make contact
with the gantry.
– Make sure you don't drive the cradle into the gantry cover.
– Make sure you don't pinch skin or extremities between the cradle and the gantry.
3-12
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
CT SAFETY
IV Pole Safety
Care should be taken in the amount of weight and ensuring that the pole is tightened prior
to use.
CAUTION:
The IV pole may bend when excessive weight is placed on the pole. Ensure no
more than 4.5 kg or 10 lb is placed on the IV pole.
CAUTION:
The height of the pole may move on it's own without proper tightening of the
IV pole extension collar. Ensure that the extension collar is tightened prior to
use.
Table Tray Safety
Care Should be taken with the weight and Objects placed on the tray.
CAUTION:
The maximum allowable weight on the table tray is 9kg or 19.8 lbs
CAUTION:
Objects that may be susceptible to tipping should be strapped down with the
Velcro strap provided.
Systems With Metal-Free Cradles and Accessories
CAUTION:
•
Prevent damage to metal-free accessories! Carefully examine the metal-free
clasp assembly on the accessory and the catch on the cradle before
attempting to attach the accessory for the first time.
To Latch an accessory:
– Align the accessory tongue with the pocket at the end of the cradle.
– Keep fingers clear of the cradle.
– Push the tongue all the way into the pocket until it latches into place.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
3-13
LightSpeed ™ 4.X
•
To Unlatch an accessory:
– Pinch the two L-shaped parts together and pull the accessory out of the cradle.
– An alternate method is to apply a light force to the catch in the direction to pull the
accessory out of the cradle.
•
Proper operation:
– Keep the accessory “tongue” and cradle pocket clean and free of fluids and debris.
– Keep the latch and cradle pocket area clear of sheets, drapes, pads or any item that
could interfere with proper latching and cause damage.
If the Cradle Fails to Advance:
•
Check table height. The cradle won't advance until the table height permits it to clear
the gantry opening.
•
Check the cradle latch. The unlatched icon lights on the gantry display panel when the
cradle unlatches.
•
If you recently restored table power, move the cradle to make sure it latches.
Table Locked
•
Table Load Capacity:
– up to 180 kg (400 lb) with +/-0.25 mm positional accuracy guaranteed
– 180–205 kg (400–450 lb) maximum allowed with normal operation and +/-1mm
positional accuracy
CAUTION:
•
GE cannot guarantee precise location accuracy at weights from 180–205 kg
(400–450 lb).
Move the cradle all the way out of the gantry for safe and easy patient loading.
– The cradle locks when positioned all the way outside the gantry opening. It clicks
when it locks.
– The green gantry display panel light on indicates a un-latched cradle.
CAUTION:
3-14
DO NOT PLACE A PATIENT ON THE TABLE WEIGHING MORE THAN THE UPPER
LIMIT OF 205 KG (450 LB). THIS COULD CAUSE THE TABLE TO FAIL AND THE
PATIENT COULD FALL.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
CT SAFETY
Laser Safety: Warning Labels
CAUTION:
•
THE LASER BEAM CAN CAUSE EYE INJURY.
The following warning labels are located at the bottom of the Gantry cover:
CAUTION
LASER RADIATION
DO NOT STARE INTO BEAM
635, 670 nm LASER DIODE
1.0 MILLIWATT MAXIMUM OUTPUT
CLASS II LASER PRODUCT
LASER RADIATION
DO NOT STARE INTO BEAM
CLASS 2 LASER PRODUCT
•
Labels on the front of the gantry warn:
LASER APERTURE
Do not stare into beam
•
When using a 635nm laser assembly inside the gantry has the following label to warn
service personnel not to look directly at the beam:
AVOID EXPOSURE
LASER LIGHT EMITTED
FROM THIS APERTURE
CAUTION
LASER LIGHT – DO NOT
STARE INTO BEAM
PEAK POWER 1MW
WAVELENGTH 635NM
CLASS II
LASER PRODUCT
Tell head study patients to close their eyes before you switch ON the alignment lights.
NOTE: Closely monitor infants and infirm patients, and prevent them from accidently staring
into the beam.
•
The
indicator on the gantry display panel lights when you turn ON the alignment
lights.
•
Instruct your patients to keep their eyes closed until you turn OFF the alignment lights.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
3-15
LightSpeed ™ 4.X
CAUTION:
Use of controls or adjustments, or performance of procedures other than
those specified herein, may result in hazardous radiation exposure.
CAUTION:
THE DETECTOR AND DAS ROTATE TO POSITION THE ALIGNMENT LIGHTS OVER
THE LASER PORTS.
•
Keep your hands away from the gantry opening.
•
Make sure the gantry side covers are in place.
•
The gantry rotating base assembly could seriously injure or kill.
Operator Console
Location of Emergency Stop
Press EMERGENCY STOP to remove power to the table drives, gantry drives, and X-Ray
system.
3-16
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
CT SAFETY
Image
Monitor
Scan Monitor
Bright Box
O
Mouse Pad
Keyboard
Mouse
Safety
Section
Intercom
Section
Interface
Cable
Table/Scan
Control
Section
14
15
11
7
10
8
12
13
9
4
1
5
2
6
3
No. Function
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Start Scan Button
Pause Scan Button
Stop Scan Button
Move to Scan Button
Stop Move Button
Prescribed Tilt Button
Patient Speaker Volume Control
Autovoice Volume Control
Operator Speaker Volume Control
Speaker
Microphone
Talk Button
Autovoice ON Indicator
E-Stop Button
X-Ray ON Indicator
Keyboard Tray
CAUTION:
Connections for the keyboard and mouse are accessible on the front of the
GOC1 operator console. DO NOT DISCONNECT OR CONNECT THESE DEVICES
UNLESS THE POWER TO THE CONSOLE IS OFF.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
3-17
LightSpeed ™ 4.X
Gantry and Table
Location of Emergency Stop
Systems with Gantry Control Panels
SEO
Emergency Stop Locations
Intercom
Speaker
Emergency Stop removes power to
the table drives, gantry drives, and X-Ray system
Prepare the Cradle/Patient
Prepare the Cradle
•
Position the gantry to zero degrees tilt.
•
Install accessories such as a headholder, cushions, security straps, cradle extender.
•
Check for contrast agent from the previous study.
•
Lock the table into the load position:
– Drive the cradle all the way out of the gantry.
– Lower the table to minimum height.
CAUTION:
Always return the gantry to zero degrees before lowering the table. Failure
to do so may result in the headholder, coronal headholder, or foot extender
striking the gantry and breaking.
Prepare the Patient
3-18
•
Review the protocol chart for positioning, technique, contrast, and reconstruction
suggestions.
•
Always help the patient onto the table.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
CT SAFETY
•
Position the patient feet first when the exam requires an injector or IV, to prevent
interference with the gantry during cradle motion.
•
Monitor all equipment motions to prevent collisions.
•
Check for obstructions before moving the system.
NOTE: Make sure the actual patient entry and orientation matches the prescription entries.
CAUTION:
Keep the patient in view at all times. Insure that the patient can be seen while
you are at the operator console. Never leave the patient unattended while
they are on the table.
Helical Safety
WARNING: Helical scanning has the inherent ability to produce artifacts when scanning
highly sloped anatomy (e.g. pediatric or adult heads). Factors which worsen
this effect are: faster table speeds, wider image thickness, and gantry tilt. In
some cases these artifacts could be mistaken for a hemorrhage near the
cranium, or a thickening of the skull.
WARNING: To reduce the occurrence of these artifacts you may prescribe slower table
speeds and/or thinner slices (such as 2.5mm) during helical scans near the
vertex of a pediatric or adult head
WARNING: It has been documented in radiology literature than an artifact may occur in
the chest that bears the double margin of the great vessels, which emulates
a dissection of the vessel during 0.5 – 1.0 second scans. This can occur in axial
or helical scans. If you have scanned axially or helically with a 0.5 – 1.0 second
rotation time and observe this phenomenon, rescan the area with a 2 second
axial scan to verify if it is artifact or patient pathology.
WARNING: For helical scans, the Segment Recon Mode in Retrospective Recon may be
used to assess if there is an artifact or not. If questions still arise, then rescan
the area with a 2 second Axial scan.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
3-19
LightSpeed ™ 4.X
Cardiac Imaging Safety
CAUTION:
A patient with the following conditions may be difficult to examine:
A) Patients having multiple PVC’S
B) Patients with extreme arrhythmia
C) Patients with dual-chamber pacemakers
If examined, the software may not be able to detect the R-peaks and the
images therefore may be produced as un-gated segment images.
3-20
CAUTION:
If an EKG lead falls off during the scan, or the heart rate drops below 40 BPM,
the images will be reconstructed as non-gated segment images. This is done
to avoid inaccuracy of the z-location of images where necessary.
CAUTION:
SnapShot Segment is designed for patients with a heart rate of 75 BPM or
lower. It is not recommended to scan a patient with a heart rate above 75
BPM. If a patient has been scanned with a heart rate higher than 75 BPM, the
temporal resolution will be inadequate in freezing the motion of the heart,
decreasing image quality.
CAUTION:
A cardiac exam may have insufficient image quality due to patient motion,
breathing artifacts, or an increase in the heart rate of 10 – 20 BPM (e.g., 60 –
80 BPM). It is important to explain to the patient about the hot feeling when
the contrast is injected, and stress the importance of proper breathing.
CAUTION:
If, during the scan, the heart rate drops significantly lower than the
prescribed heart rate, there is a potential for image location gaps. To avoid
image location gaps, a non-gated image is reconstructed for the period where
the heart rate dropped below the prescribed heart rate. A non-gated image
may have more motion and may not be reconstructed at the prescribed
phase.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
CT SAFETY
CAUTION:
There is a possibility that the EKG signal may not be detected by the scanner
due to improper lead placements, or a lead falling off during the scan. It is
important to place new leads on the patient before the scan. Make sure the
leads are attached properly, and use the recommended EKG leads specified
in this chapter.
Accuracy of Measurements
Measure Distance for Axial, Helical, and Cine Images
Measure error using the straight line distance graphic is less than 2 times the image pixel
size.
Measure Distance for Scout Images
Accuracy of measurements for scout images in the “X” direction varies with object thickness
and distance from ISO in the “Y” direction. Note the orientations of the “X” and “Y” in the
diagram below assume a scout scan plane of 0 degrees. If the scout plane is rotated then
the “X” and “Y” orientation changes respectively.
•
For measurements of anatomy in the “X” direction that are at ISO center (“Y”):
– The measure error using the straight line distance graphic is less 5% of the
measured distance plus 2mm.
•
For measurements of anatomy in the “X” direction that are NOT at ISO (“Y”):
– The measure error using the straight line distance graphic is less 5% of the
measured distance plus 2mm plus 3% of measured distance per centimeter
from ISO.
•
For measurements of anatomy in the “Z” direction:
– Measure error using the straight line distance graphic is less than 2 times the image
pixel size.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
3-21
LightSpeed ™ 4.X
Scout Scan Plane = 0 Degrees
"ISO
Center"
"Y"
"X"
"Z"
Patient Table
Measure Angle
Measurement accuracy using the angle graphic is equal to the displayed angle value +/- 10
degrees for an angle measured between segments which are five times larger than the
image pixel size.
Accuracy improves as the length of the segments increases.
ROI
Area measurement accuracy using a region of interest graphic (rectangle, smooth curve,
ellipse or free draw) is equal to the displayed area +/- the circumference of the region
multiplied by (image pixel size)2/2. Mean and standard deviation values for the intensity of
the pixels in the region are also affected by this accuracy.
If the ROI is rotated, the area measurement can vary up to 5%.
Region of interest statistics are based on the pixels INSIDE the graphic defining the region.
Reformat Plane Thickness
Reformat plane thickness equals 1 pixel.
3-22
•
If each axial pixel represents 0.5mm or anatomy, then the reformat plane thickness
equals 0.5mm.
•
If pixel size equals 0.9766mm (500mm/512), then the reformat plane represents a slice
of anatomy about one millimeter thick.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
CT SAFETY
Lung Algorithm
•
The Lung algorithm setting provides edge enhancement between structures with large
density differences, such as calcium and air, resulting in a sharper lung field when
compared to Standard algorithm.
•
For best image quality, prescribe a 10mm, 7.5mm or 5mm scan thickness when you
plan to use the Lung algorithm. If you plan to prescribe a High Resolution Lung study
with 3.75, 2.5, or 1.25mm, use the Bone algorithm.
•
The Lung setting enhances the contrast of small objects. For best viewing and film
quality, select a window width of 1000 to 1500 and a window level of -500 to -600.
•
The Lung algorithm setting increases the CT number values at the edge of high contrast
objects. If you plan to take CT number measurements of vessels or nodules in the lung,
please check and compare your results with Standard algorithm images. (ROI and
Histogram functions use CT numbers.)
•
Remember: The edge enhancement provided by the Lung setting may not be
appropriate in some clinical cases. Please take individual viewing preferences into
account when you choose the Lung setting.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
3-23
LightSpeed ™ 4.X
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3-24
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
ACCESSING THE LEARNING AND REFERENCE GUIDE
Chapter 4
ACCESSING THE LEARNING AND
REFERENCE GUIDE
The Learning and Reference Guide is designed to get you up and running your system. It is
recommended that each system operator review the complete Learning and Reference
Guide.
To start the Learning and Reference Guide:
•
Select the [Learning Solutions] icon.
•
Select the language you wish to review in.
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TUBE WARMUP
Chapter 5
TUBE WARMUP
To maintain image quality and long tube life, complete the Warmup procedure.
•
Display the Scan Monitor screen.
•
Select Daily Prep and Tube Warmup to display the Warmup screen.
– When you haven't used the X-Ray tube for more than three hours
– Fastcal - Tube warmup runs automatically when Fastcal is selected.
– Before Calcheck
– Before system calibration
GE suggests you warm up the tube after every three hours of non-use.
The system displays the following message on the Scan Monitor screen:
Scans may have been taken within the last three hours. Warmup scans may cause
subsequent tube cooling delays.
If you press CANCEL , the tube warmup will be cancelled.
NOTE: Tube warmup will run in Autoscan mode.
•
Read the compatibility Warning.
•
Position the gantry to 0° tilt.
•
Click [Accept] when you understand the implications.
•
Tube warmup runs a set of tube heating scans.
•
When finished, the system display returns to the daily prep screen.
A message that tube warm-up has been completed will also be in the system message log.
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DAILY FAST CAL PROCEDURE
Chapter 6
DAILY FAST CAL PROCEDURE
To maintain image quality, complete the Fast Cal procedure once a day.
1. Display the Scan Monitor screen.
– Clear the gantry opening.
– Raise the table above the patient loading level.
2. Select [Daily Prep] and [Fast Cal] to display the screen.
– Before the start of every scan day
– Before Cal check
– Before system calibration
3. The system automatically selects the Auto Scan function.
a) The system automatically selects the following sequence of scans:
– Mylar Window Check
– Cold Warmup
– Warmup 1
– Warmup 2
– Collimator Cal
– FPA Check Scans
– Clever Gain Calibration
– Fast Calibration
b) Follow system instructions to initiate the first scan, and the system acquires the rest
of the scan set.
c) Remain near the console during auto scan acquisition, so you can stop X-Ray if
someone enters the scanner room.
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© 2005 General Electric Company. All rights reserved.
PREPARE THE SYSTEM
Chapter 7
PREPARE THE SYSTEM
•
Clean the Accessories and check for damage.
•
Check and remove dried contrast agent from:
– Mylar ring (around the gantry opening)
– Detector window
– Table extension and cradle surfaces — especially the Patient Restraint plastic
channels on the table
– Accessories (Head holders, pads and cushions, etc.)
•
Check supplies.
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© 2005 General Electric Company. All rights reserved.
CHECK DISK SPACE
Chapter 8
CHECK DISK SPACE
Maintain Image and Scan file space on the disk, because the system refuses to scan when it
runs out of file space.
Check Image Space
•
Check the daily schedule, and multiply the list of patients by the estimated number of
images each study requires.
•
Compare your estimate to the remaining 5122 images listed in the Feature Status Date
and Time area.
•
If your estimate exceeds the available Image Space:
– Film any previously unfilmed studies. (Optional)
– Transfer designated images to another suite or console.
– Archive and remove the oldest images from the system disk.
Always follow the filming and archive routines established for your facility.
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© 2005 General Electric Company. All rights reserved.
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© 2005 General Electric Company. All rights reserved.
RESET THE SYSTEM
Chapter 9
RESET THE SYSTEM
System Shutdown/Reset Procedures
To prevent system software problems, restart your system once every 24 hours.
(Recommended: Shutdown and restart at the end of the last shift.) If the system has a
persistent problem, record the time, circumstances, and error messages, then call service.
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© 2005 General Electric Company. All rights reserved.
STOP/START THE OPERATING SYSTEM
Chapter 10
STOP/START THE OPERATING
SYSTEM
Octane Based Systems
To turn off main disconnect control (MDC) or A1.
Shutdown the system.
1. On Display Monitor, click the Shutdown icon.
•
Dialog is posted
2. Select OK.
•
Dialog will be posted
– Attention
System is shutting down please wait …
•
Another dialog will be posted.
– The system is shutting down please wait …
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10-1
LightSpeed ™ 4.X
•
When the system is down a dialog is posted
– Okay to power off system now
3. Press the STOP button on the MDC or A1 connector panel.
4. To start operating system from Okay to Power off System Prompt, select Restart on the
display monitor.
•
Dialog is posted on the display monitor
– The system is coming up please wait …
5. A dialog box will be posted
– Attention
OC is initializing please wait…
6. When this dialog disappears the system is ready to use.
PC Based System
To turn off main disconnect control (MDC) or A1.
Shutdown the system.
1. On Display Monitor, select Shutdown.
•
Dialog is posted
2. Select Shutdown and click OK.
•
Dialog will be posted
– Attention
System is powering down please wait …
•
Another dialog will be posted.
– The system is shutting down please wait …
•
When the system is down a dialog is posted
– Okay to power off system now
3. Press the STOP button on the MDC or A1 connector panel.
10-2
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
STOP/START THE OPERATING SYSTEM
4. To start operating system from Okay to Power off System Prompt, click Restart on the
display monitor.
•
Dialog is posted on the display monitor
– The system is coming up please wait …
•
A dialog box is posted
– Attention
OC is initializing please wait…
•
When this dialog disappears the system is ready to use.
5. If your system has the HIPAA login enabled, you are required to login to the system.
If You Turn OFF the MDC at the End of the Scan Day:
To start the system if main disconnect has been powered off:
•
Press the START button on the main disconnect control (A1).
Systems with Gantry Control Panels:
1. Push the START button on the main disconnect control (A1) to restore power to the PDU,
console(s) and subsystem electronics.
2. Push the RESET button
to turn on the Gantry Control panel to restore power to the
Gantry drives, X-Ray system, and Table drive.
•
When this dialog disappears the system is ready to use.
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© 2005 General Electric Company. All rights reserved.
General Information
Chapter 11
General Information
This section provides a simple introduction to CT, or Computed Tomography, for people with
no detailed physics or medical diagnostic education.
System components:
•
The system components are explained in the Learning and Reference Guide.
GE Healthcare products are designed to provide optimum performance with GE-supplied
parts. Accordingly, GE can make no assurances that Equipment performance will not be
affected by the use of non-GE-supplied parts. In some instances use of non-GE-supplied
parts may affect Equipment performance or functionality.
To enhance user awareness when non-GE-supplied tube are in use, the Equipment has been
designed to recognize GE-supplied tubes and report to the user the presence of a
non-GE-supplied tube. This will permit the user to make any adjustments to Equipment use
that the user deems appropriate. Use of the Equipment with non-GE-supplied parts is
always at the user’s discretion. GE assumes no liability for the use of non-GE-supplied parts
and disclaims any responsibility for any affect such parts may have on Equipment
performance.
Emergency Stop:
•
Emergency Stop procedures are described in the CT Safety tab.
Intended Use
This system is intended to be used for head and whole body computed tomography.
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11-1
LightSpeed ™ 4.X
CT Description
In conventional radiography, X-Rays pass through the patient to a film, which records
anatomic “shadows.” The X-Rays create a planar image, called a radiograph.
In computed tomography, electronic circuits detect and measure the X-Rays, and send
these measurements to a computer system that converts the information to a pixel value
matrix. These pixel values appear as a two dimensional image on a CRT monitor. Even
though CT creates X-Ray exposures, we normally refer to them as images.
Additional computer software permits you to manipulate, shade, rotate, correlate, and
measure the images to derive even more information. The system also provides the means
to store the images on permanent or temporary media.
Conventional radiography can discern tissue density differences of 5%. CT can distinguish
density differences of 1% or less.
Traditional CT systems collect 1 row of data at a time. The Lightspeed 4.X CT scanner
system may improve customer productivity and open the door for new applications and
unparalleled scan speeds via a revolutionary 16-row data acquisition system.
CT Operation Theory
The PDU (power distribution unit) distributes system power. Power travels from the PDU to
the gantry. The components that produce X-Rays reside inside the gantry. The generator
produces high voltage, and transmits it over the slip rings to the X-Ray tube. High voltage
propels electrons from the X-Ray tube filament to its anode. Heat and x-radiation result.
The X-Ray tube’s heat capacity and dissipation determine the frequency and length of CT
exposures. A Helical and Cine exposure can last up to 120 seconds and Axial exposures last
from 0.5 to 4 seconds.
The scintillator material in the detector absorbs the X-Ray that passes through the patient,
and generates a corresponding level of light. The detector converts the light levels into a
corresponding electric current. The DAS (Data Acquisition System) samples each detector
cell in all 16 detector rows about 1640 times per second, amplifies and quantifies the
existing current, then sends the resulting data to the IG (Image Generator).
Each complete sample by the DAS is called a view. The recon engine converts all the views
into a single matrix of pixel values, called an image. The display processor takes a copy of
the digital matrix data, and converts it into television shades of gray, and sends the image
to the CRT monitor for display. The OC (operator console) contains the CRT monitor and
controls the computer, X-Ray, and cradle drives.
DICOM Print
The LightSpeed 4.X can send a camera request to a camera that has DICOM print
capabilities.
11-2
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© 2005 General Electric Company. All rights reserved.
General Information
X-Ray
The X-Ray tube contains filaments, a cathode and an anode. The filament provides the
electrons that create X-Rays. The X-Ray system generates a current that heats the filament
until electrons start to “boil off” and break away from the filament. We refer to the filament
current as “mA.” Increasing the mA increases the number of electrons that become available
to make X-Ray. Higher concentrations of electrons improve image resolution.
The X-Ray system creates a high voltage, or kV, potential between the cathode and anode.
The negative charge on the cathode repels the electrons that boil off the filament. The
positive charge on the anode attracts the negatively charged electrons. The electrons strike
the rotating anode target and displace electrons in the target material. This interaction
creates heat and X-Ray photons. The target rotates to help spread the heat over a larger
area. Increasing the kV increases the electron strike speed, which in turn increases the
intensity or “hardness” of the X-Ray photon beam.
X-ray must reach the detector reference
cells at the edges of the selected SFOV.
X-Ray Tube
Centered Patient
Gantry Opening
Detector
DAS
Tube Warmup
Warmup provides an automated group of low technique exposures designed to safely bring
the X-Ray tube to operating temperature before you start to scan for the day. Warmups
increase tube life and help produce more consistent, quality images.
LightSpeed 4.X Theory of Operation
System Overview
The LightSpeed 4.X CT scanner is a premium-tier, 3rd generation CT scanner. It will support
all clinical applications currently supported by the LightSpeed product line.
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© 2005 General Electric Company. All rights reserved.
11-3
LightSpeed ™ 4.X
The distinguishing feature of LightSpeed 4.X is the ability to simultaneously collect 16 rows
of scan data (as opposed to 1 row with HiSpeed CT/i. This 16-row data collection is
accomplished via a 24-row detector and a 16-row DAS (Data Acquisition System).
The detector/DAS combination will provide functionality unmatched by any CT scanner in
the world.
System Characteristics
•
World’s first 16-row CT scanner and 16-row detector.
•
LightSpeed 4.X optional variable rotation scan speeds (0.5, 0.6, 0.7, 0.9).
•
Helical acquisitions at significantly faster table speeds.
•
Potential for new applications due to faster coverage and fewer tube cooling delays.
•
The ability to generate 16 axial images per gantry revolution.
•
Every system EMC compliant with improved reliability and uptime.
•
World-class User Interface: CT/i continuum.
Tube
Performix tube, common tube with HiSpeed CT/i.
Detector
•
24 rows in Z axis = 24 physically separated cells in Z
(HighSpeed CT/i = single cell).
•
Detector cell segregation in Z provides post-patient collimation.
•
2.19mm actual detector cell size in Z.
•
1.25mm effective cell size in Z at ISO center — Outer 8 rows
•
0.625mm effective cell size in Z at ISO center — Inner 16 rows.
•
16 data rows output.
•
Cells summable in Z by FET array to provide various slice thickness.
•
Cell summation combinations include:
– 4 x 3.75mm
– 8 x 2.5mm
– 8 x 1.25mm
– 16 x 0.625mm
– 16 x 1.25mm
•
11-4
Integrated, permanently bonded flex connectors.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
General Information
Scalable Data Acquisition Sub-System (MDAS)
•
16 rows input from detector.
•
16 rows output to SRU (Scan Reconstruction Unit).
•
Supported by 96 interchangeable converter (CNVT) cards.
•
256 input channels/converter card MDAS.
•
31-gain, integrating, front-end pre-amp.
•
Supports 1640 Hz sampling.
•
Forward error correction applied to output data.
•
Control functions:
– Detector FET array and heater control.
– Error detection and reporting.
Patient Scanning
LightSpeed 4.X uses a “shorter” geometry than HiSpeed CT/i. Since X-Ray intensity varies as
the square of the distance, the benefit of the Lite geometry, measured at ISO center, is:
(630/541)2 = 1.36 = 36% better X-Ray flux utilization. It also reduces the centrifugal force on
the tube which will allow for future faster rotational speeds.
Parameter
LightSpeed 4.X
HiSpeed CT/i
ISO Height
1015mm
1092.9mm
Focal spot to ISO
541mm
630mm
Focal spot to det
949mm
1100mm
SFOV
496.9mm
480mm
Bore
700mm
700mm
EMI/EMC
All systems built to global regulatory emissions (EMC) and immunity (EMI) compliance
standards to improve reliability, uptime and performance in its intended environment.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
11-5
LightSpeed ™ 4.X
Network
Remote Host Parameters
The LightSpeed 4.X Network function has new enhancements to support DICOM networking.
When adding or updating a remote list, there are some new parameters needed. All of the
following information, except for Comments, needs to be provided in order to set up a
remote host:
•
The Host name to be entered is the name of the device. If the device is DICOM, the name
must match exactly to the name given to the device.
•
The Network address of the device is provided by the institution’s network administrator.
•
The Network protocol consists of two choices: Advantage NET or DICOM. If the
LightSpeed 4.X will be sending to this device, the device must be DICOM and the DICOM
network protocol must be selected. If this device is a GE Advantage Genesis system, you
must select the Advantage NET network protocol to send to the LightSpeed 4.X.
NOTE: Advantage Net is not available on PC based systems.
•
The Port number is unique to the device. If the device is an Advantage Windows
workstation or HiSpeed CT/i, X/i, or NX/i system, the number will be 4006.
•
The AE Title is unique to the device. If the device is an Advantage Windows workstation
or another GE Medical Systems system, the AE Title will be the same as the Host name.
•
The Comment field allows you to input a comment.
•
The Archive Node refers to the archiving responsibility of the device:
– If Auto is selected, the CT system will automatically check to see if the device is a
Storage Commitment Provider.
– If Yes is selected, the device will be responsible for archiving images. When the device
has received and saved the images, a notification message will be displayed on the
scanner console and the Archive status for the exam will be ’A’ for archived.
– If No is selected, the device will not be responsible for archiving.
NOTE: The device must be a Storage Commitment Provider in order for remote archive node
to function.
11-6
•
Access to the local host refers to the device’s ability to access the LightSpeed 4.X. Select
Yes if you want the device to be able to send to and/or query the LightSpeed 4.X.
•
The Custom search feature enables the Custom search dialog box to be automatically
displayed when you select receive from the remote browser. If Yes is selected, the
feature is enabled. If No is selected, the Custom search dialog box will not automatically
be displayed. You can, however, get to the search feature once the remote browser is
displayed, by simply selecting Search, on the remote browser.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
General Information
Network Compatibility
The LightSpeed QX/i, Plus, and Ultra image format is DICOM. This image format may only be
transferred between systems using a DICOM network protocol. The receiving station must
support DICOM receive for LightSpeed images to be transferred (send or receive) to it.
Use the following table for network compatibility. The table lists the network protocol to use
and the features available for that system. The far left column lists the system the user is at
(from).
From
To
LightSpeed
QX/i, Plus,
or Ultra
To
HiSpeed
CT/i
To
HiSpeed
Advantage
To
CT IC
To
HiSpeed
NX/i, X/i, or
QX/i
To
Party
DICOM
Station
3rd
LightSpeed
QX/i, Plus, or
Ultra
DICOM
Query
Send
Receive
DICOM
Query
Send
Receive
Advantage
Query
Receive
Advantage
Query
Receive
DICOM
Query
Send
Receive
DICOM*
Query**
Send
Receive**
HiSpeed
CT/i
DICOM
Query
Send
Receive
DICOM
Query
Send
Receive
Advantage
Query
Send
Receive
Advantage
Query
Send
Receive
DICOM
Query
Send
Receive
DICOM*
Query**
Send
Receive**
HiSpeed
Advantage
Advantage
Send
Advantage
Query
Send
Receive
Advantage
Query
Send
Receive
Advantage
Query
Send
Receive
Advantage
Send
DICOM
Send
CT IC
Advantage
Send
Advantage
Query
Send
Receive
Advantage
Query
Send
Receive
Advantage
Query
Send
Receive
Advantage
Send
DICOM
Send
HiSpeed
FX/i, DX/I,
LX/i
DICOM
Query
Send
Receive
DICOM
Query
Send
Receive
Advantage
Query
Receive
Advantage
Query
Receive
DICOM
Query
Send
Receive
DICOM*
Query**
Send
Receive**
3rd Party
DICOM
Station
DICOM
Query
Send
Receive
DICOM
Query
Send
Receive
DICOM
Query
Receive
DICOM
Query
Receive
DICOM
Query
Send
Receive
DICOM*
Query**
Send
Receive**
NOTE: Some 3rd party stations use the ODINA network protocol. In this case use DICOM
protocol and port number 104
NOTE: ** Query capability is only available only if station is a query retrieve provider.
NOTE: LightSpeed16, Ultra, Plus, QX/i, or HiSpeed QX/i PC based systems do not support
Advantage Network Protocol.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
11-7
LightSpeed ™ 4.X
From
To
AW 1.2
To
AW 2.0
To
AW 3.10
To
AW 4.
To
LightSpeed
QX/i, Plus,
or Ultra
LightSpeed
QX/i, Plus,
or Ultra
DICOM
Send
DICOM
Send
DICOM
Send
DICOM
Query
Send
Receive
DICOM
Query
Send
Receive
AW 1.2
SDC Net
Query
Send
Receive
SDC Net
Query
Send
Receive
SDC Net
Query
Send
Receive
SDC Net
Query
Send
Receive
DICOM
Query
Send
Receive
AW 2.0
SDC Net
Query
Send
Receive
SDC Net
Query
Send
Receive
SDC Net
Query
Send
Receive
SDC Net
Query
Send
Receive
DICOM
Query
Send
Receive
AW 3.1
SDC Net V1
Query
Send
Receive
SDC Net V2
Query
Send
Receive
SDC Net V3
Query
Send
Receive
SDC Net
Query
Send
Receive
DICOM
Query
Send
Receive
AW 4.0
SDC Net
Query
Send
Receive
SDC Net
Query
Send
Receive
SDC Net
Query
Send
Receive
SDC Net
Query
Send
Receive
DICOM
Query
Send
Receive
NOTE: Advantage Windows systems do not support Query Retrieve provider. Send images
from the Advantage Windows to the LightSpeed QX/i, LightSpeed Plus, or LightSpeed
Ultra.
NOTE: LightSpeed16, Ultra, Plus, QX/i, or HiSpeed QX/i PC based systems do not support
Advantage Network Protocol.
11-8
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
General Information
System Data and Control Flow
3c
Table
Controller
Data Flow
5
3b
3a
Stationary
Controller
Control Flow
Generator
On-Board
Controller
Performix
Tube
3e
Cam
Collimator
6
Real-Time Control Flow
4
4
3d
Slip Ring
2
7
+
UIF Monitor
16 Row Detector
8
1
Host
Computer
SRU
10
MDAS
9
9
Keyboard
Component
Functions
Data and Control Flows
Host
Computer
User interface, image
display
1. Scan and recon prescription from
operator
SRU
Scan and recon control
and Image generation
2. Scan prescription to “master” controller
Stationary
Controller
On-Board
Controller
Table
Controller
Slip-ring
Stationary base real-time
control and “master”
controller
Rotating base real-time
control
Patient table real-time
control
Signal and power transfer
between stationary and
rotating components
3. Scan parameters distributed
a) table position
b) rotating parameters
c) kV and mA selections
d) X-Ray beam collimation and filter
selections
e) detector slice thickness and SDAS
gain selections
4. Real-time control signals during
scanning
5. High voltage
Generator
High voltage generation
6. Un-collimated X-Ray beam
Performix
Tube
X-ray generation
7. Collimated X-Ray beam
Cam
Collimator
Formation of the X-Ray
beam
8. Analog scan data
24-row
Detector
Conversion of X-Ray to
analog signal data
9. Digital scan data
MDAS-16
Conversion of analog
signal data to digital data
10. Patient images
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
11-9
LightSpeed ™ 4.X
X-ray Generation and Detection Details
Overview
The distinguishing feature of LightSpeed 4.X is the capability to simultaneously collect
multiple rows of scan data.
Gantry Coordinate System
X, Y, Z: Scanner gantry coordinate system:
•
X = Tangent to circle of rotation.
•
Y = Radial (from ISO toward tube focal spot).
•
Z = Longitudinal (in/out of the scan plane).
X
X-Ray Tube Focal Spot
Y
ISO
Z
Scan Plane
Patient Table
11-10
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© 2005 General Electric Company. All rights reserved.
General Information
Components
Figure 11-1 X-Ray Generation and detection components viewed from side of gantry
Anode/Target
Performix Tube
Cathode
Bowtie
Uncollimated X-Ray Beam
Cam Collimator
Tungsten Cams
Front of Gantry
Collimated X-Ray Beam
LightSpeed 3.X Detector =
Continuous Collimator +
57x16 Row Detector Modules
Detector Collimator
16 Individual Lumex Cells
FET Array
Integrated Flex:
16 Columns x
2 Macro Rows =
32 Signals/flex
Z
CAM Collimator
The pre-patient collimation of the X-Ray beam is accomplished via 2 independently
controlled tungsten cams (see Table 11-2 on page 11).
Figure 11-2 Cam Collimator Examples
Focal Spot
Offset
Cam Offset
Beam Offset
Wide Beam
Centered
Narrow Beam
Centered
Narrow Beam
Cams Offset in Z
e.g., 4x5mm Slices
or
8x2.5mm Slices
e.g., 4x1.25mm Slices
e.g., 4x1.25mm Slices
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
Offset used to compensate for
Z axis beam offset.
11-11
LightSpeed ™ 4.X
Z-Axis Cell Summation
The LightSpeed 4.X detector is segmented into cells in the Z dimension, providing
post-patient collimation of the X-Ray beam. This post-patient collimation is provided by the
segmentation of the detector cells, and not by a separate post-patient collimator as some
CT systems use.
The post-patient collimation, along with summation of cells in the Z direction by the detector
FET array, determines the Z-axis slice thickness of the scan data.
The Z dimension extent of each cell are 0.625mm at ISO center for the center 16 rows and
1.25mm for the outer 8 rows.
1, 2, 3 or 4 cells are summed in Z to produce a “macro cell.” All macro cells in the same Z
plane form a “macro row.” A macro row consisting of a single cell in each column produces
scan data with thickness of either 0.625mm or 1.25mm at ISO center (see Table 11-3 on
page 12). A macro row consisting of summed cells in each column produces scan data with
varied thickness at ISO center (see Table 11-3 on page 12). The 16 macro rows are labeled
8A, 7A, 6A, 5A, 4A, 3A, 2A, 1A, 1B, 2B, 3B, 4B, 5B, 6B, 7B, and 8B. 8A is closest to the patient
table. Each flex transmits 8 macro cells to the DAS per column x 16 columns per detector
module = 128 data channels per flex (see Table 11-1 on page 11).
Figure 11-3 Channel Summation in Z - Examples
Tungsten Cams
10mm Collimation
Patient Table
16x1.25
16x0.625
8A, 7A, 6A, 5A, 4A, 3A, 2A, 1A
1B, 2B, 3B, 4B, 5B, 6B, 7B, 8B
Tungsten Cams
10mm Collimation
Patient Table
8A, 7A, 6A, 5A, 4A, 3A, 2A, 1A
1B, 2B, 3B, 4B, 5B, 6B, 7B, 8B
Tungsten Cams
20mm Collimation
Patient Table
8x2.5
8x1.25
4A, 3A, 2A, 1A
Tungsten Cams
20mm Collimation
Patient Table
1B, 2B, 3B, 4B
4A, 3A, 2A, 1A
1B, 2B, 3B, 4B
Collimator Theory
The purpose of tracking is to follow the focal spot so that we can keep the uniform X-ray of
the narrowest possible beam on the detector to reduce dose and still avoid artifacts.
The focal spot moves in Z due to thermal changes in the tube and a mechanical forces
during gantry rotation and tilt angle.
Each cam is basically an independent system.
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General Information
What
Whatdoes
doestracking
trackingdo
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focal
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Collimator Control
Collimator Control
Board (CCB)
Board (CCB)
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steady
1 measure position of X–ray beam
1 measure position of X–ray beam
22compute
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newcollimator
collimatorposition
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33move
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collimatortotofollow
followthe
thefocal
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channelsthat
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DAS Control Board
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wwFast
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In the Hi Res mode (1i x x1.25 mode) the collimator
projects an x–ray beam on a single 1.25 mm detector row.
Only 1 image per rotation is generated at the lowest
possible single slice dose.
AutomA Theory
Automatic tube current modulation: Tube current modulation is a technical innovation that
significantly reduces radiation dose. The concept is based on the fact that pixel noise in a
CT image is attributable to the X-ray quantum noise in the projections. By adjusting the tube
current to follow the changing patient anatomy, the quantum noise in the projections can
be adjusted to maintain a desired noise in the image and to improve dose efficiency.
AutomA (Z-axis modulation) adjusts the tube current to maintain a user selected quantum
noise level in the image data. It regulates the noise in the final image to a level desired by
the user. In this sense, AutomA is the CT equivalent of the auto exposure control systems
employed in conventional X-ray systems. AutomA attempts to make all images have similar
x-ray quantum noise independent of patient size and anatomy. Dose is reduced with
AutomA protocols vs. fixed mA protocols, since the tube current will be automatically
reduced for smaller patients and anatomic regions. With AutomA, the tube current
modulation is determined from the attenuation and shape of scout scan projections of the
patient just prior to CT exam sequence.
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LightSpeed ™ 4.X
Angular modulation has a different objective than Z-modulation. It adjusts the tube current
to minimize X-rays over angles that have less importance in reducing the overall image
noise content. In anatomy that is highly asymmetric, such as the shoulders, x-rays are
significantly less attenuated in anterior-posterior (AP) direction than in the lateral direction.
Thus, the overwhelming abundance of AP x-rays can often be reduced very significantly
without a significant effect on overall image noise.
Angular modulation was first introduced on GE single slice scanners in 1994 and is currently
being developed for the LightSpeed scanners.
1 L. Kopka and M. Funke, "Automatically adapted CT tube current: Dose reduction and image quality in phantom
and patient studies," Radiology 197 (P) , 292 (1995) .
2. D. R. Jacobson, W. D. Foley, S. Metz, and A. L. Peterswen, "Variable milliampere CT: Effect on noise and low
contrast detectability," Radiology 210(P), 326 (1996)
AutomA Theory
AutomA is an automatic exposure control system that employs Z axis tube current
modulation. A noise index parameter allows the user to select the amount of X-ray noise
that will be present in the reconstructed images. Using a single patient scout exposure, the
CT system computes the required mA to be used during each gantry rotation based on the
selected noise index setting. The noise index value will approximately equal the standard
deviation in the central region of the image when a uniform phantom is scanned and
reconstructed using the standard reconstruction algorithm.
The system determines the tube current using the patient's scout projection data and a set
of empirically determined noise prediction coefficients for a reference technique. The
reference technique is the selected kvp, and an arbitrary 2.5 mm slice at 100 mAs for an
axial reconstruction using the standard reconstruction algorithm. The scout projections
contain density, size and shape information about the patient. The total projection
attenuation (projection area) contains the patient density and size information and the
amplitude and width of the projection contains the patient shape information. These patient
characteristics determine how much x-ray will reach the detector for a specified technique
and hence determine the image standard deviation due to x-ray noise for a given
reconstruction algorithm.
To predict the image noise at a given z position for the reference technique, the projection
area and oval ratio are obtained from the patient's scout. The oval ratio is an estimate of the
patient asymmetry that is determined from the amplitude and width of the projection data.
The expected x-ray noise for the reference technique (reference noise) is then calculated as
a function of the projection area and oval ratio using polynomial coefficients that were
determined by a least squares fit of measurements for a set of phantoms representing a
clinical range of patient sizes and shapes.
Knowing the reference noise and the difference between the reference technique and the
selected prescribed technique, the mA required to obtain the prescribed noise index is easily
calculated using well know equations from x-ray physics. That is, the noise is inversely
related to the square root of the number of photons and the number of photons is
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General Information
proportional to the slice thickness, slice acquisition time, and mA. In the GE Automa design,
an adjustment factor for helical pitches is also incorporated in the calculation to account for
noise differences that scale between helical selections and the axial reference technique.
Understanding AutomA Behavior
1. Why is the standard deviation I measure in the image some times different than the
noise index I selected for the scan?
There are many factors that can account for this. But, first consider that the noise index
setting you make only adjusts the tube current so that the system projects a similar X-ray
intensity through the patient to the detector. Hence it regulates the X-ray noise or quantum
noise in the projection data. The noise in the image depends on other factors as well. The
reconstruction algorithm selection, reconstructed slice thickness selection (if different than
your prospective selection), and the use of image space filters will also change the noise in
the image. In addition, it is very difficult to make standard deviation measurements on
patient data since the standard deviation is affected by small CT number variations of the
anatomy and by patient motion or beam hardening artifacts. Even with uniform phantoms,
standard deviation measurements will produce some variability in measured results
because of the inherent nature of quantum statistics.
Another situation that can cause significant differences between the selected noise index
and the image standard deviation is when very large patients provide insufficient detector
signal. In these cases, electronic noise sources can become the dominant image noise
source instead of X-ray noise. In these cases at various threshold levels, special projection
data dependent filters begin to be applied to help preserve image quality. The highest kvp
should always be used when excessively large patients are to be scanned.
2. Will I get a dose reduction when I use automA?
AutomA will use a dose that depends on the noise index you select and the size of the
patient you are scanning. If you do not obtain a dose reduction, you may have selected a
lower noise index than you really need and this is resulting in higher mA values on average
than your fixed mA protocols. One strategy to avoid using more dose is to set the max mA
parameter to the same level as your fixed mA protocols. This will cap the maximum dose to
your previous fixed mA protocol. Hence, automA will never be allowed to use more dose
then you previously used. However, automA will decrease dose for those patients and
regions where the selected noise index can be maintained with decreased mA. Note that,
image noise will increase in regions where the mA is limited by the max mA range but the IQ
would be no different that with the fixed mA results.
3. Why do my images seem noisier when I use automA?
AutomA will produce an x-ray intensity to maintain the noise index you select. Thus, you
may need to use a lower noise index. This may be the case if you find that the average mA
for your population of patients is generally lower than your previous fixed mA protocols.
Note that this would mean you are using less dose and hence higher noise would be
expected.
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LightSpeed ™ 4.X
Certain patient images may also be noisier than your experience suggests. For example,
your experience tells you to expect significantly lower noise in thin patients than obese
patients. Since automA makes the image noise approximately the same for all patients, you
may have to re-learn what to expect. What is most important, is to find the highest noise
index that allows you to make a confident diagnosis for the clinical problem since this
results in the lowest patient dose. One would generally expect that all patients, regardless of
size, will require about the same image noise for a similar clinical diagnostic problem. If you
find the noise is too high, there are several strategies you can use.
A conditional noise limiting strategy you can employ, is to increase the low mA range
parameter. If you find that images are generally not acceptable to you below some
minimum mA value, then you may set this value as the low mA range limit. This will prevent
automA from using lower mA values than you desire. Note, however, that this overrides the
purpose of automa and causes the image noise to decrease below the selected noise index
and thereby increases the dose.
Yet another possibility for higher noise than you might expect is if you are looking at
multiple reconstructed images that have thinner slices than the prospective scan Rx slice
thickness. AutomA uses prospective slice thickness as a factor when the mA table is
generated. You need to be sure the prospective image parameters are set for the primary
images you will be using. This caveat applies equally for fixed mA as well as automA
scanning.
Higher noise images can also occur when patients are not well centered in the scan field of
view. The bowtie filter attenuation increases with distance away from isocenter. Hence the
thickest part of the patient should be approximately centered in the scan field of view.
Otherwise image noise will increase since the patient thickness adds to the bowtie filter
thickness. This is especially important for highly asymmetric anatomy such as through the
shoulders. Again, this effect is no different with automA than with fixed mA.
Recognize also that there are also some obese patients that exceed the capabilities of the
tube and generator to satisfy the selected noise index. This is also no different than fixed mA
scanning. For such obese patients, one strategy is to select a higher kv setting when
possible.
4. Why is the mA that is annotated on the image sometimes slightly different than the
mA I see in the mA table?
The mA displayed on the image is determined by measuring the generator mA during the
scan and averaging the measured result over the total number of views used to reconstruct
the image. The number of views used to produce the image may be more than one gantry
rotation for a helical scan. Hence the annotated value is a combination of the mA table
values that depends on how many views from each rotation were used for the image. In
addition, the generator is automatically adjusting the filament current to account for
changing conditions during the scan to keep the mA within the desired tolerance of the
commanded mA table. For example, this is why you could see an mA value of 41 in the
image where the mA table indicated 40.
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General Information
5. I understand that noise in the image noise changes with reconstruction parameter
selections, but why is the noise sometimes different when I retro reconstruct the
same scan data at a different display field of view?
When you select a reconstruction algorithm, the system may sometimes re-adjust the
actual filter kernel. This readjustment will change the image noise. This will happen if the
display field of view selection exceeds a certain size and is especially apparent with higher
resolution algorithms such as bone and edge. The change in kernel is required when the
DFOV selection makes the pixel size too large to support the intended spatial resolution. This
characteristic is independent of automA.
System Operational Modes
Overview
The LightSpeed 4.X scanner provides unique data collection functionality unmatched by
any competitor’s system. Even with this powerful data collection capability, the basic
modes of operation presented to the user will remain unchanged from HiSpeed CT/i:
•
Scout
•
Axial
•
Helical
•
Cardiac Helical
•
Cine
Scout
Scout imaging is used for anatomical location in conjunction with scan and recon
prescription, to provide an anatomical cross-reference for axial images, and to provide quick
feedback to the user as to the anatomy scanned. Scout supports the following features:
•
Less than 10 second reconstruction.
•
All kV and mA stations available, dependant on generator and tube limitations.
•
1.25mm resolution in Z.
•
100mm/sec table speed (75mm/sec @ HiSpeed CT/i).
•
Data collected in 4 x 1.25mm mode. Reconstruction algorithms “combine” data to
maintain 1.25mm resolution in Z.
Pediatric Imaging
Adult techniques and protocols should not be used on pediatric patients (under 2 years of
age.)
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LightSpeed ™ 4.X
Axial
Axial scanning is expected to be used less on LightSpeed 4.X than on HiSpeed CT/i. The goal
for LightSpeed 4.X is to support virtually all applications using helical scanning. There may
be applications, such as high-resolution Inner Auditory Canal (IAC) or lungs, where axial
scanning is required for image quality reasons.
Axial and Cine imaging features include:
•
All kV and mA stations available, dependant on generator and tube limitations.
•
Scan speeds: 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 2.0, 3.0, 4.0seconds.
Cine: 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 seconds.
•
Variable image thickness.
•
Sample rates: 984 Hz, 1090 Hz, 1230 Hz, 1400 Hz, 1640 Hz (984 Hz only @ HiSpeed CT/i)
•
Segmented reconstruction option for cine scans.
LightSpeed 4.X can acquire 16 axial slices in a single rotation when the 16 slice scanning
option is installed. These slices can be reconstructed independently to produce 16 images.
These images may be combined to produce composite images. For example:
– Data collected in 16 x 1.25 mode
– (16i) 16 x 1.25 images
– (4i) 4 x 5.00mm images
– (2i) 2 x 10.00mm images
Helical
Helical Overview
The 24-row detector and 16-row DAS provide the greatest benefits when used in the helical
mode. In the helical mode, data from 16 detector rows is selectively combined and weighted
during reconstruction in order to achieve the optimal balance between image z-axis
resolution, noise, and helical artifacts.
Helical imaging features include:
•
All kV and mA stations available, dependant on generator and tube limitations.
•
120 second maximum helical scan time.
•
Pitches:
NOTE: Beginning with the LightSpeed 4.X M3.1 release, the user interface has changed the
scan mode names. These new names indicate pitch as expressed by the ratio of table
travel per rotation to beam collimation. The new scan mode name designation will
be indicated on image annotation.
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General Information
Previous Scan Mode
Designator
Scan Mode
HQ
HQ
HS
UQ
UM
UF
US
1:1
0.75:1
1.5:1
0.625:1
0.875:1
1.35:1
1.675:1
•
Variable image thickness (recon parameter).
•
Sample Rates: 984 Hz, 1090 Hz, 1230 Hz, 1400 Hz, 1640 Hz
•
Segmented reconstruction option.
•
0.1mm minimum incremental retrospective recon image spacing.
Once the LightSpeed 4.X helical data is collected, it can be reconstructed at image thickness
greater than or equal to 1x the detector macro-row size. Premium image quality (near axial
image quality) is achieved at 2x the detector macro-row size. The thinnest image thickness
possible, which has image quality slightly degraded from 1.5:1 pitch on HiSpeed CT/i, is 1x
the detector macro-row size.
Premium Image Quality Helical Example
Premium image quality (near axial image quality) is achieved as follows:
•
Detector macro-row size = 50% of the desired image slice thickness.
•
Pitch (table travel over deam collimation) = 0.625:1.
LightSpeed 4.X “Premium” IQ example for 8 slice mode:
•
5mm images
•
8 x 2.5mm detector mode
•
table speed of 6.25mm/rotation (0.5625:1)
LightSpeed 4.X “Premium” IQ example for 16 slice:
•
0.5625:1 mode
•
5mm images
•
16 x 0.625mm detector mode
•
5.625mm/rotation
Cardiac Helical Overview
A lower pitch helical scan is available for cardiac applications in conjunction with the CardIQ
SnapShot option. In this scanning mode, heart rate monitoring is performed during the
helical acquisition and the associated ECG gating information is stored with the scan data
such that a cardiac gated SnapShot reconstruction algorithm can be applied for prospective
and retrospective images. SnapShot reconstruction is used to minimize the motion of the
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LightSpeed ™ 4.X
heart in the resultant images. The pitch factor for the cardiac helical scan is determined by
the system and is a function of the patient heart rate.
Cardiac Helical imaging features include:
•
All kV and mA stations available, dependent on generator and tube limitations.
•
120 second maximum cardiac helical scan time.
•
Pitches: determined by system, ranging from 0.25 to 0.35, based on patient heart rate. A
higher heart rate will use a higher pitch factor.
•
Variable image thickness via acquisition slice thickness parameter only (0.625, 1.25, 2.5,
3.75, and 5.0mm). No image thickness recon parameter is available.
•
SnapShot Segment Burst and Burst+ and Segmented (non-gated) reconstruction
options.
•
Cardiac phase location parameter of 0 to 99% of R-to-R cycle.
•
0.1mm minimum incremental retrospective recon image spacing.
Once the cardiac helical data has been collected, it can be reconstructed at one or more
arbitrary heart cycle phase locations. Segmented reconstruction is also available
retrospectively if non-gated images are desired.
Calibration Modes
LightSpeed 4.X calibrations include:
•
Z-axis gain calibration - new for LightSpeed 4.X
•
Tube warm-up
•
Air calibration*
•
Phantom calibration*, upgrades for 50cm SFOV
•
Water Cal
•
IQ Cal check
* = similar to HiSpeed, upgraded for 16 row data collection
System Image Quality Features
“Lite” Geometry
The “Lite” geometry is common to the LightSpeed Plus and LightSpeed QX/i, HiSpeed X/i,
NX/i, and QX/i.
Benefits include:
11-20
•
Produces (630/541)2 = 36% better X-Ray flux utilization than HiSpeed CT/i due to the
fact that the focal spot is moved closer to the patient. For axial scanning, images can be
generated with the same noise as HiSpeed CT/i using only 74% of the mAs.
•
Reduce centrifugal force on the tube.
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General Information
Clever Gain
LightSpeed 4.X will eliminate overranging by:
•
Selecting a low enough gain so that the system does not overrange (31 gain DAS).
Scan and Recon Prescription User Interface (UIF)
All scan and recon options are clearly explained to the user.
Axial scan prescription describes various detector configuration, scan speeds, etc. Axial
recon prescription describe various recon slice thickness combinations and how these are
restricted by scan parameters.
LightSpeed 4.X helical scan and recon prescriptions are more challenging than axial.
LightSpeed 4.X helical scanning will be: 8 slice = 8 detector macro rows x 4 pitches and 16
slice LightSpeed 4.X helical scanning will be = 16 detector macro rows x 4 pitches. Once the
scan data is collected, the LightSpeed 4.X recon algorithms support image reconstruction at
image thickness of 1x to 8x the detector macro-cell size. Therefore, image slice thickness is
now a recon parameter and not a scan parameter. Desired image thickness must be taken
into account during scan parameter selection.
Current X-Ray Tube Capacity Effects Prescriptions and
Interscan Delays
The system provides prescription alternatives when:
•
Current prescription requires excessive prep, interscan, or intergroup delay.
•
Technique requirements exceed the prescribed delays.
Although the rotating anode increases the tube’s heat tolerance, it still has a physical limit.
The anode transfers its heat to the oil filled tube housing. The housing, in turn, dissipates
heat into the surrounding air.
The system keeps a running total of estimated tube heat. When you request scans during
Scan Prescription, the system estimates the number of heat units these scans will produce,
and compares this value with the running total.
If the prescription estimate exceeds the current capacity, the system displays a series of
prescription OPTIMIZE screens that recommend increased delays, alternative Scan Technic
settings, or offer to split the current scan group into smaller groups.
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LightSpeed ™ 4.X
Focal Spot
The X-Ray tube contains a small filament and a large filament. The small filament
concentrates the focal spot size, which improves spatial resolution but cannot tolerate high
technique. The large filament tolerates high technique but loses some of the small
filament’s spatial resolution.
The system automatically selects the small filament:
•
When the technique equals 24kW, or less.
The system automatically selects the large filament:
•
When the technique exceeds 24kW.
Example: Reduce mA setting from 210mA to 200mA (120kV) to enable Small Filament.
Filament Selection
On traditional single-slice CT systems, such as HiSpeed CT/i, the filament selection effects
the slice thickness for thin slices scanning, with a larger filament producing a larger effective
slice thickness. The LightSpeed 4.X has eliminated this effect, and true thin slice imaging can
be achieved using both the small and large filament.
Filament Selection Table
In order to provide the best image quality, and maximize patient throughput, the LightSpeed
4.X system bases the automatic filament selection upon the following table:
Performix Tube
Small Filament
All Algorithms
Large Filament
All Algorithms
80 kV
10 to 300 mA
> 300 mA
100 kV
10 to 240 mA
> 240 mA
120 kV
10 to 200 mA
> 200 mA
140 kV
10 to 170 mA
> 170 mA
Data Collection
The detector and MDAS assembly mounts opposite the X-Ray tube on the rotating base. The
X-Ray beam leaves the X-Ray tube, passes through the gantry opening, and enters the
detector. Any material (patient or phantom) positioned within the gantry opening absorbs or
deflects the weaker X-Ray photons. The numbers of photons that enter the detector
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General Information
depends upon the intensity of the X-Ray beam and the density of the material in the gantry
opening. An increase in density causes a decrease in the number of photons that enter the
detector.
The revolutionary new LightSpeed detector allows 16 rows of data to be collected at a time
for both axial and helical imaging. This allows 16 axial images to be generated in a single
gantry rotation in the axial mode. This allows helical images to be taken at faster speeds,
and with lower power, than single slice scanners.
The MDAS measures the detected X-Ray at regular time intervals, called views, and
transmits the information to the image reconstructor for reconstruction into a display
image. The total degrees of gantry rotation and the scan time determine the number of raw
views per image.
For scans greater than 1 second, the raw views are summed together before image
reconstruction. This allows the system to maintain constant image reconstruction times and
spatial resolution/aliasing for all scan speeds. (Note that image reconstruction of more raw
views reduces aliasing at the expense of reconstruction time.)
Example: A 1-second and a 4-second scan both gather data over 360 degrees, so both
scans reconstruct the same number of views per image. A segmented reconstruction uses
data acquired over 235 degrees, so it reconstructs fewer views per image.
Scan Parameters
Scan Choice
Determines:
kV
X-Ray energy intensity and calibration data used
mA
X-Ray dose
Scan Time and
Interscan Delay
Length of scan rotation in seconds; length of delay in
seconds between exposures
Scan Rotation
(normal scan, partial scan)
Degrees of scan rotation during data collection (X-Ray
on)
Gantry Tilt
Angle X-Ray travels through patient
Spacing
Z-Axis distance between scan centers
Thickness
Width of image
Azimuth
X-Ray tube location during scout scan
SFOV - Scan Field of View
Centimeters of data available, and any special
processing applied or available, for image
reconstruction.
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LightSpeed ™ 4.X
Reconstruction
The scanner compares the collected data with the calibration data then converts the
detector channel views into a two dimensional matrix. The system converts each matrix
element (pixel) into a CT number. The system displays a scout image as it acquires the data,
but an axial image will be displayed after reconstruction is completed. The axial and scout
images take approximately three seconds to reconstruct.
Your choices control the image outcome. Choose parameters to enhance or tailor the
acquisition and processing to the anatomy of interest. Select scan technique and image
parameters that provide optimum resolution.
The system has disk space for 2,900 1-second scan rotations. The system stores the most
recent scan data in the oldest scan file with an unreserved status. The system continually
overwrites the scan files with data.
NOTE: If you plan to reconstruct images, you must use files that reside in the disk. Either
reserve the scan files you plan to retrospectively reconstruct, or reconstruct unsaved
scan files before the system overwrites the files with new scan data. The system
refuses to overwrite reserved scan files. Remember to release the reserved scan files
when you finish retrospective reconstruction.
Helical Scan Data Usage
In general, every data channel will contribute to at least one image during helical image
reconstruction. Some data channels are not used at the very beginning and end of the
helical scan due to the physics of multi-slice scanning and helical view weighting
algorithms.
During helical image reconstruction, some data channels in the middle of the helical scan
are not used if the image interval prescribed is GREATER THAN the values listed in the table
below.
For example, all data channels will be used for 1.25mm images, 0.5625 pitch, if the image
interval is less than or equal to 1.24mm.
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General Information
Channel Utilization Table - Full Modes
Scan Mode
Helical
Pitch
Table
Speed
(mm/rot)
0.563:1
5.625
11.25
9.375
18.75
13.75
27.5
17.5
35.0
6.25
12.5
8.75
17.5
13.5
27.0
16.75
33.5
0.938:1
1.375:1
1.750:1
0.625:1
0.875:1
1.350:1
1.675:1
Detector
row
collimation
(mm)
0.625
1.25
0.625
1.25
0.625
1.25
0.625
1.25
1.25
2.5
1.25
2.5
1.25
2.5
1.25
2.5
Image Thickness
0.63m
m
1.25m
m
2.5mm
3.75m
m
5.0mm
0.62
2.18
1.62
2.27
1.87
2.57
2.49
2.58
2.49
1.24
4.06
4.48
4.24
4.73
4.53
5.34
4.54
5.34
4.45
2.49
4.38
2.49
6.24
4.99
4.97
4.97
5.92
6.35
6.14
6.73
6.47
7.32
6.44
7.33
6.80
6.78
6.94
6.79
7.18
9.47
6.33
9.60
7.85
8.20
8.17
8.59
8.48
9.36
8.47
9.21
5.74
11.03
5.74
11.04
7.23
11.69
7.81
9.43
0.93
1.24
1.24
1.24
2.50
2.49
7.5mm
10mm
12.08
15.70
12.27
16.33
13.16
16.96
12.88
8.10
15.70
8.11
15.70
9.60
14.98
9.57
14.64
16.93
10.60
16.72
10.61
16.72
11.98
14.02
11.92
13.96
7.5mm
10mm
14.20
18.57
14.71
19.46
15.34
19.31
15.29
10.79
15.46
10.80
15.95
12.98
15.83
13.04
15.52
20.03
12.72
18.09
12.73
17.73
13.86
16.60
13.91
16.75
Channel Utilization Table - Plus Modes
Scan Mode
Helical
Pitch
Table
Speed
(mm/rot)
0.563:1
5.625
11.25
9.375
18.75
13.75
27.5
17.5
35.0
6.25
12.5
8.75
17.5
13.5
27.0
16.75
33.5
0.938:1
1.375:1
1.750:1
0.625:1
0.875:1
1.350:1
1.675:1
Detector
row
collimation
(mm)
0.625
1.25
0.625
1.25
0.625
1.25
0.625
1.25
1.25
2.5
1.25
2.5
1.25
2.5
1.25
2.5
Image Thickness
0.63m
m
1.25m
m
2.5mm
3.75m
m
5.0mm
1.30
2.66
2.68
2.73
3.41
3.07
3.97
3.04
4.02
2.24
4.76
5.22
4.98
5.60
5.34
6.20
5.28
6.22
6.17
4.67
4.72
4.84
6.45
7.35
6.42
7.93
7.00
7.48
7.36
7.91
7.64
8.47
7.65
8.50
8.24
8.35
8.47
8.48
9.25
9.99
9.29
10.18
9.28
9.65
9.48
10.10
9.66
10.73
9.76
10.71
10.23
11.47
10.24
11.22
10.61
13.47
10.67
13.28
1.65
1.98
1.96
2.36
3.87
3.97
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© 2005 General Electric Company. All rights reserved.
11-25
LightSpeed ™ 4.X
Nominal Helical Slice Thickness
Because the data for a helical image is weighted over more than one rotation, to provide the
best possible image quality the nominal image slice may differ slightly from the user
selection, dependent on table speed, pitch and slice selection. The nominal FWHM slice
widths are given in the following table.
Slice Thickness Table — Full Modes
Selected Slice
Scan
Mode
Table
Speed
(mm/rot)
0.63mm
1.25mm
2.5mm
3.75mm
5.0mm
7.5mm
10.0mm
Axial
N/A
0.60
1.09
2.34
3.75
4.84
7.35
9.84
Helical
0.563:1
5.625
0.63
1.25
2.50
3.75
5.00
1.25
2.50
3.75
5.00
7.50
10.00
Helical
0.938:1
9.375
1.25
2.50
3.75
5.00
1.6
2.50
3.75
5.00
7.50
10.00
Helical
1.375:1
13.75
1.25
2.50
3.75
5.00
1.60
2.50
3.75
5.00
7.50
10.00
Helical
1.750:1
17.5
1.25
2.50
3.75
5.00
35.0
1.60
2.50
3.75
5.00
7.50
10.00
Helical
0.625:1
6.25
1.25
2.50
3.75
5.00
7.50
10.00
2.50
3.75
5.00
7.50
10.00
Helical
0.875:1
8.75
2.50
3.75
5.00
7.50
10.00
2.50
3.75
5.00
7.50
10.00
Helical
1.350:1
13.5
2.50
3.75
5.00
7.50
10.00
3.20
3.75
5.00
7.50
10.00
Helical
1.675:1
16.75
2.50
3.75
5.00
7.50
10.00
3.20
3.75
5.00
7.50
10.00
11-26
11.25
0.85
18.75
0.80
27.5
0.85
12.5
1.25
17.5
1.60
27.0
33.5
1.70
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© 2005 General Electric Company. All rights reserved.
General Information
Slice Thickness Table — Plus Modes
Selected Slice
Scan
Mode
Table
Speed
(mm/rot)
0.63mm
1.25mm
2.5mm
3.75mm
5.0mm
7.5mm
10.0mm
Axial
N/A
0.60
1.09
2.34
3.75
4.84
7.35
9.84
Helical
0.563:1
5.625
0.75
1.50
3.00
4.50
6.00
1.50
3.00
4.50
6.00
9.00
12.00
Helical
0.938:1
9.375
1.50
3.00
4.50
6.00
1.90
3.00
4.50
6.00
9.00
12.00
Helical
1.375:1
13.75
1.50
3.00
4.50
6.00
1.90
3.00
4.50
6.00
9.00
12.00
Helical
1.750:1
17.5
1.50
3.00
4.50
6.00
35.0
1.90
3.00
4.50
6.00
9.00
12.00
Helical
0.625:1
6.25
1.50
3.00
4.50
6.00
9.00
12.00
3.00
4.50
6.00
9.00
12.00
Helical
0.875:1
8.75
3.00
4.50
6.00
9.00
12.00
3.00
4.50
6.00
9.00
12.00
Helical
1.350:1
13.5
3.00
4.50
6.00
9.00
12.00
3.00
4.50
6.00
9.00
12.00
Helical
1.675:1
16.75
3.00
4.50
6.00
9.00
12.00
3.00
4.50
6.00
9.00
12.00
11.25
1.0
18.75
1.0
27.5
1.0
12.5
1.50
17.5
2.00
27.0
2.00
33.5
Cardiac Helical Slice Profiles
Slice profile measurements for Cardiac helical scans are complicated by the fact that a
variable helical pitch is chosen based on the patient’s heart rate. For helical pitches greater
than 0.125, the full width half max of a slice collimated at 1.25 is approximately 1.6mm. The
full width half max of a slice collimated at 2.5mm is approximately 3.2mm.
When a pitch value significantly below 0.125 is chosen, the slice profile may vary
significantly from image to image in a single helical scan. The profile will depend on the
location of the prescribed image with respect to the detector locations. The variation in the
slice profiles can be understood by thinking of an axial scan. In an axial scan, an arbitrary
image location is not permitted. However, an attempt to create an image at an intermediate
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© 2005 General Electric Company. All rights reserved.
11-27
LightSpeed ™ 4.X
location could be performed by using data from adjacent detector rows. This would result in
an increased slice profile. As the pitch becomes much less than 2.0, the helical scan data
becomes more and more like axial scan data.
At a pitch of 1.4, for example, which is the prescribed pitch for a Cardiac Segment scan with
a patient heartrate of 60 bpm and gantry period of 0.5 sec, a 35% variation in the nominal
FWHM is possible.
Calibration Scans
Calibrations scans of air, and uniform objects called phantoms, provide the baseline
information the system needs to produce patient images. The system needs calibration
data for every possible combination of kV, detector row thickness, focal spot size, and scan
field of view.
Warm-up Required
Warm-up the tube:
•
Immediately before Cal Check.
•
Immediately before Calibration.
•
When the tube has cooled to the point that a warm-up is required to ensure optimal
image quality.
Data Storage
PC Based
The Console/Computer contains 36 gigabytes (Gb) of magnetic disk that records and retains
2900 1-second scan rotation files, a Reconstruction Processor that processes scan data into
image data, and a magnetic disk that stores CT specific scan software.
Octane Based
The Console/Computer contains 36 gigabytes (Gb) of magnetic disk that records and retains
2000 1-second scan rotation files, a Reconstruction Processor that processes scan data into
image data, and a magnetic disk that stores CT specific scan software.
Octane and PC based
The computer contains 73 gigabytes (Gb) of system disk that hold about 130,000
uncompressed 5122 image files, along with software.
Xtream based
The computer contains 2 73 gigabytes (Gb) of system disk that hold about 250,000
uncompressed 5122 image files, along with software.
11-28
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
General Information
Despite storage space, the system eventually runs out of disk space. If your facility plans to
preserve image data, you must periodically transfer images and scan information to the
designated archive media.
Image Display
Requested images pass through the IP (image processor) on their way to the CRT screen.
The Image Processor uses a bulk memory to store images selected for Auto View, MID,
paging, magnification, rotation, reformat or 3D (3D optional).
The images appear on the image monitor or CRT (cathode ray tube). The CRT screen
contains a display matrix of 1024 x 1024 picture elements, or 1,048,576 pixels. The 1024
display can be further divided into viewports. The number of viewports displayed determine
the number of pixels within a viewport. Each pixel displays one of the 256 available shades
of gray.
The LightSpeed 4.X system reconstructs axial and continuous images of 5122 pixels. Images
from other scanners may display 64, 128, 320, or 1024 pixel image matrices.
The amount of anatomy represented by each pixel equals the Display Field of View
diameter in mm divided by the matrix width/height.
The system assigns a unique CT number value, originally called a Hounsfield Unit, to each
pixel. The two dimensional pixel represents a three dimensional portion of patient tissue. The
pixel value represents the proportional amount of X-Ray beam that passed through
anatomy and entered the detector.
Gray Scale
The CRT translates the computed pixel value into a shade of gray. Your window Width and
Level choices control which range of CT values receive emphasis. The window Width assigns
the quantity of pixel values to the gray scale. The window Level determines the center pixel
value in the gray scale.
Possible range of pixel values
Width
Level
•
Window Width = selected range of pixel values
•
Window Level = middle value.
The system displays every pixel value that falls outside the gray scale as either black or
white. It assigns a gray value to every pixel that falls within the selected window. IF enabled,
the filmed image displays a gray scale icon along the left border of the image.
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© 2005 General Electric Company. All rights reserved.
11-29
LightSpeed ™ 4.X
The system displays the currently selected window Width and window Level along the
bottom of the screen: W = xxxxx and L = xxxxx. To determine the pixel values currently
represented by the gray scale: Divide the window Width by 2; add and subtract this number
to/from the window Level.
Example: W=320; L= -1500; 320 ³ 2 = 160
-1500 + 160 = -1340; -1500 - 160 = -1660
The gray scale represents values from -1340 to -1660
To find the best gray scale for an image, decrease the window width to 2. Increase or
decrease levels until the tissue of interest turns gray. Now increase the window width until it
includes the rest of the image.
CT Number
CT numbers range from -1024 to +3071. This system references CT number zero to water
and CT number -1000 to Air.
Lung and fat have negative pixel values and normally appear black. A CT number over 200
represents dense material like contrast agent, calcium, bone, and normally appears white.
Inverse Video reverses video white to black, but pixel values remain the same.
CAUTION:
CT Numbers are NOT absolute; misdiagnosis is possible. System and patient
variables may effect CT Number accuracy. If you rely solely upon CT numbers
without taking the following variables into consideration you could
misdiagnosis an image.
The following variables effect CT Number accuracy:
•
Partial volume effects of anatomy
•
Scans acquired with IV or oral contrast agents
•
X-Ray tube deterioration
•
Improperly calibrated system (poorly centered phantom, used wrong phantom,
replaced current calibration files with extremely old Cal files)
•
Beam hardening due to patient anatomy, especially bone.
To reduce CT Number variations:
11-30
•
Warm-up the X-Ray tube whenever the system recommends it; make sure the tube
design matches the software configuration parameters
•
Center the patient anatomy of interest in the gantry opening. Select an SFOV that
encompasses the patient.
•
Acquire comparable images with similar scan and reconstruction choices.
•
Maintain consistent table height throughout the exam.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
General Information
•
Test image quality on a regular basis to provide the numerical data to track system
performance over time.
To decrease the potential for misdiagnosis:
•
Use ROI to compare pathology to surrounding tissue
•
Scan structures with slice thicknesses about one-half the thickness of the lesion or less.
Example: Prescribe scan thickness of 5mm or less to scan a Lesion with a 10mm thickness.
(Display an axial image and use the Measure Distance and ROI functions to determine the
size of the pathology.
•
Center ROI measurements over the midpoint of the pathology to minimize partial
volume effects.
Variables You Cannot Control
The mixture of tissue types, such as fat with tissue within the same voxel (a pixel with depth),
varying patient sizes, differences between CT machines and X-Ray tubes, all lead to CT
number variance. In a well calibrated scanner, water has a CT number that ranges from –3
to +3. The CT number remains uniform across all kV settings. However, as the X-Ray tube
ages, kV decreases and pixel values become less dependable.
Pixels
The anatomic image consists of rows and columns of small, square, picture elements called
pixels. The CRT screen displays 1,048,576 pixels in a matrix of 1024 horizontal rows of 1024
pixels. Add number of viewports selected for viewing to determine the number of pixels used
for display in each viewport. The CRT screen pixel size remains the same, but the amount of
anatomy the pixels represent varies with the scan and display field of view (SFOV & DFOV). A
pixel also represents a specific anatomic area. The system identifies each two dimensional
pixel by its location, area and value.
Pixel Coordinates
Describe pixel location two ways.
•
Matrix Coordinates: Upper left pixel = (0,0);
lower right pixel = (511,511);
pixel in center of matrix = (255,255);
pixel ten columns to the right = (10,0)
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© 2005 General Electric Company. All rights reserved.
11-31
LightSpeed ™ 4.X
(0,0)
(511,0)
axial image
(0,511)
(511,511)
NOTE: The above illustration represents a 512 x 512 matrix viewport.
•
RAS: Anatomic distance from the center of the landmark slice
Target the image; decrease the DFOV diameter. Center the reconstruction on coordinates
other than the SFOV center.
Magnifying and targeting can displace the central SFOV pixel from the central CRT pixel.
Look at the DFOV coordinates and magnification annotation to find the SFOV center, or
display the grid. The grid always appears over the pixel in the center of the DFOV Matrix
(coordinate 255,255).
RAS Coordinates
These three distances in millimeters appear on the upper left of the viewport on which the
mouse cursor is on, when Continuous Report Cursor is selected.
•
The pixel with the R/L and A/P coordinates closest to zero, represents the SFOV center.
The S/I coordinate always equals the table location at isocenter.
S
A100.0
P
L
axial plane
R
A
R
1
0
0
.
0
axial image
L
1
0
0
.
0
P100.0
I
R 70 mm A 20 mm S 85.0
Coordinates transition from R to L, A to P, and S to I, to show relationships between current
location, landmark location, and isocenter.
•
11-32
Right: coordinate location falls to the patient’s right of the
mid-sagittal plane (right of isocenter)
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© 2005 General Electric Company. All rights reserved.
General Information
•
Left: coordinate location falls to the patient’s left of the
mid-sagittal plane (left of isocenter)
•
Anterior: coordinate location falls above the mid-coronal
plane (above isocenter)
•
Posterior: coordinate location falls below the mid-coronal
plane (below isocenter)
•
Inferior: scan location falls between the selected landmark
and patient’s feet.
•
Superior: scan location falls between the selected landmark
and patient’s head.
The DFOV and matrix determine pixel size.
A reconstructed pixel represents an area determined by dividing the Display FOV (in mm) by
the reconstruction matrix, squared. You may magnify pixels up to eight times the
reconstructed size, or minify them to one half size. The anatomic area represented by each
CRT pixel decreases as the magnification factor increases; anatomic area/CRT pixel
increases as the magnification factor decreases.
Pixel Size in millimeters
DFOV in cm
512 x 512
10
0.20
15
0.29
20
0.39
22
0.43
25
0.49
30
0.59
35
0.68
40
0.78
45
0.88
50
0.98
The DFOV determines the anatomic area imaged by a single reconstruction.
•
->Area equals π r2 (Area =3.14 x radius x radius)
•
->The 50 cm FOV has a 25 cm radius, so its area equals 1963 cm2.
•
->The ROI or magnification factor determines the anatomic area covered by a
magnified image.
Example: A CRT pixel represents 0.5 by 0.5mm. Magnify pixel size by 2. Each CRT pixel now
represents 0.25 by 0.25mm of anatomy.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
11-33
LightSpeed ™ 4.X
Pixel Size equals DFOV
P Matrix size
2.00
1.75
Pixel area
equals
pixel size
squared
1.50
1.25
pixel size
(width)
in mm
1.00
0.75
512
Matrix
0.50
0.25
0.00
0
50 100 150 200 250 300 350 400 450
DFOV in mm
Pixels and CT Numbers
Besides anatomic location and area, each CT pixel also represents a CT number, which in
turn indicates tissue density.
•
An ROI averages the values of the enclosed pixels, and displays the resulting Mean
value.
•
Standard Deviation describes the difference between the minimum and maximum ROI
value.
•
A large ROI provides a larger, more accurate statistical sample than a small ROI.
An image pixel represents a three dimensional volume, or voxel. It represents anatomy
with a location, an area, and a pixel (density) value. The system flattens the 1.25, 2.5, 3.75, 5,
7.5, 10mm scan thickness into a two dimensional screen image. If a pixel represents a
variety of tissues, the system averages the contents to produce an averaged, rather than
accurate, pixel value. Uniform tissues (within the voxel) produce fairly accurate pixel values.
CT pixel shading shows relative density. Denser materials weaken X-Ray and produce
whiter pixels. (Assumes Inverse Video OFF)
MR pixel shading reflects relative physiology. Whiter pixels represent molecules that
relaxed earlier after magnetic alignment than the darker areas.
Reformat displays non axial planes created from contiguous pixels extracted from
multiple images. 3D locates similar pixel values within contiguous images, and generates a
mathematical model to produce images that appear three dimensional. BMD samples pixel
values to estimate bone or tissue density.
11-34
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
General Information
Reconstruction assigns one value to every image pixel. CT uses pixel values of -1024 to
+3071. MR uses pixel values of ±16,000. The screen pixel translates the assigned value into
one of the 256 shades of gray. Vary the gray scale window width and level to select
anatomy for display. Window Width determines the quantity of gray pixel values. Window
Level selects the center Window Width pixel value.
Example: Two windows may contain identical widths of 100 values, but display completely
different anatomy, because one has a level of -100 and the other has a level of 150
Window Width
The system uses 256 CRT gray shades to display 4000 CT pixel values. The Window Width
selection determines the number of CT values represented by each CRT shade of gray. A
narrow window assigns fewer pixels to each gray level than a wide window.
Example: WW = 256 System assigns one pixel value to each gray shade WW = 2560 System
assigns ten pixel values to each gray shade
Enlarge the window to display anatomy that includes air, tissue, and bone, and subtle
differences in the tissue vanish, because the system assigns too many pixel values to each
shade of gray.
Narrow the window, then adjust the level to display only soft tissue. Subtle differences in
tissue density appear, because the system assigns fewer pixel values to each shade of gray.
Adjust the window whenever the display anatomy changes. Large window widths display a
range of anatomic structures and densities, while narrow windows enable subtle density
discrimination within the anatomy of interest.
Window Level
The Level equals the CT number value of pixel in the center of the Window Width range. The
Level value receives the middle shade of gray. The system displays pixel values that fall
between the center and upper window level as gray to off white. It displays pixel values that
fall between the center and lower window values as gray to charcoal. When you change the
level, the window width moves up and down the CT number line. The CT values change with
Window Level, but the Window Width and number of pixels per gray level don’t change.
Inverse Video reverses display conventions. Dense or high numbers are portrayed as black
rather than white.
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© 2005 General Electric Company. All rights reserved.
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LightSpeed ™ 4.X
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2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
QUALITY ASSURANCE
Chapter 12
QUALITY ASSURANCE
In order to assure consistent image quality over the system's lifetime, establish and
maintain a regular Quality Assurance (QA) program.
Scan a known material (usually a phantom) under a prescribed set of conditions.
•
Compare the results to previous or optimum values.
•
Repeat these tests on a regular basis to detect changes in image quality values before
the problem becomes visible.
– If you notice a degradation in image quality, or a change in QA values, you can
schedule a site visit and let the service person or imaging physicist run more detailed
tests.
– Early intervention could prevent a major breakdown.
Quality Assurance begins with baseline performance data acquired during system
installation, or after the repair or replacement of an X-Ray tube, collimator, detector, DAS, or
PDU circuitry.
•
Compare subsequent QA results against the baseline.
•
You can save baseline images for a visual comparison with your daily QA checks, but
the measurement values provide a more objective way to monitor quality.
NOTE: Copy the QA Data Form found at the end of this section. Use the form to record
baseline data and subsequent QA data.
QA Phantom
Use the Quality Assurance Phantom to assess system performance and establish an
ongoing Quality Assurance program.
The phantom design provides maximum performance information with minimum effort.
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12-1
LightSpeed ™ 4.X
This phantom measures six aspects of image quality.
•
Contrast Scale
•
High Contrast Spatial Resolution
•
Low Contrast Detectability
•
Noise and Uniformity
•
Slice Thickness
•
Laser Light Accuracy
The QA phantom contains three sections, each corresponding to a single scan plane.
•
Section 1: Resolution block S0mm scan location
•
Section 2: Contrast membrane S40mm scan location
•
Section 3: Water bath S60mm scan location
The following illustration contains a list of the sections and corresponding tests.
12-2
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
QUALITY ASSURANCE
Figure 12-1 QA Phantom
Section 1
High contrast resolution
Contrast scale
Slice thickness
Laser accuracy
Location: S0mm
Section 2
Low contrast detectability
Location: S40mm
Section 3
Noise and Uniformity
Location: S60mm
QA Schedule
Each facility determines QA and phantom calibration schedule.
GE recommends that you acquire scans of Sections 1, 2 and 3 of the QA Phantom each day.
Create a Scan Protocol file for these QA scans.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
12-3
LightSpeed ™ 4.X
Figure 12-2 QA Phantom Alignment
Vertical Reference Line
Circumferential
Reference Line
Horizontal
Reference Line
Horizontal
Reference Line
Note:
Reference lines are etched
into the plastic and are
unpainted.
System Performance
Maintain Image Quality
Many factors affect Image Quality:
•
Proper alignment of X-Ray tube, DAS, detector, and table
•
KV and mA adjustments within specifications
•
Current Calibration files
•
Tube Warmup every time the system recommends it
•
Daily Fastcals
•
Appropriate pixel size, slice thickness, reconstruction algorithm, and special processing
selections during Scan Rx
•
Patient remains motionless during scan acquisition
At least three people must cooperate to produce optimum images:
•
Service representative aligns the system and adjusts kV and mA
•
Operator follows facility guidelines to maintain daily image quality, prescribe the
exams, and update the calibration files
•
Patient follows operator (and autovoice) instructions during exam
A QA program helps locate the source of image quality problems:
12-4
•
Replaces patient with phantom
•
Provides standard Scan Rx parameters
•
Provides System Performance tests and comparisons
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QUALITY ASSURANCE
Position the QA Phantom
Place the QA phantom on the phantom holder, and level it.
Turn the knob facing the cradle CW to tilt the top of the phantom AWAY from the gantry.
Use the laser alignment lights to position the phantom:
1. Align the axial light to the circumferential line marking Section 1.
2. Align the coronal light to the horizontal lines on either side of the phantom.
3. Align the sagittal light (where it strikes the top of the phantom) to the vertical line on the
top of the phantom.
4. Position the phantom and select
.
Prescribe the QA Series for the Resolution, Low Contrastability, and Noise and
Uniformity Tests
1. Click [New Patient] to display the Patient/Exam Parameters screen.
Š Use the same ID for all related QA tests so you can store the exams together.
2. Enter any additional information in the corresponding data field(s). (Optional)
3. Exam Description: Enter up to 22 characters to describe the test. (Recommended)
4. Select a protocol from the anatomical selector to select a QA protocol. (If available)
If your facility hasn't created a QA protocol, use the following parameters to finish the QA
series prescription:
On the Helical View Edit screen select the following parameters:
Table 12-1 Parameters for QA
Interface
Input
Entry
Head First
Position
Supine
Anatomical Reference
QA
Landmark Location
0 on resolution phantom at circumferential line/cross hatch.
Scan Type
Helical 0.625:1
Scan Range
I0 - S60
Thickness
10
Table Speed
6.25
Recon Interval
10
Tilt
0 degrees
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Interface
Input
Scan FOV
Small
kV
120
mA
160
Rotation Speed
1 second
DFOV
25cm (phantom diameter:approximately 21.5cm)
Algorithm
Standard and Bone to test high contrast resolution.
Standard to test low contrast detectability
Standard for pixel value noise and uniformity
Matrix
512
Contrast
None
Special Processing
None
Analyze the QA Images
1. Display the first QA image, which is section #1 at scan location S0.
2. Copy the QA Data Form at the end of this section.
3. Record the data from the tests that follow in the corresponding area of the form.
4. Compare the current values to previously recorded values.
Š If you notice a significant change in values, check the Small SFOV calibration status.
5. Calibrate the Small SFOV if the most recent calibration date falls outside the guidelines
established by your facility.
6. Report significant changes, or values that fall outside suggested windows, to your
supervisor or imaging physicist.
7. Follow facility procedures to notify service personnel.
8. Perform the following:
a) Contrast Scale test at scan location S0 of the helical scan.
b) High Contrast Spatial Resolution test at scan location S0 of the helical scan.
c) Low Contrast Detectability test at scan location S40 of the helical scan.
d) Noise and Uniformity test at scan location S60 of the helical scan.
e) Slice Thickness test at scan location S0 of the axial slice thickness scans.
f) Alignment Light Accuracy test at scan location S0 of the Alignment Light test scan.
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QUALITY ASSURANCE
Contrast Scale
Section 1 of the Phantom Tests the Contrast Scale
CT assigns CT numbers, also called (HU) Hounsfield Units, to the attenuation values of X-Ray
passing through a variety of material densities.
Software makes the attenuation visible by assigning shades of gray to groups of numbers
selected with the Window Width/ Level functions during image Display.
For test purposes, the CT values of water and plexiglass in the phantom represent the
standard against which you track the system contrast scale over time.
The test for contrast scale follows:
Figure 12-3 Contrast Scale Phantom Section
Position 10mm box ROI
over water
Position 10mm box ROI
over Plexiglass
1. Select Box ROI to position a 10mm box cursor on the image, as shown in Table 12-3 on
page 7.
2. For consistency, use the same size cursor and location each time you perform this test.
3. Select Grid to provide a reference.
4. Select Box ROI to position a cursor over the Plexiglass resolution block (refer to
Table 12-3 on page 7).
5. Record the mean CT number on the QA Data Form.
6. Optional: Record the Standard deviation
7. Select Box ROI to position a cursor over water (refer to Table 12-3 on page 7).
8. Record the mean CT number for water on the QA Data form.
9. Optional: Record the Standard deviation
10. Subtract the CT number of water from the CT number of Plexiglass
Š Record the difference on the QA Data form.
Š The difference should equal 120 +/-12.
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High Contrast Spatial Resolution
Section 1 (Figure 12-4) of the phantom contains six sets of bar patterns in a Plexiglass block
used to test high contrast spatial resolution.
Each pattern consists of sets of equally sized bars and spaces
Water fills the spaces and provides about 12% (120 HU) contrast.
The resolution block contains the following bar sizes:1.6mm, 1.3mm, 1.0mm, 0.8mm, 0.6mm,
and 0.5mm.
1. Examine the bar patterns to determine the limiting resolution, defined as the smallest
bar pattern in which you see all five bars.
2. You should see all five 0.6mm bars in images reconstructed with the Bone algorithm
(15cm FOV).
3. Using the standard algorithm, measure the standard deviation of the pixel values in a
single or multiple bar pattern to provide a quantitative method for assessing changes in
system resolution.
4. ROI standard deviation provides a good indicator of system resolution and a sensitive
method to detect changes in system resolution.
The recommended procedure follows:
Figure 12-4 High Contrast Spatial Resolution Section
Position box cursor over largest
bar pattern, and size it until it
fits over the pattern.
Optional: repeat for 1.3mm,
1.0mm and 0.8mm patterns
5. Select Erase to remove previous ROI data.
6. Position a box cursor over the largest (1.6mm) bar pattern, and size it to fit within the bar
pattern as shown in Figure 12-4.
7. Record the standard deviation on the QA data form.
Š Standard deviation should equal 37 +/- 4, if you used standard algorithm.
Optional: Repeat this procedure for the 1.3, 1.0, and 0.8mm bar patterns.
8. Record the standard deviation on the QA data form.
12-8
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QUALITY ASSURANCE
MTF (optional)
The Modulation Transfer Function (MTF) mathematically quantifies high contrast
resolution.
MTF measures the contrast preserved for a sine wave pattern as a function of frequency.
An MTF curve begins at 1 for zero frequency, and decreases as frequency increases.
Example: An MTF of 1 equals total preservation of contrast
Example: An MTF of 0.5 equals 50% loss of contrast
The limiting resolution equals the frequency at which MTF falls to 0.
An MTF curve is shown in Figure 12-19.
Measure Frequency in line pairs per centimeter.
One line pair per centimeter equals one 5mm Plexiglass bar next to one water filled 5mm
space.
Optional: Consult the publication listed as Reference 1 in section for MTF measurement
instructions (Droege RT, Morin RL. “A Practical Method to Measure the MTF of CT Scanners,”
Medical Physics, Volume 9, No. 5, pp 758-760, 1982).
Low Contrast Detectability
Section 2 of the QA phantom tests low contrast detectability, defined here as the smallest
hole size visible for a given contrast level at a given dose.
This phantom section contains a doped polystyrene membrane suspended in water and
pierced by a series of holes in the following sizes: 10.0mm, 7.5mm, 5.0mm, 3.0mm, and
1.0mm.
•
The difference in CT numbers between the water, and water plus plastic, equals the
contrast in Hounsfield Units (HU).
•
Your first contrast measurement of the QA phantom establishes its baseline.
Subsequent measurements should fall within 0.1% of the baseline. (1HU)
•
Divide the HU value by ten to obtain the contrast in percent.
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•
Measure the contrast between the plastic membrane and the surrounding water in the
following manner:
Figure 12-5 Low Contract Detectability Section
A. Position box ROI over polystyrene
membrane above holes.
B. Position box ROI over
water above membrane.
Subtract B from A.
Subtract D from C.
Count visible holes.
D. Position box ROI
over water below
membrane.
C. Position box ROI over polystyrene
membrane below holes.
1. Display an image of Section 2, which is at scan location S40.
2. Select Erase to remove previous ROI data.
3. Select a Box ROI, and adjust the size to a rectangle about 5mm high and 50mm long.
4. First, position the ROI over the polystyrene membrane, just above the holes, as shown in
Figure 12-5.
5. Record this membrane CT number in the Top CT# column.
Š QA data form (Figure 12-11) at the end of this section.
6. Select Box ROI to position a cursor over the (100%) water section above the membrane,
as shown in Figure 12-5.
7. Record this water CT number in the Top CT# column.
8. Subtract the water's CT number from the membrane's CT number.
9. Record the difference.
10. Select Erase to remove previous ROI data.
11. Select Box ROI to position the cursor over the polystyrene membrane, just below the
holes, as shown in Table 12-5, “Low Contract Detectability Section,” on page 10-C.
12. Record this membrane CT number in the Bottom CT# column.
Š QA data form (Figure 12-11) is at the end of this section.
13. Select Box ROI to position the cursor over the (100%) water section below the
membrane, as shown in Figure 12-5.
14. Record this Water CT number in the Bottom CT# column.
15. Subtract the water's CT number from the membrane's CT number.
12-10
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QUALITY ASSURANCE
16. Record the difference.
17. Select Erase to remove previous ROI data.
18. Adjust the Window Width to 30 and the Window Level to the CT number you recorded
for water.
19. Count and record the number of visible holes.
Noise and Uniformity
Section 3 (Figure 12-6) of the phantom tests noise and uniformity, which is at scan location
S60.
Noise limits low contrast resolution, and masks anatomy with similar structure to
surrounding tissue.
QA phantom Section 3 provides a uniform image by which to assess image CT number noise
and uniformity.
Use the Standard algorithm to reconstruct the image.
Figure 12-6 Noise and Uniformity Section
Position 2cm box ROI over
the center of the image.
Optional: Take a box ROI
at the 12 o’clock position
75mm from center box.
Optional: Take a box ROI at
the 3 o’clock position
75mm from center box.
Image noise equals the standard deviation of CT numbers within a region of interest (ROI).
Noise results from electronic, mechanical, and mathematical differences in detected X-Ray
energy, electronic outputs, and reconstruction algorithms.
Tube Warmups, up to date calibration files, and daily Fastcals minimize noise and help
provide uniform images.
Refer to Figure 12-6.
1. Select Erase to remove previous ROI data.
2. Select Box ROI to position a 2 cm box ROI over the center of the image.
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3. Record the mean CT number and standard deviation on the QA Data Form.
Š QA data form (Figure 12-11) is at end of this section.
4. Optional: Select Box ROI and move the cursor to the 12 o'clock position.
5. Record the mean CT number and standard deviation on the QA Data Form.
6. Optional: Select Box ROI to move the cursor to the 3 o'clock position.
7. Record the mean CT number and standard deviation on the QA Data Form.
Š If the Image is reconstructed with Standard algorithm and Small SFOV, the Mean of
Center ROI should equal 0+/-3.
Š Standard deviation of the center ROI should equal 3.0 +/- 0.4
Š The uniformity difference between the center ROI and the average of the edge ROIs
should be 0 +/- 3.
Slice Thickness
Section 1 of the phantom also tests slice thickness.
Both sides of the resolution block contain a pattern of air filled holes designed to
demonstrate slice thickness (refer to Figure 12-7).
Figure 12-7 Slice Thickness Section
Air filled
holes
The resolution block contains holes drilled 1mm apart and positioned to form a line at 45
degrees to the scan plane.
Each visible hole in the image represents 1mm of beam thickness.
The software assigns less negative CT numbers to partial hole images or holes located on
the edge of the slice profile.
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QUALITY ASSURANCE
Prescribe the QA Series for the Slice Thickness Test - Phantom Section #1
1. Select a protocol from the anatomical selector to select a QA protocol (if available).
2. If your facility hasn't created a QA protocol, use the following parameters to finish the
QA series prescription:
3. On the Axial View Edit screen select the following parameters:
Table 12-2 QA Protocol for Slice Thickness
Interface
Input
Entry
Head First
Position
Supine
Anatomical Reference
QA
Landmark Location
0 on resolution phantom at circumferential line/cross hatch.
Scan Type
Axial
Prescribe 4 Groups
Scan Range
Group
Thickness
Scan Range
Spacing
1
5mm/4I
I7.5 - S7.5
0
2
3.75mm/4I
I5.6 - S5.5
0
3
2.5mm/8I
I8.75 - S8.75
0
4
1.25mm/8I
I4.4 - S4.4
0
5
0.625mm/16I
I4.6875 - S4.6875
0
6
2.5mm/4I
I3.75-S3.75
0
Tilt
0 degrees
Scan FOV
Small
kV
120
mA
260
Rotation Speed
1 second
DFOV
25cm (phantom diameter:approximately 21.5cm)
Algorithm
Standard
Matrix
512
Contrast
None
Special Processing
None
4. Analyze the Slice Thickness in Images
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5. To determine slice thickness, display the image at the recommended window level and
width, and count the visible holes.
Š Black lines in the image represent a full millimeter of slice thickness.
Š Gray lines count as fractions of a millimeter; two equally gray holes count as a single
1mm slice thickness.
Š Refer to Figure 12-8.
Recommended window width: 250
Recommended window level:
•
-100 for 1.25mm
•
-25 for 2.5mm
•
+25 for 3.75mm
•
+ 50 for 5.0mm
Figure 12-8 Slice Thickness Lines
Adjust the window width and level, then
count the lines, which represent the air
filled holes.
Note: The slice thickness bars
are less distinctive in helical scans..
Each black line represents one
millimeter of slice thickness. Gray
lines represent fractions of a
millimeter
You should see one line for each millimeter of scan thickness.
Figure 12-8 represents a 5mm image.
Alignment Light Accuracy (Crucial During Biopsies)
The manufacturers drilled deeper center holes on the reference to help identify them in the
image.
The center hole position corresponds precisely to the etched marker placed on the
circumference of the phantom.
When you use an accurate light, and align the phantom's circumferential etched marker to
the axial light, the resulting image should contain a symmetrical hole pattern around the
center (longer) hole in the slice thickness pattern.
Refer to Figure 12-9.
For best results, use the 2mm/4i slice thickness.
12-14
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QUALITY ASSURANCE
Prescribe the QA Series for Alignment Light Accuracy - Phantom Section #1
Select a protocol from the anatomical selector to select a QA protocol. (If available) If your
facility hasn't created a QA protocol, use the following parameters to finish the QA series
prescription:
On the Axial View Edit screen select the following parameters:
Table 12-3 Parameters for Alignment Lights Check
Interface
Input
Entry
Head First
Position
Supine
Anatomical Reference
Type EX for the external alignment light test
Type IN for the internal alignment light test.
Landmark Location
0 on resolution phantom at circumferential line/cross hatch.
Scan Type
Axial
Scan Range
I3.75 - S3.75
Thickness
2.5 mm/4i
Tilt
0 degrees
Scan FOV
Small
kV
120
mA
260
Rotation Speed
1 second
DFOV
25cm (phantom diameter:approximately 21.5cm)
Algorithm
Standard
Matrix
512
Contrast
None
Special Processing
None
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Figure 12-9 Alignment Light Section
Center hole position corresponds to
etched line around phantom
circumference.
Align etched line on phantom
to positioning light
1. Align the phantom to the Internal light and scan it.
Š The actual scan plane should equal 0 +/- 2.0mm.
2. Align the phantom to the External light and scan it.
Š The actual scan plane should equal 0 +/- 2.0mm.
Figure 12-9 and phantom positioning instructions.
3. Align the vertical, horizontal and circumferential lines on the phantom to the
corresponding laser lines.
Š Azimuth 0 laser: Center phantom left and right within the FOV
Š Azimuth 90 and 270 lasers: Center phantom up and down within the FOV.
4. Scan the phantom.
5. Display the resulting phantom image.
Š Refer to Figure 12-9.
6. Select Grid to check sagittal and coronal light accuracy.
Š Refer to Figure 12-10.
7. Center the phantom to isocenter, +/-4.0mm, along the sagittal and coronal planes.
Š Refer to Figure 12-9.
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QUALITY ASSURANCE
Figure 12-10 Grid Check
A125.0
Ex: 100 Console1
Ser: 1
QA S0.0
Img: 2
Hospital name a centered
Patient name 5mm scan
Patient ID
date of scan
matrix size
mag factor
DFOV 25.0cm
STND
L
1
2
5
.
0
R
1
2
.5
0
kV 120
mA 260
Small
5.0mm
Tilt 0.0
P125.0
S0.0
R0.0
W = 250 L = –50
QA phantom “Prone” or “Supine”
A0.0
Typical Results and Allowable Variations
Because the human eye determines clinical image quality, it remains subjective and difficult
to define.
GE expects the standards of allowable variation in image quality parameters to vary with
the installation and image evaluator(s).
GE encourages you to establish and follow a Quality Assurance (QA) program so you can
discover any degradation of image quality before it effects clinical images.
Over time, institutions use the QA procedure to establish a correlation between acceptable
clinical image quality and acceptable variations in the image performance indices included
in the program.
Compare your images to the set of performance images that accompanied your system.
This section contains suggested allowable variations; don't mistake them for absolutes.
Compare any parameter variation to the maximum deviation specified in the next section
called, Dose and Performance.
Make sure you used the prescribed technique, then follow your facility guidelines to inform
service when the variations reach the specified maximum deviation.
Contrast Scale
The difference in CT numbers between the Plexiglass resolution block and water should
equal 120, with a suggested allowable variation of 10%.
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High Contrast Spatial Resolution
The standard deviation for an ROI in the 1.6mm bar pattern should equal 37 +/- 4 for the
standard algorithm.
Axial Scan Slice Thickness
Slice thickness should not vary by more than +/- 1mm from the expected value, when
evaluated according to instructions.
Relatively large tolerance due to size of markers in phantom.
Low Contrast Detectability
Because this test relies upon the perceptual judgment of the person counting visible and
well-defined holes, GE can't suggest an allowable variation. Rather, we suggest you choose
a single, barely visible hole and closely monitor that particular hole during subsequent
testing for degradation in this image parameter.
Noise & CT Number of Water
When you correctly image and analyze the water section of the phantom, you should see a
CT number for water of 0 +/- 3 HU for the center ROI. The uniformity difference between the
Center ROI and the average of the edge ROIs should be 0 +/- 3 for Small Body (0 +/- 10
maximum deviation if Large Body is used).
Expect the noise in the center of the image to approximately equal 3.0 +/- 0.4.
References
Droege RT, Morin RL. “A Practical Method to Measure the MTF of CT Scanners,” Medical Physics, Volume 9, No. 5,
pp 758-760, 1982.
Jacobson DR. “Quality Assurance for Computed Tomography — Correlation with System Performance,”
Application of Optical Instrumentation in Medicine XI, D. Fullerton, Editor, Proc. SPIE 419, pp 157-165, 1983.
AAPM, “Phantoms for Performance Evaluation and Quality Assurance of CT Scanners,” Report No. 1, American
Association of Physicists in Medicine, 1977
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QUALITY ASSURANCE
Figure 12-11 .QA Master Data Form
QA Data Form
Contrast Scale
date:
Mean CT
#
Std. Dev.
plastic
High Contrast
Bar Size
Spatial Resolution
spec
37+/–4
Std. Dev.
1.6
1.3
1.0
water
0.8
difference
120+/–12
# of Visible Lines
Slice Thickness
5.0
W/L 100/+25
2.5
90/270 laser
1.25
W/L 100/–25
centered Y/N
EXT axial
3.75
W/L 100/50
Low Contrast
detectability
Alignment Light
Accuracy
INT axial
0 laser
W/L 100/–100
Top
CT #
Bottom
CT #
membrane
water
difference
smallest hole
W/L used (30/0)
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© 2005 General Electric Company. All rights reserved.
Noise and Uniformity
spec:
Mean CT #
(Ctr. ROI)
0 +/– 3
Std. Dev.
(Ctr. ROI)
3.2+/– 0.3
Uniformity
(Ctr. MeanEdge Mean)
measurement:
0 +/– 3
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DOSIMETRY
Dosimetry information is provided in terms of the CTDI and CTDIw dose indices. Optionally
CTDIvol and its associated DLP (dose length product) is automatically computed and
displayed on the patient Rx menu to assist in managing patient dose. This section provides a
brief description to help you better understand these dose reporting standards.
General Information
Dose is the amount of energy imparted by the X-ray beam at a given point in an exposed
material (patient tissue, phantom, air, etc. ) and is measured in units of mGy (milli Gray).
(The old unit was the Rad which equals 10 mGy.) Dose is dependent on the energy
absorption factors of the material and on the X-ray exposure. The X-ray exposure is
measured in C/kg (coulombs per kilogram) and is dependent on the technique factors used
for the scan. The dose is generally proportional to the exposure which increases with
increasing mA, kV and scan time. The X-ray exposure to a point occurs from both direct
X-ray from the tube and from scattered X-ray due to adjacent material exposure.
NOTE: CTDIvol = CTDIw/Scan mode adjustment factor
Reference IEC 60601-2-44.
See Scan mode adjustment factor table for factor to use.
Patient biological risk is related to dose but is also highly dependent on the specific organs
exposed. The effective dose is a way to characterize patient risk. The effective dose is the
sum of the doses weighted in accordance with the specific radio-sensitivity of the particular
organs or tissues exposed. Weighting values are published in ICRP 60 (International
Committee on Radiation Protection, Publication 60). Although we can accurately describe
the X-ray exposure potential to a patient for a CT scan, we can not easily determine the
patient dose or risk in terms of effective dose. This is because each patient is anatomically
unique and the specific details of his or her anatomy along with the source exposure must
be processed using time consuming monte-carlo computer programs to predict how
radiation will be scattered and accumulated at various points within the patient.
Since it is not possible to characterize the specific dose given to individual patients, the
CTDI and CTDIw dose indices are provided to help make relative comparisons. These dose
index values can be used to compare CT systems and to help you select operating
conditions for scanning.
Figure 12-12 CTDI Dose Reference Phantom Description
B
E
A
D
12-20
C
Head Phantom
Body Phantom
Material
Thickness
A thru E
A
B thru E
16 cm dia.
32 cm dia.
PMMA (polymethyl methacrylate)
>14 cm thick
Pencil chamber openings
Center
Peripheral 1 cm from surface
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QUALITY ASSURANCE
CTDI
CT Dose Index (CTDI) was established by the FDA and has been in use for many years. The
method is defined by U.S. Federal Regulation 21CFR 1020.33 (C). It provides a way to
determine the dose at specific points (center and peripheral) in a head or body size
reference phantom (refer to Figure 12-12). The CTDI dose is the dose absorbed in the
phantom material (PMMA) at a point when a volume of 7 contiguous slices are scanned
adjacent to each side of the point. (The contiguous adjacent slices contribute to much of the
total dose.)
Mathematical Definition of CTDI
7
&7',
1
Q7
Q = number detector macro rows per scan
7 = row detection width
D(z) = Z axis dose profile (absorbed in PMMA)
' ]G]
7
CTDI dose tables and index factors are provided in the following section. To determine the
CTDI dose, select the appropriate standard technique dose (head or body) and multiply by
the factors for describing the technique used.
Figure 12-13 CTDI TABLES and FACTORS
Typical Techniques for CTDI, CTDI100, and CTDIw
HEAD-axial-cine
BODY-axial-cine
25cm SFOV
50cm SFOV
120kv
120kv
260 mA
260 mA
1 sec scan
1 sec scan
16x1.25
10mm, 2i mode
Figure 12-14 CTDI Dose Values
TABLE of CTDI DOSE VALUES (mGy)
AT TYPICAL TECHNIQUE
Head A
Head B
Body A
Body B
44.17
43.62
14.17
26.10
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Figure 12-15 CTDI KV, Scan Mode, and mAs Adjustment Factors
KV Adjustment Factor
KV
Head A
Head B
Body A
Body B
80
0.34
0.37
0.27
0.33
100
0.63
0.65
0.57
0.61
120
1
1
1
1
140
1.37
1.36
1.44
1.36
mAs ADJUSTMENT FACTOR = Rx mA * Rx single rotation time in seconds/ 260
Scan Mode Adjustment Factor
16 Slice Scan Modes
Pitch
Factor
8 Slice Scan Modes
0.5625:1
0.9375:1
1.375:1
1.75:1
0.625:1
0.875:1
1.35:1
1.675:1
1.78
1.07
0.73
0.57
1.60
1.14
0.74
0.60
In the cases of cardiac helical scans, the following Scan Mode adjustment factor should be
used:
Figure 12-16 Cardiac Scan Mode Adjustment Factors
12-22
Helical Pitch Factor
GE Traditional Def.
Helical Pitch Factor
(IEC Definition)
Cardiac Helical Scan
Mode Factor
4.4
0.275
3.64
4.8
0.30
3.33
5.2
0.325
3.08
5.6
0.35
2.86
6.0
0.375
2.67
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© 2005 General Electric Company. All rights reserved.
QUALITY ASSURANCE
Table 12-4 Table of Acquisition Mode Parameters for CTDI, CTDI100, and CTDIw
Table of Acquisition Mode Parameters for CTDI, CTDI100, and CTDIw
Acq.
16 x 1.25
16 x 0.625
8 x 2.50
8 x 1.25
4 x 3.75
4 x 2.50
4 x 1.25
4 x 0.625
2 x 0.625
.5625
11.25
5.625
—
—
—
—
—
—
—
.625
—
—
12.5
6.25
—
—
—
—
—
Helical mm/Rotation per Pitch
and Acquisition Mode
(mm)
.875
.9375
1.35
1.375
—
18.75
—
27.5
—
9.375
—
13.75
17.5
—
27.0
—
8.75
—
13.5
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
1.675
—
—
33.5
16.75
—
—
—
—
—
1.75
35.0
17.50
—
—
—
—
—
—
—
16i
1.25
.625
—
—
—
—
—
—
—
Axial and Cine
Slice Thickness
(mm)
8i
4i
2i
2.5
5.0
10.0
1.25 2.5
5.0
2.5
5.0
10.0
1.25 2.5
5.0
—
3.75 7.5
—
—
—
—
—
—
—
—
—
—
—
.625
Step
and
Shoot
1i
—
10.0
—
10.0
—
—
—
—
1.25
3i
—
—
—
—
7.5
5.0
2.5
1.25
—
Table 12-5 CTDI Aperture Adjustment Factors for Large Spot
CTDI Aperture Adjustment Factors for Large Spot
Acquisition Mode
Head A
Head B
Body A
Body B
16 x 1.25
1.00
1.00
1.00
1.00
16 x 0.63
1.23
1.25
1.24
1.24
8 x 2.50
1.01
1.00
1.00
1.03
8 x 1.25
1.25
1.27
1.25
1.25
4 x 3.75 & 7.5mm
step/shoot
1.06
1.08
1.06
1.06
4 x 2.50 5mm step/shoot
1.25
1.26
1.25
1.30
4 x 1.25 2.5mm step/shoot
1.53
1.54
1.54
1.57
4 x 0.625 1.25mm
step/shoot
1.10
1.12
1.10
1.15
2 x 0.625 thin twin & single
slice
0.96
2.60
0.90
2.60
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
12-23
LightSpeed ™ 4.X
Table 12-6 Table of Acquisition Mode Parameters for CTDI, CTDI100, and CTDIw
CTDI Aperture Adjustment Factors for Small Spot
Acquisition Mode
Head A
Head B
Body A
Body B
16 x 1.25
1.01
1.01
1.01
1.01
16 x 0.625
1.12
1.14
1.12
1.13
8 x 2.50
0.96
0.96
0.97
0.96
8 x 1.25
1.15
1.17
1.15
1.15
4 x 3.75 & 7.5mm
step/shoot
1.05
1.07
1.05
1.05
4 x 2.50 5mm step/shoot
1.15
1.16
1.15
1.19
4 x 1.25 2.5mm step/shoot
1.41
1.43
1.46
1.49
4 x 0.625 1.25mm
step/shoot
0.92
0.94
1.10
0.97
2 x 0.625 thin twin & single
slice
0.46
1.26
0.42
1.28
For example, the peripheral CTDI body dose for a 12.5 mm/rot Helical scan in 0.625:1 mode,
scan at 150 mA, 0.8 Sec per rotation and 140 kv is determined as follows:
26.10 mGy
body peripheral dose at typical technique from CTDI table
x 1.36
140 kv factor from CTDI kv table
x 1.6
0.625:1 adjustment factor from CTDI Scan Mode table
x 0.96
12.5 mm/rot aperture adjustment factor from:
CTDI aperture factor < 24 KW table
(i.e. 140 kv x 150 mA =18 KW which is < 24 WK)
x 120/260
120 mAs adjustment factor (150mA x .8Sec)
=25.16 mGy
computed CTDI Body Peripheral dose
CTDIw
CTDIw is a new dose index defined in international standard IEC 60601-2-44. CTDIw is a
single number which consists of 2/3 of the CTDI100 peripheral dose plus 1/3 of the CTDI100
central dose. The CTDI100 dose is similar to CTDI since it is measured using the same PMMA
phantom center and peripheral points; however, the 14 contiguous slices are changed to a
fixed 100mm. Also, although dose is measured at locations within the PMMA phantom, it is
quoted as the dose absorbed in air rather than PMMA (absorption in air is about 11% higher
than absorption in PMMA).
12-24
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
QUALITY ASSURANCE
CTDI100 provides a better relative index for narrow slices than CTDI. CTDI can give the
impression that narrow slices produce less dose than thicker slices but this is only because
the index is defined for 14 slices and typical modern procedures will include scattered dose
form from more than 7 adjacent slices. Combining 2/3 of the CTDI100 peripheral dose with
1/3 of the CTDI100 central dose provides a single simple metric (CTDIw) to describe the
relative dose associated with a scan.
Mathematical Definition of CTDI100 and CTDI W
Q = number detector macro rows per scan
7 = row detection width
Da(z) = dose profile in Z axis (asborbed in air)
+50PP
&7',
1
=
Q7
100
' D]G]
–50PP
&7',
Z
=
[ &7',
SHULSKHU DO+
[ &7',
FHQW
CTDI100 and CTDIw dose tables and index factors are provided in the following section. The
system computes CTDIvol automatically. However you may compute either the CTDI100 or
CTDIw in a similar manner as for CTDI. Note that system computations may vary slightly
from manual calculations due to differences in round-off or truncation operations.
CTDI100 Typical Technique
(Typical techniques for CTDI100 and CTDIw are the same as for CTDI stated above)
Table of CTDI100 Dose Values (mGy) at Typical
Technique
Head A
46.41
Head B
48.59
Body A
14.09
Body B
29.07
TABLE of CTD I100 KV, SCAN MODE, and mAs
ADJUSTMENT FACTORS
(Refer to CTDI Table above)
Table 12-7 0 Aperture Adjustment Factors for Large Spot
CTDI100 Aperture Adjustment Factors for Large Spot
Acquisition Mode
Head A
Head B
Body A
Body B
16 x 1.25
1.00
1.00
1.00
1.00
16 x 0.625
1.24
1.24
1.25
1.24
8 x 2.50
1.01
1.00
1.00
1.03
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
12-25
LightSpeed ™ 4.X
CTDI100 Aperture Adjustment Factors for Large Spot (Continued)
Acquisition Mode
Head A
Head B
Body A
Body B
8 x 1.25
1.26
1.27
1.26
1.25
4 x 3.75 & 7.5mm step/shoot
1.08
1.08
1.08
1.09
4 x 2.50 5mm step/shoot
1.15
1.15
1.16
1.18
4 x 1.25 2.5mm step/shoot
1.53
1.54
1.54
1.57
4 x 0.625 1.25mm step/shoot
1.10
1.12
1.10
1.15
2 x 0.625 thin twin & single
slice
2.55
2.60
2.58
2.60
CTDI100 Aperture Adjustment Factors for Small Spot (<24kW)
Acquisition Mode
Head A
Head B
Body A
Body B
16 x 1.25
1.01
1.01
1.01
1.01
16 x 0.63
1.13
1.14
1.13
1.13
8 x 2.50
0.96
0.96
0.97
0.96
8 x 1.25
1.16
1.17
1.16
1.15
4 x 3.75 & 7.5mm step/shoot
1.08
1.08
1.08
1.09
4 x 2.50 5mm step/shoot
1.11
1.10
1.11
1.13
4 x 1.25 2.5mm step/shoot
1.41
1.43
1.46
1.49
4 x 0.625 1.25mm
step/shoot
0.92
0.94
1.10
0.97
2 x 0.625 thin twin & single
slice
1.22
1.26
1.22
1.28
Example 1 — The CTDI100 body peripheral dose for a 8.75mm/sec Helical scan in 0.875:1
mode, scan at 250 mA, 1.0 Sec per rotation and 120 kv is determined as follows:
12-26
29.07 mGy
body peripheral dose at typical technique from CTDI100 table
x 1.00
120 kv factor from CTDI kv table
x 1.14
0.875:1 adjustment factor from CTDI Scan Mode table
x 1.25
8.75 mm/rot 0.875:1 aperture adjustment factor from:
CTDI100 aperture factor large spot >24 KW table (i.e. 120 kv x 250 mA
=30 KW which is > 24 WK)
x 250/260
250 mAs (250 mA x 1 Sec) factor from CTDI table
= 39.83 mGy
computed CTDI100 Body peripheral dose
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
QUALITY ASSURANCE
Example 2 — The CTDI100 body center dose for example 1 is determined as follows:
14.09 mGy
body center dose at typical technique from CTDI100 table
x 1.00
120 kv factor from CTDI kv table
x 1.14
0.875:1 adjustment factor from CTDI Scan Mode table
x 1.26
8.75 mm/rot 0.875:1 aperture adjustment factor from:
CTDI100 aperture factor large spot >24 KW column (i.e. 120 kv x 250 mA
=30 KW which is > 24 WK)
x 250/260
250 mAs (250 mA x 1 Sec) factor
= 19.46 mGy
computed CTDI100 Body center dose
Example 3: The CTDIw body dose for example 1 and 2 is computed as:
39.83 x 2/3 + 19.46 x 1/3 = 33.04 mGy
Example 4: The CTDI body dose for a 10 mm 1i, 8 x 125 axial scan, at 150 mA, 1.0 Sec per
rotation, 120 kv and a 30 mm table increment is determined as follows:
14.09,
29.07 mGy
center, peripheral dose from CTDI100 table
x 1.00
120 kv factor from CTDI kv table
x 1/3
axial increment factor (10 x1)/30 from CTDI100 special case table
x 1.16, 1.15
8 x 125 aperture adjustment factor from:
CTDI100 aperture factor small spot < 24 KW column (i.e. 120 kv x 150
mA =18 KW which is < 24 WK)
x 150/260
150 mAs (150 mA x 1 Sec) factor
= 3.14,
6.43 mGy
CTDI100 center, peripheral dose
5.33 mGy
CTDIvol (3.14/3 + 6.43 x 2/3)
Example 5: The CTDI100 body center dose for a cardiac helical scan using 16 x 0.625 mm
slice thickness with helical pitch of 6.0, scan at 250 mA, 0.5 seconds per rotation, and 140 kv
is determined as follows:
14.09 mGy
Body center dose at typical technique from CTDI100 table
x 1.44
140 kv factor from CTDI kv table
x 2.67
Scan Mode adjustment factor from cardiac segment scan mode
adjustment table
x 1.25
Aperture adjustment factor for 16 x 0.625mm for large spot
x 0.48
250 mAs (250 * 0.5 / 260) factor from CTDI table
=32.50 mGy
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
12-27
LightSpeed ™ 4.X
Table 12-8 TABLE of CTDI100 Special Case Factors
TABLE of CTDI100 Special Case Factors:
axial increment factor
= (slice width) x (number of images per rotation)/(table
increment per rotation)
= (total exposure time/scan time per rotation) if table
increment is 0 (i.e axial, cine or fluoro)
This factor adjusts for non contiguous axial exposures. The
dose computation increases with overlapped exposures
and decreases with expo sure gaps.
clustered helical scan factor
= sum of individual cluster lengths/(x-ray on off distance)
where x-ray on off distance is the distance from the X-ray
on location of the first cluster to the X ray off location of the
last cluster.
sum of individual cluster length is (no of scans in cluster) x
(table speed) x (individual helical exposure time)
This is a confusing factor but it is required since the data collection length for a single helical
scan is longer then the total reconstructed image region. Hence multiple helical scans
contain overlapped exposure regions which increases the average CTDIvol per group. These
overlaps can be minimized by avoiding short duration helical scans whenever possible. That
is, it is better to perform a single long helical instead of a set of contiguous clustered helicals
if patient breath holding permits.
Other Dosimetry Information
DLP
The dose length product (DLP) for the CTDIw can also be automatically computed by the
system if desired and displayed on the Scan Rx menu. The DLP is given in mGyCm (milliGray
Centimeters). The DLP is computed and displayed for each group prior to the scan as well
as an accumulated DLP for all scans taken up to the current time during the exam. The final
exam accumulated DLP provides a convenient measure for maintaining patient or
procedure dose management statistics.
The DLP is computed given the CTDIw described above as follows:
axial scans:
DLP = CTDIw x (Number of images) x (Image thickness in cm)/(axial increment factor)
cine, fluoro, or 0 table increment axial scans:
DLP = CTDIw x (Image thickness in cm)
Helical scans:
DLP = CTDIw x (Exposure time) x (Table Speed)/ (clustered helical scan factor)
12-28
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
QUALITY ASSURANCE
Cardiac Helical Scans:
DLP = CTDIw x (Exposure time) x (Table speed)
= CDTIw x (Exposure time) x (Slice_Thickness x
pitch_factor / gantry_ period)
Dose Efficiency
The Dose efficiency is also automatically computed and displayed on the Scan Rx Menu.
The dose efficiency is a measure of how much of the Z-axis X-ray beam is used by the
system. Reference IEC 60601-2-44.
Scout Dose
The dose due to a scout is not reported since there are currently no standards to follow.
Generally, the scout dose will be a very small part of the total patient exam dose and
therefore would not have a practical significance.
Phantoms for Performance Testing
The results of this section conform to federal regulation 21CFR 1020.33 (c).
GE used the phantoms and procedures recommended in the CDRH final draft of “Routine
Compliance Testing for Computed Tomography X-Ray Systems” (dated April 26, 1984) to
measure dose and dose profile, and calculate CTDI.
GE used a 21.5cm water filled acrylic phantom to measure all Head performance tests.
Testers placed a 30cm wide acrylic ring around the water phantom to measure Body
performance.
Noise
Statistically measure the CT numbers represented by an array of pixels contained in a 2 x
2cm central region of interest (ROI)
Noise equals the standard deviation expressed in Hounsfield units, divided by 1000 to
represent the contrast scale between air and water, then multiplied by 100 to give a value in
percent.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
12-29
LightSpeed ™ 4.X
Noise
1020.33 (C) (3) i
The Standard Deviation In the Center scanned with Typical Technique and Standard 512
Recon at 5mm, 4i mode.
Head
Body
0.5%
1.3%
260 mAs
120 kVp
GE used the Small Body SFOV, rather than the Head SFOV.
Head: Use 25cm FOV
Body: Use 35cm FOV
Both SFOVs use similar resolution algorithms except the Small Body SFOV does not use the
bone/brain interface correction, which the phantom does not need.
The Small Body and Head SFOV produce negligible image performance differences.
Nominal Slice Thickness
1020.33 (C) (3) iii
Table 12-9 Nominal Slice Thickness
Head
Body
5.0mm, 4i mode
5.0mm, 4i mode
3.75mm, 4i mode
3.75mm, 4i mode
2.5mm, 4i mode
2.5mm, 4i mode
1.25mm, 4i mode
1.25mm, 4i mode
1.25mm, 1i mode
1.25mm, 1i mode
.625mm, 2i mode
.625mm, 2i mode
2.5mm, 8i mode
2.5mm, 8i mode
1.25mm, 8i mode
1.25mm, 8i mode
1.25mm, 16i mode
1.25mm, 16i mode
0.625mm, 16i mode
0.625mm, 16i mode
Sensitivity Profile
1020.33 (C) (3) iv
The sensitivity profile is a graph of the slice thickness. To recreate the original graphs, scan a
0.5mm tungsten wire in air that makes a 26.6° angle with scan plane. The wire is centered at
ISO center.
Refer to profile graphs in Figure 12-17 and Figure 12-18.
12-30
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
QUALITY ASSURANCE
Figure 12-17 Profile Curve
5.0mm, 4i mode & 2.5mm, 8i mode
Head
1.0
Relative Dose
0.8
0.6
0.4
0.2
0.0
–60
–50
–40
–30
–20 –10
0
10
20
Distance from Scan Center (mm)
30
50
60
Slice Sensitivity
Dose
2.5mm, 4i mode & 1.25mm, 8i mode
Head
1.0
40
Relative Dose
0.8
0.6
0.4
0.2
0.0
–60
–50
–40
–30
–20
–10
0
10
20
30
40
50
60
Distance from Scan Center (mm)
Slice Sensitivity
Dose
1.25 mm, 4i mode
Head
1.0
Relative Dose
0.8
0.6
0.4
0.2
0.0
–60
–50
–40
–30
–20
–10
0
10
20
30
40
50
60
Distance from Scan Center (mm)
Slice Sensitivity
Dose
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
12-31
LightSpeed ™ 4.X
1.25 mm, 1i mode
Head
1.0
Relative Dose
0.8
0.6
0.4
0.2
0.0
–60
–50
–40
–30
–20
–10
0
10
20
30
40
50
60
Distance from Scan Center (mm)
Dose
Slice Sensitivity
0.63 mm, 2i mode
Thin Head
1.0
Relative Dose
0.8
0.6
0.4
0.2
0.0
–60
–50
–40
–30
–20
–10
0
10
20
30
40
50
60
Distance from Scan Center (mm)
Slice Sensitivity
Dose
12-32
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
QUALITY ASSURANCE
Figure 12-18 Profile Curve
5.0 mm, 4i mode & 2.5mm, 8i mode
Body
1.0
Relative Dose
0.8
0.6
0.4
0.2
0.0
–60
–50
–40
–30
–20 –10
0
10
20
Distance from Scan Center (mm)
30
40
30
40
50
60
Slice Sensitivity
Dose
2.5 mm, 4i mode & 2.5mm, 8i mode
Body
1.0
Relative Dose
0.8
0.6
0.4
0.2
0.0
–60
–50
–40
–30
–20
–10
0
10
20
Distance from Scan Center (mm)
50
60
Slice Sensitivity
Dose
1.25 mm, 4i Mode
Body
1.0
0.8
0.6
0.4
0.2
0.0
–60
–50
–40
–30
–20
–10
0
10
20
30
40
50
60
Distance from Scan Center (mm)
Dose
Slice Sensitivity
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
12-33
LightSpeed ™ 4.X
1.25 mm, 1i mode
Body
1.0
0.8
0.6
0.4
0.2
0.0
–60
–50
–40
–30
–20
–10
0
10
20
30
40
50
60
Distance from Scan Center (mm)
Dose
Slice Sensitivity
0.63 2i Mode
Body
1.0
0.8
0.6
0.4
0.2
0.0
–60
–50
–40
–30
–20
–10
0
10
20
30
40
50
60
Distance from Scan Center (mm)
Dose
Slice Sensitivity
Modulation Transfer Function (MTF)
1020.33 (C) ii same conditions as Noise
An MTF of 100% or 1.0 indicates no signal loss.
An MTF of 0.0 indicates total signal loss.
In practice, small, high contrast objects become impossible to resolve when MTF reaches the
0.05 – 0.02 range.
12-34
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
QUALITY ASSURANCE
Figure 12-19 MTF Curve
head and body
1.0
0.8
mtf
0.6
0.4
0.2
0.0
0
2
4
6
lp/cm
8
10
12
Maximum Deviation
In order to come up with “the maximum deviation,” manufacturers must imagine every
possible situation, however unlikely, that might occur within the entire user community.
Our statements of deviation include a maximum deviation to assure compliance with the
regulation, as well as a statement of expected deviations (2s) in the large majority of our
systems.
GE bases the expected deviations on the results of extensive multiple system testing.
Typical Dose 1020.33 (C) (2) i, ii and iii
Expected deviation equals +/-15%, except for the10 mA and 1.0mm techniques where
variation may be greater (up to a factor of two) due to the inherent deviation in small values.
Maximum deviation anticipated for tube output equals +/- 40%.
Dose Profile 1020.33 (C) (2) iv
The maximum deviation relating to dose profiles (FWHM or Full Width at Half Maximum)
should equal +/-30% or 1.5mm, whichever is larger.
This value includes variability inherent in the measurement of dose profile with TLD
(thermoluminescence dosimeter) chips.
The expected deviation equals +/-10% or 0.5mm, whichever is larger.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
12-35
LightSpeed ™ 4.X
Performance 1020.33 (C) (3)
Noise
The noise squared (s2) in a CT image is inversely proportional to the X-Ray dose.
The maximum deviation equals +/-15%.
Expected deviation equals +/-10%.
MTF
With the protocol used to generate the data reported here, expected deviations for values
on the MTF curve: +/-10%.
Maximum deviations may reach +/-20%.
Sensitivity Profile
With the protocol used to generate the data reported here, the slice sensitivity profiles
(FWHM) may vary +/-10% or 0.5mm whichever is larger.
Helical Scans: The slice sensitivity profile is triangular, and the FwHm may deviate by 20%,
or 1mm, whichever is greater.
With other methods, the maximum deviation may reach 1.5mm for all thicknesses; thin
slices are most affected by these measurement errors.
Radiation Protection
A qualified radiological health physicist should review scan room shielding requirements.
Consider equipment placement, weekly projected workloads, and materials used for
construction of walls, floors, ceiling, doors and windows.
The following illustrations depict measurable radiation levels within the scan room while
scanning a 32cm CTDI body phantom (body) and a 20cm water phantom (head).
Values, in millirems per scan, apply to both 60 and 50 hertz scanners.
12-36
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
QUALITY ASSURANCE
Figure 12-20 Typical Scatter Survey (Body Filter)
BODY SCATTER PHANTOM
ISO-CONTOUR LEVELS: 0.075, 0.15, 0.3, AND 0.6 mR/SCAN
Technique:
140 kV
100mA
1 Sec
4 x 5.00mm
0.075
0.15
0.3
0.6
0.6
0.3
0.15
0.075
50 Inches
127 cm
0
BODY SCATTER PHANTOM
0.075,
0.3, AND
0.6 mR/SCAN
ISO-CONTOUR LEVELS: 0.1,
0.20.15,
0.4 AND
0.8 mR/SCAN
Technique:
140 kV
100mA
1 Sec
4 x 5.00mm
0.075
0.15
0.3
0.6
0.6
0.3
0.15
0.075
0
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
50 Inches
127 cm
12-37
LightSpeed ™ 4.X
Figure 12-21 Typical Scatter Survey (Head Filter)
HEAD PHANTOM
ISO-CONTOUR LEVELS: 0.0375, 0.075, 0.15, AND 0.3 mR/SCAN
Technique:
140 kV
100mA
1 Sec
4 x 5.00mm
0.0375
0.075 0.15 0.3
0.3
0.15
0.075
0
0.0375
50 Inches
127 cm
HEAD PHANTOM
ISO-CONTOUR LEVELS: 0.0375, 0.075, 0.15, AND 0.3 mR/SCAN
Technique:
140 kV
100mA
1 Sec
4 x 5.00mm
0.0375 0.075 0.15 0.3
0.3
0.15
0.075
0
12-38
0.0375
50 Inches
127 cm
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
QUALITY ASSURANCE
Figure 12-22 .QA Master Data Form
QA Data Form
Contrast Scale
date:
Mean CT
#
Std. Dev.
plastic
High Contrast
Bar Size
Spatial Resolution
spec
37+/–4
Std. Dev.
1.6
1.3
1.0
water
0.8
difference
120+/–12
# of Visible Lines
Slice Thickness
5.0
W/L 100/+25
2.5
90/270 laser
1.25
W/L 100/–25
centered Y/N
EXT axial
3.75
W/L 100/50
Low Contrast
detectability
Alignment Light
Accuracy
INT axial
0 laser
W/L 100/–100
Top
CT #
Bottom
CT #
membrane
water
difference
smallest hole
W/L used (30/0)
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
Noise and Uniformity
spec:
Mean CT #
(Ctr. ROI)
0 +/– 3
Std. Dev.
(Ctr. ROI)
3.2+/– 0.3
Uniformity
(Ctr. MeanEdge Mean)
measurement:
0 +/– 3
12-39
LightSpeed ™ 4.X
This page intentionally left blank.
12-40
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
Performix Ultra X-Ray Tube Specif ications
Chapter 13
Performix Ultra X-Ray Tube
Specifications
Table 13-1 Tube Model and Catalog Numbers
Component
Model
Number
Catalog No.
Performix Ultra Tube Unit
2137130-4
D3182T
Performix Ultra Housing Assembly
2137130-2
N/A
Performix Ultra Insert
2120785-2
N/A
Environmental Specifications
Non-Operating Environment
Maintain a temperature range between -34°C and 60°C (relative humidity up to 95%
non-condensing) during storage and shipment of the tube unit.
Use GE Medical Systems transport packaging during shipment.
You may ship via commercial airlines.
Operating Environment
Maintain an ambient temperature of less than 35°C and 30 to 60% (non-condensing)
relative humidity (50% nominal) during operation
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
13-1
LightSpeed ™ 4.X
Diagnostic Source Assembly
Leakage Technique Factors
The leakage technique factors for the Performix Ultra Tube Unit, Model No. 2137130, with
Tube Collimator, Model No. 2020100.
•
140 kV
•
25.7 mA
Quality Equivalent Filtration
Performix Ultra Tube Unit
The aluminum equivalent filtration of the CT system with Performix tube consists of the tube
filtration plus fixed filtration in the collimator and the collimator adapter. All filtration is
permanent and cannot be removed by the user.
The “Quality Equivalent Filtration” of the CT system with Performix x-ray tube is 4.75mm of
aluminum. This is measured at 70 kV and in accordance with CE (IEC601-1-3:29.201) safety
and regulatory requirement.
CT Scan Ratings
These ratings apply to a system with computer controlled technique selection, scan mode,
and scan duration.
The system uses a math model to track tube temperature.
This tube cooling algorithm delays the start of a scan, if necessary, to avoid exceeding
temperatures that may damage the tube anode or unit.
There are two filters used in this system: one for head applications, and one for body
applications. When the body filter is selected, the ”Quality Equivalent Filtration” increases to
5.65mm of aluminum.
Table 13-2 Performix Target Load in Kilowatts for Selected Scan Technique
mA
13-2
80 kV
100 kV
120 kV
140 kV
40
3.2
4.0
4.8
5.6
70
5.6
7.0
8.4
9.8
100
8.0
10.0
12.0
14.0
120
9.6
12.0
14.4
16.8
140
11.2
14.0
16.8
19.6
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
Performix Ultra X-Ray Tube Specif ications
mA
80 kV
100 kV
120 kV
140 kV
170
13.6
17.0
20.4
23.8
200
16.0
20.0
24.0
28.0
210
16.8
21.0
25.2
29.4
230
18.4
23.0
27.6
32.2
240
19.2
24.0
28.8
33.6
280
22.4
28.0
33.6
39.2
290
23.2
29.0
34.8
40.6
340
27.2
34.0
40.8
47.6
350
28.0
35.0
42.0
49.0
360
28.8
36.0
43.2
50.4
380
30.4
38.0
45.6
53.2
400
32.0
40.0
48.0
na
420
na
42.0
50.4
na
440
na
na
52.8
na
NOTE: At 5mm slice, max mA for 140KV:
300mA SFOV Small
320mA SFOV Large
Performix Ultra Tube Assembly
Marking
The assembly carries two identification labels that list the model and serial numbers of the
tube insert and housing components, which comprise the tube assembly.
A third label certifies compliance with U.S.A. Federal regulation 21 CFR Sub chapter J, and
lists the date and place of assembly manufacture.
Reference Axis
Normal to the window center
Maximum Potential Difference
140 kVp
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
13-3
LightSpeed ™ 4.X
Principle Dimensions (with mounting bracket)
– Width50.6 cm
– Height82.4 cm
– Depth32.5 cm
Weight (without mounting bracket)
– 84 kg
Performix Ultra Tube Insert
– Length35.4 cm
– Diameter23.4 cm
Target Material
Tungsten - Rhenium focal track on a molybdenum alloy substrate backed by graphite
Maximum Potential Difference
140 kVp
Dual Focal Spots:
Small Focal Spot:
0.9mm (W) x 0.7mm (L) (Traditional Methodology)
0.7 (W) x 0.6 (L) Nominal Focal Spot Value (IEC 336/93)
Large Focal Spot:
1.2mm (W) x 1.2mm (L) (Traditional Methodology)
0.9 (W) x 0.9 (L) Nominal Focal Spot Value (IEC 336/93)
Target Angle
7 degrees
Rotor Speed
8000 RPM minimum
13-4
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
Performix Ultra X-Ray Tube Specif ications
Anode Heat Capacity
6.3 MHU / 4700 kJ
Figure 13-1 Performix Anode Cooling Curve
STORED ENERGY (KJ)
4700
4230
3760
3290
2820
2350
1880
1410
940
470
0
0
10
20
30
40
50
60
TIME (MINUTES)
NOTE: Cooling curves reflect maximum tube performance. System
software ultimately limits tube operation.
Serial Exposure Rating
Controlled by system software.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
13-5
LightSpeed ™ 4.X
Single Exposure Load Rating
Figure 13-2 Maximum Anode Input Power for Single Exposure Radiographic Ratings
kVp X mA per exposure (in thousands)
60.00
50.00
40.00
Lg – Spot
Sm –Spot
30.00
20.00
10.00
0.00
0.1
1
10
Maximum Exposure Time – Sec.
100
NOTE: Based on initial maximum storage of 1200 kJ.
13-6
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
Performix Ultra X-Ray Tube Specif ications
Figure 13-3 Large Spot Single Exposure Technic Limits
450
350
250
mA
150
50
80 kV
100 kV
120 kV
140 kV
0
0
10 20
30 40
50
60
70
Time – Sec.
80
90 100
110 120
Based on initial maximum storage of 383 kJ
NOTE: Large Focal Spot used for exposures over 24kW.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
13-7
LightSpeed ™ 4.X
Figure 13-4 Small Spot Single Exposure Technic Limits
300
250
200
mA
150
100
50
80 kV
100 kV
0
0
10 20
30 40
50
120 kV
140 kV
60
70 80
Time – Sec.
90 100
110 120
NOTE: Based on initial maximum storage of 383 kJ.
Performix Ultra Tube Assembly
Figure 13-5 Performix Tube housing Cooling Curve maximum ambient temperature = 35oC
Performix
Tube Housing Cooling Curve
4500
Stored Energy (kJ)
4000
3500
3000
2500
2000
1500
1000
500
0
0
10
20
30
Time (minutes)
40
50
60
NOTE: Cooling curves reflect maximum tube performance. System software ultimately
limits tube operation.
13-8
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
Performix Ultra X-Ray Tube Specif ications
Maximum Heat Capacity
– Housing5.5 MHU / 4100 kJ
– Insert6.3 MHU / 4700 kJ
Maximum Tube Assembly Heat Dissipation
3.7 kW
Focal Spot Modulation Transfer Function
•
1.2mm (W) x 1.2mm (L) and 0.9mm (W) x 0.7mm (L)
(Traditional Methodology)
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
13-9
MODULATION TRANSFER FUNCTION
LightSpeed ™ 4.X
MODULATION TRANSFER FUNCTION
WIDTH DIRECTION
1.2 mm W x 1.2 mm L FOCAL SPOT
STANDARD MAGNIFICATION 1.3
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
.1
.2
.3
.4
.5
.6
.7
.8
MODULATION TRANSFER FUNCTION
SPATIAL FREQUENCY – LINE PAIRS/mm
1.0
MODULATION TRANSFER FUNCTION
LENGTH DIRECTION
1.2 mm W x 1.2 mm L FOCAL SPOT
STANDARD MAGNIFICATION 1.3
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
.2
.4
.6
.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
SPATIAL FREQUENCY – LINE PAIRS/mm
13-10
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
MODULATION TRANSFER FUNCTION
Performix Ultra X-Ray Tube Specif ications
1.0
0.9
MODULATION TRANSFER FUNCTION
WIDTH DIRECTION
0.9 mm W x 0.7 mm L FOCAL SPOT
STANDARD MAGNIFICATION 1.3
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
.2
.4
.6
.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
MODULATION TRANSFER FUNCTION
SPATIAL FREQUENCY – LINE PAIRS/mm
1.0
0.9
MODULATION TRANSFER FUNCTION
LENGTH DIRECTION
0.9 mm W x 0.7 mm L FOCAL SPOT
STANDARD MAGNIFICATION 1.3
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
.2
.4
.6
.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
SPATIAL FREQUENCY – LINE PAIRS/mm
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
13-11
LightSpeed ™ 4.X
This page intentionally left blank.
13-12
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
Chapter 14
System Specifications
Table 14-1 Model Numbers
Component
Model Number
Gantry
(Scanner ID)
2281177 Gantry
w/MDAS
CT Operator
Computer Console
2266832-3 Console
w/MDAS
2341104 GOC1 Console
2350046 GOC2 Console
2377708 GOC3 Console
Table
Rating Plate Locations
FDA
(Y/N)
Lower, left Gantry base in
rear
Y
Rear of cabinet
Y
Y
Y
Y
Right side, low on front
leg
Y
N
Metal free Cradle &
Cradle Extender
2115993
Bottom angled surface,
front end
Performix Tube Unit
Tube Insert
Tube Housing
2137130-4
2120785-2
2137130-2
On Housing center
Collimator
2214768-2 Collimation
Tube at 12 o’clock: on
collimator front
Y
Power Distribution
Unit
2269902
Back horizontal surface of
top cover
N
QA phantom/20 cm
water
2144715
none
N
48 cm poly phantom
2144721-2
none
N
35 cm poly phantom
2144721
none
N
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
N
Y
14-1
LightSpeed ™ 4.X
Table 14-2 System Dimensions
Component
Gantry
Size (inches)
whd
Size (cm)
whd
Weight
(lbs)
Weight
(kg)
87.6 74.1 39.6
223 188.1 100.1
2800
1273
Octane
48.5 29-32.5 41
123 71.1-81.3 104.1
664
301
GOC1
49
26.75-34.75 Keyboard table,
26.75-31.75 Monitor table
40-48
123.8
68-88.3 Keyboard table,
68-80.7 Monitor table
102-122.8
370
167.8
GOC2
49
26.75-34.75 Keyboard table,
26.75-31.75 Monitor table
40-48
123.8
68-88.3 Keyboard table,
68-80.7 Monitor table
102-122.8
360
163
GOC3
49
26.75-34.75 Keyboard table,
26.75-31.75 Monitor table
40-48
123.8
68-88.3 Keyboard table,
68-80.7 Monitor table
102-122.8
395
180
Table & Cradle
24 44 199
61 112 505
750
340
Power Distribution Unit
30 50 23
762 1270 585
900
408
Total Weight with Computer Console Octane
6483
2940
Total Weight with Computer Console GOC1
6189
2807
Total Weight with Computer Console GOC2
6179
2802
Total Weight with Computer Console GOC3
6214
2819
Computer
Console
Helical High-Contrast Spatial Resolution
Scan Technique: 0.5 to 1-second gantry rotation, 120 kVp, 10 to 440 mA, 0.5625:1
acquisition mode with .625 mm to 10mm nominal image thickness, 1.875 mm to 35 mm
table travel/rotation, 25 or 50 cm scan FOV, 512 recon.
Standard (25-cm DFOV/Standard Algorithm):
14-2
•
0.584mm limiting resolution
•
4.0 lp/cm @ 50% MTF
•
6.5 lp/cm @ 10% MTF
•
8.5 lp/cm @ 0% MTF
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
System Specif ications
High-Res (10-cm DFOV/Edge Algorithm):
•
0.324mm limiting resolution
•
8.5 lp/cm @ 50% MTF
•
13.0 lp/cm @ 10% MTF
•
15.4 lp/cm @ 0% MTF
Line pair values decrease with larger focal spot (by 5% with Standard and by 7% with Edge);
limiting resolution is unaffected.
Measurement Basis: Limiting resolution is determined by reconstruction filter cutoff. The
50% and 10% MTF are demonstrated on GE Performance Phantom. MTF is calculated from
a two-dimensional Fourier transform of the point spread function using pixel data around a
0.05mm tungsten wire.
Axial High-Contrast Spatial Resolution
Scan Technique: 0.5 to 4.0 sec scan time, 120 kVp, 10 to 440 mA, 0.625 mm to 10 mm
nominal image thickness, 25 or 50cm scan FOV, 512 recon.
Standard (25 cm DFOV/Standard Algorithm):
•
0.584mm limiting resolution
•
4.0 lp/cm @ 50% MTF
•
6.5 lp/cm @ 10% MTF
•
8.5 lp/cm @ 0% MTF
High-Res (10 cm DFOV/Edge Algorithm):
•
0.324mm limiting resolution
•
8.5 lp/cm @ 50% MTF
•
13.0 lp/cm @ 10% MTF
•
15.4 lp/cm @ 0% MTF
Line pair values decrease with larger focal spot (by 5% Standard and by 7% with Edge);
limiting resolution is unaffected.
Measure Basis: Limiting resolution is determined by reconstruction filter cutoff. The 50% and
10% MTF are demonstrated on GE Performance Phantom. MTF is calculated from a
two-dimensional Fourier transform of the point spread function using pixel data around a
0.05mm tungsten wire.
Helical Low-Contrast Detectability - Statistical
On 8 inch (20 cm) CATPHAN phantom: 5mm @ 0.30% at 13.3 mGy (1.33 Rad).
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
14-3
LightSpeed ™ 4.X
Suggested Scan Technique:
120 kVp, 60 mAs, 0.5 to 1.0 second gantry rotation, 0.625:1 pitch mode with 10mm nominal
image thickness, 12.5mm table travel/rotation, 25 cm scan FOV, 25 cm display FOV, 512
recon, and standard algorithm.
On 8 inch (20 cm) CATPHAN phantom: 3mm @ 0.30% at 37.2 mGy (3.72 Rad).
Suggested Scan Technique:
120 kVp, 180 mAs, 0.5 to 1.0 second gantry rotation, 0.625:1 pitch mode with 10mm nominal
image thickness, 12.5mm table travel/rotation, 25 cm scan FOV, 25 cm display FOV, 512
recon, and standard algorithm.
Test method is as follows:
1. Measure mean CT # values of an array of pixel groups who’s area (pixel group) equals
the size of the detectable object size.
2. Calculate the standard deviation for the means of the pixel groups.
3. Statistically calculate the % contrasted change needed to insure with 95% confidence
that an object with this contrast could be detected with the above background noise,
and 95% confidence that it’s not detected when not present.
Measurement Basis: Dose is measured on top surface of the phantom using a pencil probe
with a 10 cm chamber length, with the phantom and probe held stationary, and with scan
time equal to time needed to acquire 30 images in helical mode. Dose is average dose per
image for 30 contiguous images (+/- 15% expected deviation).
Axial Low-Contrast Detectability - Statistical
On 8 inch (20 cm) CATPHAN phantom: 5mm @ 0.30% 13.3 mGy (1.33 Rad).
Suggested Scan Technique:
120 kVp, 100 mAs, 0.5 to 1.0 second gantry rotation, axial acquisition mode with 10 mm
nominal image thickness, 25 cm scan FOV, 25 cm display FOV, 512 recon, and standard
algorithm.
On 8 inch (20 cm) CATPHAN phantom: 3mm @ 0.30% at 37.2 mGy (3.72 Rad).
Suggested Scan Technique:
120 kVp, 280 mAs, 0.5 to 1.0 second gantry rotation, axial acquisition mode with 10 mm
nominal image thickness, 15 mm table travel/rotation, 25 cm scan FOV, 25 cm display FOV,
512 recon, and standard algorithm.
Test method is as follows:
1. Measure mean CT# values of an array of pixel groups who’s area (pixel group) equals
the size of the detectable object size.
2. Calculate the standard deviation for the means of the pixel groups.
14-4
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
System Specif ications
3. Statistically calculate the % contrasted change needed to insure with 95% confidence
that an object with this contrast could be detected with the above background noise,
and 95% confidence that it’s not detected when not present.
Measurement Basis: Dose is measured on top surface of the phantom using a pencil probe
with a 10 cm chamber length, with the phantom and probe held stationary. (+/- 15%
expected deviation).
Helical Image Noise:
0.32% +/-0.03% at 28.5 mGy (2.85 Rad)
Suggested Scan Technique:
120 kVp, 160 mAs, 0.5 to 2.0 second gantry rotation, 0.625:1 pitch mode with 10mm nominal
image thickness, 12.5mm table travel/rotation, 25 cm scan FOV, 25 cm display FOV, 512
recon, and standard algorithm.
Measurement Basis: Noise is demonstrated on 8.5 in AAPM water phantom or GE Quality
Assurance phantom using 25mm x 25mm box ROI. Dose is measured on top surface of the
phantom using a pencil probe with a 10 cm chamber length, with the phantom and probe
held stationary, and with scan time equal to time needed to acquire 30 images in helical
mode. Dose is average dose per image for 30 contiguous images (+/- 15% expected
deviation).
Axial Image Noise:
0.32% +/-0.03% at 29.3 mGy (2.93 Rad)
Suggested Scan Technique:
120kVp, 260 mAs, 0.6 to 4.0 second gantry rotation, 10mm nominal image thickness, 2i
mode reconstruction, 25 cm scan FOV, 25 cm display FOV, 512 recon, and standard
algorithm. Dose is dose per image.
Measurement Basis: Noise is demonstrated on 8.5 in AAPM water phantom or GE Quality
Assurance phantom using a 25mm x 25mm box ROI. Dose is measured on top surface of the
phantom using a pencil probe with a 10 cm chamber length (+/- 15% expected deviation).
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
14-5
LightSpeed ™ 4.X
Dose Performance
Helical Dose
CTDI expressed in mGy):
CTDI expressed in mGy/100 mAs:
Head
43.4 mGY center
43.0 mGy surface
Head
18.1 mGy/100 mAs center
17.9 mGy/100 mAs surface
Body
14.2 mGy center
25.7 mGy surface
Body
5.9 mGy/100 mAs center
10.7 mGy/100 mAs surface
CTDI100 expressed in mGy (Rad);
CTDI100 expressed in mGy/100 mAs:
Head
45.8 mGy (4.20 Rad) center
47.8 mGy (4.327 Rad) surface
Head
19.1 mGy/100 mAs center
19.9 mGy/100 mAs center
Body
13.9 mGy (1.27 Rad) center
28.3 mGy (2.60 Rad) surface
Body
5.8 mGy/100 mAs center
11.9 mGy/100 mAs surface
CTDIw expressed in mGy (Rad):
CTDIw expressed in mGy/100 mAs:
Head
47.0 mGy (4.35 Rad)
Head
19.6 mGy/100 mAs
Body
23.8 mGy (2.18 Rad)
Body
9.9 mGy/100 mAs
Scan Technique:
120kVp, 240 mAs, 0.5 to 1.0 second gantry rotation, 16 x 1.25 , pitch 0.9375:1,
18.75mm/rotation, 10mm slice thickness.
Measurement Basis: Helical CTDI, CTDI100, and CTDIw dose calculated from measured axial
CTDI, CTDI100, and CTDIw data and adjusted for 0.9375:1 scan mode and 240 mAs. Dose is
average dose per image for 30 contiguous images (+/- 15% expected deviation).
Axial Dose
CTDI expressed in mGy:
Head
44.2 mGY center
43.6 mGy surface
Head
17.0 mGy/100 mAs center
16.8 mGy/100 mAs surface
Body
14.2 mGy center
26.1 mGy surface
Body
5.5 mGy/100 mAs center
10.0 mGy/100 mAs surface
CTDI100 expressed in mGy (Rad);
CTDI100 expressed in mGy/100 mAs:
Head
46.5 mGy center
48.6 mGy surface
Head
17.9 mGy/100 mAs center
18.7 mGy/100 mAs surface
Body
14.0 mGy center
29.1 mGy surface
Body
5.4 mGy/100 mAs center
11.2 mGy/100 mAs surface
CTDIw expressed in mGy (Rad):
14-6
CTDI expressed in mGy/100 mAs:
CTDIw expressed in mGy/100 mAs:
Head
47.8 mGy
Head
184 mGy/100 mAs
Body
24.2 mGy
Body
9.3 mGy/100 mAs
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
System Specif ications
Scan Technique:
120kVp, 260 mAs, 0.5 to 1.0 second gantry rotation, 16 x 1.25, 10mm nominal image
thickness, 2i mode reconstruction. Dose is dose per image.
Volumetric Helical Scan Image Quality
With LightSpeed being the first sub-millimeter isotropic CT scanner, GE Medical systems has
defined new specifications: Coronal and Sagittal Image Quality:
1. Visual Measurement
Reformatted resolution is demonstrated on the Nuclear Associates AAPM High Contrast
Resolution Insert #76-413.
Scan technique is 120kVp, 100 mAs, 0.5 sec scan rotation, 16 x 0.625mm, 0.562:1 pitch,
5.625mm/rotation, 25 cm SFOV, 10 cm DFOV, Detail Algorithm.
An effective 0.5mm voxel size is clearly seen in coronal and sagittal views (2nd smallest
resolution group).
2. Statistic Measurement
Volumetric MTF is computed from the X, Y, and Z axis of a 0.2mm bead using sagittal and
coronal images of the 8¨ Catphan, MTF module with bead source #CTP445.
Scan technique is 120kVp, 100 mAs, 0.5 sec scan rotation, 16 x 0.625mm, 0.562:1 pitch,
5.625mm/rotation, 25 cm SFOV, 10 cm DFOV, Detail Algorithm.
MTF (z-axis) is 12.4 1p/cm @ 10%, 151p/cm @ 0% which is 0.33mm limiting resolution.
MTF (X, Y, & Z)
X &Y
Z
% modulation
100
80
60
40
20
0
0
5
10
15
lp/cm
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
14-7
LightSpeed ™ 4.X
Subsystem Specifications
Operator Console
•
Size: 48 in (1220mm) wide x 33.5 in (851mm) deep x 49.5 in (1260mm) high
•
Front and back work surfaces can be set during installation within a range of vertical
heights that help accommodate a variety of siting requirements.
or
Operator Console GOC1 or GOC2
•
Size: 49 in (1238mm) wide x 40-48 in (1022-1228mm) deep x
29-32.5 in (711-813 mm) high
Host Computer
Octane Based System
•
Silicon Graphics, Inc. Octane 2 Workstation
•
1-2 MIPS CPU with 2 MB cache.
•
64-bit microprocessor. Single/Dual R12000A processor with Direct 3D option.
•
RISC architecture
•
34.6/40.3 SPECfp95 (1P/2P)
•
22.9 SPECint95 (1P)
•
295 SPECfp2000
•
311 SPECint2000
•
512 MB ECC SDRAM standard. 1.5GB total with the Direct3D option.
PC Based System
•
HP XW8000 Technical/Graphics Workstation
•
Dual SMP 2.66 GHZ Intel Xeon Processors with 512KB L2 cache
•
Intel Hyper-Threading Technology (4 logical processors)
•
2GB DDR266 ECC Dual Channel Memory Standard (4.2 GB/sec)
•
SPECfp2000 >900
•
SPECint2000 >900
Image Processor
•
Silicon Graphics, Inc. Octane SI or Enhanced SI IMPACT Graphics Engine.
or
14-8
•
Silicon Graphics, Inc. VPRO V12-DCD Graphics Engine with 128 MB SDRAM
•
104 MB TRAM (Texture Memory)
•
448 Million trilinear textured interpolations per second
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
System Specif ications
or
•
Nvidia Quadro4 980XGL AGP 8X graphics with 128MB Memory
•
Graphics Processor Unit (GPU) Clock 300Mhz
•
Graphics Memory Clock 325Mhz
•
Dual 350Mhz Video RAMDAC's
Image Reconstruction Engine (Pegasus)
•
Custom-designed special purpose CT Image Generator
•
Pipelined parallel processing allows 12 views to be back-projected simultaneously
•
GE-patented IG ASICS provides 7.5 GFLOPS for back projection and IBO acceleration
•
32-bit floating point data format
•
IG DSP’s rated at 1900 MFLOPS
Image Reconstruction Engine (Global Recon Engine)
•
Custom-designed, scalable, special purpose CT Image Generator
•
Pipelined parallel processing allows 12 views to be back-projected simultaneously
•
Image Generator consisting of:
– Dual SMP 2.8 GHz Intel Xeon Processors with 512 KB L2 Cache
– Intel Hyper-threading Technology (4 Logical Processors)
– 2 GB DDR 266 ECC Dual Channel Memory Standard (4.2 GB/s)
•
32-bit floating point data format
The LightSpeed 4.X Operator Console user interface features:
•
Two, large 20 inch or 21 inch monitors
– Scan/recon monitor mainly for scan and recon control with no image display
– Image monitor mainly for image display, analysis, processing, and management
– Each monitor provides a 1280 x 1024 high resolution, flicker-free display
•
Scan control keyboard assembly with intercom speaker, mic and volume controls
•
Three button mouse with mouse pad
•
BrightBox (trackball assembly)
•
Two wide work surfaces
16-Row Detector
•
16 rows x 888 active patient elements; 15 reference elements
•
70% geometric efficiency
•
99% absorption efficiency
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
14-9
LightSpeed ™ 4.X
16-Row DAS
•
16 rows x 758 active patient channels; 3 reference
•
4, 3, 2, 1, 0.9, 0.8, 0.7, 0.6, 0.5 second scan
•
984 - 1640 views per second
Table
Load Capacity
•
180 kg (400 lbs) with +/- 0.25mm positional accuracy guaranteed
•
205 kg (450 lbs) maximum allowed with normal operation and +/- 1mm positional
accuracy
Maximum Cradle Travel
•
1703mm
•
Table Height, Gantry Tilt and scanning software determine the Scannable range
Cradle Speeds
•
100mm/sec (scout imaging)
•
1.25 - 33.5mm/gantry rotation (helical imaging)
Scan Location Accuracy
+/- 0.25mm
Elevation Travel Time
FAST < 30 seconds
Full Range
SLOW < 120 seconds
Elevation Accuracy
+/- 1.5mm
Elevation Range
516mm to 991mm above the floor
Gantry
Tilt Limits
+30° to -30°
Tilt Speed
60 degrees/min nominal
14-10
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
System Specif ications
Gantry Opening Diameter
700mm
Isocenter to Tube Distance
541mm
Tube Focus to Detector Distance
949mm
Rotational Speeds
360 degrees in 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3 and 4 seconds
Rotational Freedom
1
continuous rotate
X-Ray Tube
Performix
Heat Storage
•
Anode: 6.3 MHU / 4700 kJ
•
Housing: 5.5 MHU / 4100 kJ
Focal Spots
Dual Focal Spots
Small Focal Spot
•
0.9mm (W) x 0.7mm (L) (Traditional Methodology)
•
0.7mm (W) x 0.6mm (L) Nominal Focal Spot Value (IEC 336/93)
Large Focal Spot
•
1.2mm (W) x 1.2mm (L) (Traditional Methodology)
•
0.9mm (W) x 0.9mm (L) Nominal Focal Spot Value (IEC 336/93)
Anode
•
Target angle: 7 degrees
•
Up to 53.2 kW maximum radiographic load
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
14-11
LightSpeed ™ 4.X
Laser Alignment Lights
Maximum Output Power
<1.0 mW/laser beam
Power Supply
5 volt
Maintenance
•
Laser alignment lights do not require user maintenance.
•
Qualified service personnel must inspect the lights quarterly to assure proper
alignment.
Generator Subsystem Specifications
Main Power Supply
Line Voltage
•
Nominal: Taps selections of 380 to 480 V in 20 V Steps
•
Daily Variation: Nominal +/- 8%
3-Phase 50/60 Hz +/- 0.5 Hz
•
Phase-to-phase balance within 2% of lowest phase-to-phase voltage.
•
Line regulation 6% or less at 90 kVA, 85% P.F.
Maximum 3-Phase Power Demand at Full Rated Output
90 kVA
Maximum Line Current Demand
108A @ 480 V
Maximum line current demand defined at 140 kV and 380 mA.
Generator Rating and Duty Cycle
The gantry contains a high frequency generator and on board computer control
Maximum Power
53.2 kW power
kV Choices
80, 100 120, 140 kV
14-12
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
System Specif ications
Maximum mA
440
Regulation
Recovery within 2 kV for 10% line variation in 50msec
Rise Time
< 2 msec, to attain 75% of selected value
Fall Time
< 10 msec to fall below 75% of selected value
Generator Duty Cycle
The generator duty cycle is determined by the tube protection algorithm based on tube
type used.
kV, mA, and Time Accuracy
Kilovolts
kV Selections
80, 100, 120, and 140 kV
Basic kVp Accuracy
+ 3% +/- (3% + 2kV)
Excludes first 10msec of exposure
kVp During First 10 ms
Basic accuracy (see above) +/- 5 kV
Milliamperes
mA Selections
10 to 440 mA, by 5 mA increments
•
Patient scanning subject to Scan limitations or 53.2 maximum
mA Accuracy
Patient scanning selections of 10 to 440 mA
Calibration scan selections of 10 to 30 mA +/- 4mA
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
14-13
LightSpeed ™ 4.X
Exposure Time
Normal Axial Scan Selections
0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, or 4 sec
Cine
Up to 120 seconds for a single continuous exposure.
Scout
•
Scan range 20 to 1600mm at 100mm/sec
•
Exposure time: 0.20 to 16.0 sec (exposure time increases proportionally with scan
distance selection)
Helical (Continuous scans)
Up to 120 seconds for a single continuous exposure.
Accuracy
•
1.8 to 60.0 second exposures: +/- 5% + 10 ms
Measuring Tool Variance
kV
The above stated accuracies are subject to additional variation due to calibration and
measurement instruments.
kV: +/- 5%
mA
mA: +/- 5%
Exposure Time
Time: +/- 3%
Accuracy Subject to Following Conditions
Line Voltages
•
Line voltage in specified range for nominal system voltages of 380 to 480.
•
Line to line voltages balanced within 2%.
Line Regulation
6% or less.
14-14
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
System Specif ications
Transient Voltage Variations Caused by External Loads Must Not:
•
Exceed 5%
•
Exceed 5 cycles duration
•
Occur more than 10 times per hour
To comply with the requirements of 21 CFR 1020.30, accuracies are stated in terms of
maximum theoretical deviation from selectable operating parameters for all technique
factor combinations.
For radiation output, the coefficient of variation is less than 0.05 for successive exposures
with constant technique factors.
Measurement Basis
Kilovolts
Precision 10,000:1 voltage dividers built into system reduce generated anode and cathode
voltages.
Resulting low voltage signals provide continuous closed-loop control of the average kV.
Signals are noise filtered and periodically monitored by the computer system.
Operator console displays monitored values during calibration.
Precision 1000:1 voltage divider, model 46-154966G1, (Catalog # C1515A) provides external
feedback during calibration.
•
Calibrate Anode and Cathode signals separately.
•
Use a calibrated dual channel oscilloscope with a divider for reference.
•
Check calibration of the low voltage kV measuring circuits.
•
Average kV values measured by the system are slightly lower than the peak kV during
exposure, due to high frequency ripple in the HV power supplies.
•
The difference amplitude, a function of kV and exposure current, always falls within the
stated kVp accuracy.
Milliamperes
Precision shunt resistors, built into the system, measure the tube current component
returned from the secondaries of the
high-voltage transformers.
•
The resulting signals provide continuous closed-loop control of the average mA.
•
Signals are noise filtered and periodically monitored by the computer system
•
Operator console displays the monitored values during calibration.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
14-15
LightSpeed ™ 4.X
Check calibration of the shunt resistors and the low voltage mA measuring circuits with a
calibrated digital milliammeter.
Calibrate Anode and Cathode signals separately.
Exposure Time
Traditional Exposure time interval: Duration of time High voltage remains at or above 75% of
selected value.
LightSpeed 4.X Exposure time interval: Duration of the Expose Command signal within the
Stationary Controller, minus the HV rise time, plus its fall time with respect to the Expose
Command signal.
LightSpeed 4.X HV components reside on the gantry rotating base.
During stationary scans, use an oscilloscope to measure the HV rise and fall times, with
respect to the Expose Command signal.
Use the oscilloscope to measure the Expose Command signal during stationary scans, to
verify internal time measurements.
Use the internal timer to monitor time during axial/helical scans.
Environmental Specifications
Ratings and duty cycles of all subsystems apply if the site environment complies with the
following.
The specified environment must be constantly maintained, weekends, holidays, and
throughout the night.
Shutdown the CT system whenever the air conditioning fails.
Optional: Turn air conditioner OFF during CT shutdown for repair.
System Cooling Requirements
The cooling requirements do not include cooling for the room lighting, personnel, or non-CT
equipment present. Cooling requirements are listed by subsystem to allow planning for
each room of the CT suite.
Cooling requirements are given for minimum, recommended, and growth allowance
scenarios.
14-16
•
The minimum cooling figures assume patient throughput of 3 patients per hour and 75
scan rotations per patient.
•
The recommended cooling requirements assume patient throughput limited by the tube
cooling algorithm.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
System Specif ications
•
The suite cooling can be sized for future developments by using the growth allowance
figures. This cooling will accommodate more patients per hour and/or potential future
system enhancements.
Minimum Allowance
(Watts / BTU/Hr)
Subsystem
Gantry
Table
PDU
Operator Console
Xtream Operator Console
Optional Laser Camera
5440/18600**
330/11300
1000/3400
1320/4500
2165/7338
800/2730
Recommended cooling values should not be used for calculating system input
power requirements.
** Recommended Allowance: 7150/24400
Growth Allowance: 9200/31400
Temperature and Humidity Specifications
Ambient Temperature
Scan Room
70° - 75° F (21° - 26° C) for patient comfort
Control Room (including Console/Computer)
60° - 75° F (15° - 26° C).
Table and Gantry In Exam Room (when room is unoccupied)
60° - 75° F (15° - 26° C)
Equipment Room (if separate room to hold PDU)
60° - 84° F (15° - 29° C)
Rate of Change
5°F/Hr Max (3°C)
Room Temperature Uniformity
5°F Max Gradient (3°C)
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
14-17
LightSpeed ™ 4.X
Media (disks/tapes)
Keep long term storage media in the same temperature range as the computer, 60° - 75° F
(15° - 26° C).
Relative Humidity (All Areas)
•
30% - 60% (non-condensing) during operation, all areas.
•
Rate of Change 5% RH/Hr Max
NOTE: Use a temperature and humidity recorder to monitor the designated system area
during pre-installation and installation, to verify true temperature and humidity
conditions.
Electromagnetic Interference
Consult GE Medical Systems for recommendations when the peak 60 Hz/50 Hz field within
the gantry region exceeds 0.01 gauss peak.
Consider the following when trying to reduce suspected Electromagnetic Interference (EMI):
•
The external field strength from a source of magnetic field decreases rapidly with the
distance from the source.
•
A bank of three single phase transformers generates a smaller magnetic field (less
external leakage) than a three-phase transformer with an equivalent power rating.
•
Large electric motors generate substantial EMI.
•
Steel reinforcing in the building structure can act as an
effective conductor of EMI.
•
High powered radio signals can affect computers.
•
No substitute exists for proper screening of cables and cabinets.
Pollution
Individual components contain filters to optimize environmental conditions.
•
Keep air pollution to a minimum.
•
Keep the CT suite clean at all times.
•
Do not have dust and fume generating work near the system.
•
Keep component filters clean and free from obstructions
Carpeting
•
Install anti-static carpeting - or- treat existing carpets with an anti-static solution.
•
Static discharges affect operation and may cause system failures.
Do NOT use steel wool to clean tile floors in scan suite. Fine metal fibers can enter
enclosures and cause internal shorts.
14-18
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
System Specif ications
Lighting
Patient Comfort
Use a variable indirect light source between 20 – 100 foot candles in the scan room
Control Room
Select and position subdued light to reduce monitor reflections, and prevent operator eye
strain
Equipment Room
Provide a bright light source for use during maintenance.
Altitude
•
Minimum Altitude: 100 feet (30.5 meters) below sea level
•
Maximum Altitude: 7,500 feet (2287 m) above sea level
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
14-19
LightSpeed ™ 4.X
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14-20
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
Planned Maintenance
Chapter 15
Planned Maintenance
The following chart gives a description, and frequency of Planned Maintenance (P.M.)
procedures. Please refer to Direction 2141834-100 for the details of each P.M. procedure and
P.M. report charts. LightSpeed 4.X PMs are based on gantry revolutions.
PMs will be done every 250k gantry revolutions. The average LightSpeed 4.X scanner does
1,000,000 revolutions per year, therefore the average scanner has approximately four
Planned Maintenance activities per year.
Table 15-1 LightSpeed 4.X PM Schedule (based on 1000k revolution cycle/year)
SubSystem
Description
Schedule
A
Schedule
B
Schedule
C
Schedule
D
Console
Check for smooth rolling
trackball/mouse
X
X
X
X
Gantry
Check the number of gantry
revolutions
X
X
X
X
Gantry
Grease main bearing
X
Gantry
Check drive belt for wear
X
Gantry
Check scan and laser
windows
X
X
X
X
Gantry
Clean ventilation holes and
check fans
X
X
X
X
Gantry
Handling & removal of slip
ring brush debris
X
X
X
X
Gantry
Clean or replace tube fan
filter
X
X
X
X
Gantry
Slip ring vacuuming
X
X
X
X
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
15-1
LightSpeed ™ 4.X
SubSystem
Description
Schedule
A
Schedule
B
Schedule
C
High
Voltage
mA meter verification
X
High
Voltage
kV test (HHS) or
X
High
Voltage
HV tank feedback resistors
calibration
X
High
Voltage
Total kV measurement
X
High
Voltage
kV Meter verification
X
Schedule
D
Schedule A - PM Cycle begins when Revolution Counter shows xxx250k revolutions
Schedule B - Next 250k Revolutions when Revolution Counter shows xxx500k revolutions
Schedule C - Next 250k Revolutions when Revolution Counter shows xxx750k revolutions
Schedule D - Next 250k Revolutions when Revolution Counter increments a million
revolutions
Table 15-2 (cont’d.)LightSpeed 4.X PM Schedule (based on 1000k revolution cycle/year)
15-2
SubSystem
Description
Schedule Schedule Schedule Schedule
A
B
C
D
High
Voltage
Auto mA calibration
X
High
Voltage
mA and kV verification (HHS)
X
High
Voltage
Verify rise and fall times
(HHS)
X
High
Voltage
Verification of internal scan
timer (HHS)
X
PDU /
GPDU
Inspect/clean filter
PDU /
GPDU
Inspect fan operation
GPDU
Inspect 7 green indicator
lamps on GPDU
PDU
Check tightness of wire lugs
PDU
Inspect 4 green lamps (L1,
L2, L3, DCRGS status)
X
X
X
X
X
X
X
X
X
X
X
X
X
X
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
Planned Maintenance
SubSystem
Description
Schedule Schedule Schedule Schedule
A
B
C
D
PDU
Inspect 6 green lamps on
transformer assy
CRPDU
CRPDU PM checks
System
Verify emergency off
buttons (table/console)
X
System
Check X-Ray on lights (HHS)
System
Check operation of final
scan abort pushbuttons
System
Image performance QA
System
Monitor system logs
X
X
X
X
System
General cleaning
X
X
X
X
System
Update site log
X
X
X
X
Table
Upper assembly PM
X
Table
Lower assembly PM
X
Table
Check for wear or damage
on table extensions
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Schedule A - PM Cycle begins when Revolution Counter shows xxx250k revolutions
Schedule B - Next 250k Revolutions when Revolution Counter shows xxx500k revolutions
Schedule C - Next 250k Revolutions when Revolution Counter shows xxx750k revolutions
Schedule D - Next 250k Revolutions when Revolution Counter increments a million
revolutions
The Laser Camera is normally not considered to be part of the CT system. However, a
schedule for Planned Maintenance for the camera is included in the following table, and
procedures for Planned Maintenance for the GE Lasercamera are contained in the PM
Manual (Direction 2141834-100).
Table 15-3 Laser Camera
SubSystem
Laser
Camera
Description
3M Laser Camera
Maintenance
Quarter
1
X
Quarter
2
Quarter
3
Quarter
4
X
NOTE: Laser Camera PM’s are based on a Quarterly Schedule (2 PM’s per year) vs. PM’s which
are based on Gantry revolutions.
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
15-3
LightSpeed ™ 4.X
This page intentionally left blank.
15-4
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
Symbols
**Empty** 12-24
Numerics
4Row DAS
Subsystem Specifications 14-10
A
Address
CT Service Engineering 1-3
Alignment Light
Alignment Light Accuracy test 12-14
Subsystem Specifications 14-12
C
Calibration
General information 11-28
Channel Utilization Table - Plus Modes 11-25
Check Disk Space 8-1
Image space 8-1
Clever Gain Calibration 6-1
CT
General information 11-2
Operation Theory 11-2
CT Number
General information 11-30
Pixels and CT Numbers 11-34
System Performance 12-7
Window Level 11-35
Window Width 11-35
CT/i Performix X-Ray Tube
Tube Model and Catalog Numbers 13-1
X-Ray Tube Specifications See X-Ray Tube
Specification 13-1
D
Daily Fastcal Procedure 6-1
Daily Prep 6-1
DAS
Data Collection 11-22
Data Collection
General information 11-22
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
Data Storage
General information 11-28
Detector window 7-1
Disk Space 8-1
Disk space 8-1
Display
General information 11-29
Dosimetry and Performance
Maximum Deviation 12-35
MTF 12-34, 12-36
Noise 12-30, 12-36
Nominal Slice Thickness 12-30
Sensitivity Profile 12-36
E
Electromagnetic Interference 14-18
EMC
Glossary definition 3-6
EMI
Glossary definition 3-6
Environmen™al •pecifica™ions
Media s™orage 14-18
Environmental Specifications 13-1, 14-16
Altitude 14-19
Ambient Temperature 14-17
EMI 14-18
Lighting 14-19
Pollution 14-18
Relative Humidity 14-18
System Cooling Requirements 14-16
F
Fast Cal 6-1
Fast Calibration 6-1
Fastcal
Daily procedure 6-1
FPA Check Scans 6-1
G
Gantry
Subsystem Specifications 14-10
Index-1
General Information 11-1
Calibration Scans 11-28
CT Description 11-2
CT Number 11-30
CT Operation Theory 11-2
Data Collection 11-22
Data Storage 11-28
DFOV and Pixel Size 11-33
Filament Selection and Scan Thickness
11-22
Filament Selection Table 11-22
Focal Spot 11-22
Gray Scale 11-29
Image Display 11-29
Pixel Coordinates 11-31
Pixels 11-31
Pixels and CT Numbers 11-34
RAS coordinates 11-32
Reconstruction 11-24
Tube Warmup 11-3
Variables you cannot control 11-31
Window Level 11-35
Window Width 11-35
X-Ray 11-2, 11-3
X-Ray Tube Capacity See X-Ray Tube 11-21
Generator Specifications 14-12
Exposure Time 14-14, 14-16
Generator Rating and Duty Cycle 14-12
Kilovolts 14-13, 14-15
kV, mA and Time Accuracy 14-13
Main Power Supply 14-12
Measurement Basis 14-15
Measuring tool variance 14-14
Milliamperes 14-13, 14-15
Gray Scale
General information 11-29
H
Help
CT Applications phone number 1-2
GE CARES phone number 1-2
Index-2
I
Image Quality
Calibration and Scan Image Quality 12-3
Maintain image quality 5-1, 6-1
Phantom Image Test and Analysis
System Performance 12-7
QA Schedule
QA Procedure 12-3
System Performance
System Performance 12-4
Image Space 8-1
Image space 8-1
K
kV
Accuracy 14-13
accuracy 14-13
Measurement Basis 14-15
L
LaserCam
Planned Maintenance 15-3
Learning and Reference Manual 4-1
M
mA
Accuracy 14-13
Measurement Basis 14-15
Maintain Image Quality 12-4
Matrix
Pixel Coordinates 11-31
Media
Media Storage specifications 14-18
Model Numbers 14-1
Modulation Transfer Function (MTF)
MTF 12-34
MTF 12-34
Maximum Deviation 12-36
MTF test 12-9
Mylar ring 7-1
Mylar Window Check 6-1
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
N
Noise 12-29, 12-30
Maximum Deviation 12-36
P
Periodic Maintenance 15-1
Phantom
Alignment Light Accuracy test 12-14
Center Phantom in FOV 12-5
Contrast Scale test 12-7
High Contrast Spatial Resolution test 12-8
Low Contrast Detectability test 12-9
MTF test 12-9
Noise and Uniformity test 12-11
Phantoms and Procedures 12-29
QA Phantom description 12-1
Slice Thickness test 12-12
Test and Analyze QA Phantom Images 12-7
Phone numbers
CT Applications assistance 1-2
GE CARES 1-2
Pixels
DFOV and Pixel Size 11-33
General information 11-31
Pixel Coordinates 11-31
Pixels and CT Numbers 11-34
RAS Coordinates 11-32
Window Level 11-35
Window Width 11-35
Planned Maintenance
Console 15-1
Gantry 15-1
HV System 15-2
LaserCam 15-3
PM Schedule 15-1
Power Distribution Unit 15-2
System 15-3
Table 15-3
Prepare the System
Overview sheet 7-1
Q
QA 12-1
Position the phantom 12-4
QA Phantom 12-1
QA Procedure 12-1
Center QA Phantom in FOV 12-5
Copy the QA Data form 12-1
Prescribe the QA Series 12-5, 12-13, 12-15
QA Schedule 12-3
System Performance
System Performance 12-4
Typical Results & Variations 12-17
QA Schedule 12-3
Quality Assurance
Image Quality 12-1
QA Procedure 12-1
System Performance
System Performance 12-4
R
Radiation
HSA Standard Tube scatter survey
using body filter 12-37
Radiation Protection 12-36
RAS
Annotation 11-32
Coordinates 11-32
Reconstruction
General information 11-24
Reset 9-1
Reset Procedures 9-1
S
Safety
Radiation Protection 12-36
Scan Duration
Accuracy 14-14
Measurement Basis 14-16
Scan Thickness
Filament Selection Determines Range
11-22
Nominal Slice Thickness 12-30
Slice Thickness test 12-12
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
Index-3
Scan Time
Duration and accuracy 14-14
Sensitivity
Maximum Deviation 12-36
Space on Disks
Maintain Image Space 8-1
Spatial Resolution 12-8
Start Up 7-1
Subsystem Specifications
4Row DAS 14-10
Detector 14-9
Gantry 14-10
Generator Subsystem 14-12
Laser Alignment Lights 14-12
Table 14-10
X-Ray Tube 14-11
System Dimensions 14-2
System Performance 12-4
Alignment Light Accuracy 12-14
Analyze the QA Images 12-6
Contrast Scale 12-7
High Contrast Spatial Resolution 12-8
Low Contrast Detectability 12-9
Maintain Image Quality 12-4
Maximum Deviation 12-35
MTF 12-9, 12-34, 12-36
Noise 12-29, 12-36
Noise and Uniformity 12-11
Phantoms and Procedures 12-29
Radiation Protection 12-36
Sensitivity Profile 12-36
Slice Thickness 12-12
Typical Results & Variations 12-17
System Shutdown 9-1
Index-4
System Specifications
CT Scan Ratings 13-2
CT/i Performix X-Ray Tube See X-Ray Tube
Specifications 13-1
Diagnostic Source Assembly 13-2
Environment 13-1
Environment See Environmental
Specifications 14-16
Generator Subsystem 14-12
kV, mA and Time Accuracy 14-13
Measurement Basis 14-15
Measuring tool variance 14-14
Model Numbers 14-1
Performix Ultra Tube Assembly 13-3, 13-8
Performix Ultra Tube Insert 13-4
Subsystem Specifications See Subsystem
Specifications 14-8
System Dimensions 14-2
Target Load in Kilowatts table 13-2
System Warmup 5-1
T
Table
Subsystem Specifications 14-10
Temperature & Humidity Specifications 14-17
Tube Warmup 5-1
General information 11-3
Two hours elapse between exams 5-1
V
Variables you cannot control 11-31
W
Warmup 5-1, 6-1
Warmup Required 11-28
Window Level
General information 11-35
Pixels and CT Numbers 11-35
Window Width
General information 11-35
Pixels and CT Numbers 11-35
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
X
X-Ray
General information 11-2, 11-3
X-Ray Tube
Filament Selection 11-22
Filament Selection Table 11-22
Focal Spot 11-22
X-Ray Tube Capacity 11-21
X-Ray Tube Specifications 14-11
CT Scan Ratings 13-2
Diagnostic Source Assembly 13-2
Performix Ultra Tube Assembly 13-3, 13-8
Performix Ultra Tube Insert 13-4
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
Index-5
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Index-6
2351785-100 Rev. 7 (07/05)
© 2005 General Electric Company. All rights reserved.
g
GE Medical Systems
GE Medical Systems: Telex 3797371
9P.O. Box 414, Milwaukee, Wisconsin 53201 U.S.A.
(Asia, Pacific, Latin America, North America)
GE Medical Systems - Europe: Telex 698626
283, rue de la Miniére, B.P.34, 78533 Buc Cedex, France