Medical Imaging Group Study
January 19th, 2016
Staff: Prof David Parker, Dr Garry Tungate and Mr Jack Bishop
Acknowledgements Professor Peter Jones designed this GS and
has kindly allowed us to use his presentations and other material.
Overview
Organisation
Duration: 10 weeks, starting 19th January 2015.
Timetabled hours: Tues 2-6 pm, Thurs 2-6 pm, Fri 4-6 pm.
Location: Tues/Thurs Nuclear Lab (PTG-R11/12), Fri LAW-BOARD(220)
An extra 100 hours (approx.) required.
Items of assessment and deadlines
Management Plan (Group Mark) – 5% (Wed 27th Jan)
Worksheet (Individual Mark) – 15% (Mon 8th Feb)
Project Work (Individual Mark) – 20% (Personal statement: Fri 18th Mar)
Project Seminar (Sub-group Mark) – 10% (Thurs 19th Mar)
Viva (Individual Mark) – 10% (Tues 22th Mar / TBC)
Lab Books (Thurs 24th Mar)
Project Report (Individual Mark) – 40% (Thurs 24th Mar)
Introduction to the Medical Imaging Group Study
Group Structure
All activities are student organised
Staff available on request
Nominate a group leader / Project Manager
Decide on sub-groups (4-5 students) / Work Package leaders
See handbook guidance on Project Management
Project Manager is expected to be involved in one (or more) sub-groups
Work as a team; help each other; you are not in competition
Take your time to decide on sub-groups / Work Package leaders
Spend the first week or so scoping out the problem
It is important to identify all the tasks and prioritise
Introduction to the Medical Imaging Group Study
Medical Imaging Group Study
An “industry” Group Study
Originally introduced as part of an IOP / HE STEM initiative
Idea was to develop projects linked with an external industrial partner
Experience of working in a professional research environment
Our “industry” Partner
Medical Physics Department at UHB NHS Foundation Trust
Expertise: nuclear medicine (imaging and therapy)
This project focuses on potential advances in diagnostic imaging
Aims: better images; faster; lower dose to patient
Project is of genuine interest in the field of medical imaging
Staff: Prof David Parker, Dr Garry Tungate and Mr Jack Bishop
Prof Stuart Green (UHB), Dr Michael Wilson (UHB)
Introduction to the Medical Imaging Group Study
Medical Imaging
How it works
Medical Physics Department will present the problem to you
Project work will be carried out here in the Y3 Nuclear Laboratory
They act as both the customer and as consultants
You will present your results to them in your final seminar
They will contribute to your feedback, but not your marks
Proposed study areas
1. Imaging with Compton Cameras
Potential to achieve high resolution and high sensitivity with reduced patient dose
2. Pixelated sensor technology
Evaluate the performance of gamma-ray pixel sensors
(i) BGO PET camera detector
(ii) 4 channel PMT with Plastic scintillator.
Introduction to the Medical Imaging Group Study
Medical Imaging
Gamma (Anger) Camera
Organ emitting g-rays
Applications
1.
2.
3.
4.
Planar Imaging
Planar Dynamic Imaging
SPECT Imaging
Gated SPECT Imaging
Collimator
NaI crystal
PMT array
SPECT = Single Photon
Emission Computed
Tomography
Position logic
Computer
Problem: the collimator determines spatial resolution but limits sensitivity
Introduction to the Medical Imaging Group Study
SPECT
How it works
360o
180o
0o
sinogram
Introduction to the Medical Imaging Group Study
Compton Camera Concept
Example in 2-d
Compton scattering – energy of scattered photon depends on angle of scatter
Eg
Eg ¢ =
1+
Eg
mec
2
(1- cosq )
Compton formula
g2
q2
g1
q1
DE
E
Scattering plane
(Compton scattering)
Absorption plane
(Photoelectric effect)
Introduction to the Medical Imaging Group Study
Compton Cameras
Advantages
Wide field of view; no need for collimation;
Hence lower patient dose
No trade off between spatial resolution and sensitivity
1
3
In principle, 3-dimensional imaging without tomography
Disadvantages
2
3-dimensional case is complicated
Requires pixelated detectors – many readout channels
4
Design issues
Must work with commonly used radioisotopes?
What determines the image resolution?
What is the optimal choice of detector materials?
What is optimal geometry?
Will it work for extended objects?
Introduction to the Medical Imaging Group Study
99mTc
18F
– 140 keV
– 511 keV
Scintillator Materials
• Sodium Iodide - NaI(Tl)
Density [g/cm3]
Effective atomic number
Hygroscopic
Wavelength of emission max. [nm]
Refractive index @ emission max
Primary decay time [ns]
Light yield [photons/keV]
3.67
50
yes
415
1.85
250
38
• Other materials
LaBr3, LaCl3, BaF2, CeBr3, CsI, CaF2, BGO, CdWO4, Lu18Y2SiO5(Ce), Plastic…
http://www.crystals.saint-gobain.com/Scintillation_Materials.aspx
https://www.saint-gobain.co.jp/sites/default/files/download/pdf/Crystal
_SGC_Scintillation_Materials_and_Assemblies_Saint-Gobain.pdf
• Considerations
Compton cross section is proportional to Z
Photoelectric effect cross section is proportional to Z4 and Eg-3
Introduction to the Medical Imaging Group Study
Compton Scattering
• Klein-Nishina Formula
ds
µP(Eg ,q )2[P(Eg ,q )+P(Eg ,q )-1 -1+cos2 (q )]
dW
Arbitrary units
P(Eg ,q ) =
1
1+(Eg / mec2 )(1-cosq )
137Cs
Eg = 662 keV
Angle (degrees)
Introduction to the Medical Imaging Group Study
Simulation
• A simulation in ROOT
for(Int_t i=0; i<100000; i++) {
Double_t ephoton = egamma;
SC = cs->Eval(ephoton,0,"S");
SP = pe->Eval(ephoton,0,"S");
SR = rs->Eval(ephoton,0,"S");
Double_t mu = SC+SP+SR;
Double_t x = exp->Exp(1./mu);
hDepth->Fill(x);
Bool_t absorbed = kFALSE;
Bool_t interacted = kFALSE;
Int_t nc = 0;
while( !absorbed && x < 5.) {
interacted = kTRUE;
Double_t probability = prob->Rndm()*(SP+SC+SR);
if( probability <= SP ) {
ephoton = 0;
absorbed = kTRUE;
} else if( probability <= SP+SC ) {
ComptonScatter(&ephoton);
hEPhoton->Fill(ephoton);
nc += 1;
}
SC = cs->Eval(ephoton,0,"S");
SP = pe->Eval(ephoton,0,"S");
SR = rs->Eval(ephoton,0,"S");
mu = SC+SP+SR;
x += exp->Exp(1./mu);
}
if (interacted) {
DetectorResponse(egamma-ephoton);
if (absorbed) hNComptonPE->Fill(nc);
hNCompton->Fill(nc);
}
}
TGraphErrors
Photoelectric
TRandom
Compton
TH1I
0.24
TRandom
Rayleigh
TGraphErrors
TRandom
TH1I
Introduction to the Medical Imaging Group Study
0.03
0.01
I(x) = I(0)exp(-m x)
Simulation
• Comparison with data
129292 counts
~250 x 1000 counts
2” NaI(Tl) – Real data
At 662 keV, the probability of PE is
0.03/0.28 = 10.7%
Observed ratio is ~ 50%
Conclusion: size of detector matters
Introduction to the Medical Imaging Group Study
( N x C ) + PE
Possible Work Breakdown
Task 1 – Hardware / Software
Build a proof-of-principle Compton Camera using components in the nuclear lab
Explore image reconstruction for one/two point source(s) in 2/3 dimensions
Design and build the necessary analysis and reconstruction software
Task 2 – Software
Develop a simple Monte Carlo model of a Compton Camera
Study optimal detector placement; choice of detectors; size of detectors etc
Benchmark against measurements from the proof-of-principle device
Task 3 – Hardware / Software
Evaluate pixelated BGO Detector
Evaluate Plastic scintillator
Build Pixelated detector
Programming environment C++ / ROOT
Introduction to the Medical Imaging Group Study
Multiple images
• Previous years looked at on axis point source
• Last year saw problems with multiple sources
• Not yet looked in 3D
• Need quick results
• Can you solve all outstanding problems?
• Choices need to be made.
Introduction to the Medical Imaging Group Study
Practical details
Energy measurements
HV
*
source
Pre-amp
Amplifier
E  PC/MCA (Multi-Channel Analyser)
X-ray energy spectrum
Proportional counter
Tb X-rays – 50 keV, 44 keV
Ka
Kb
Introduction to the Medical Imaging Group Study
Practical details
Timing (coincidence) measurements
HV
HV
*
source
Pre-amp
Pre-amp
Amplifier
Amplifier
Energy
Discriminator
Discriminator
Time
Start
Time-to-Amplitude
Converter
(TAC)
DT
PC/MCA (Multi-Channel Analyser)
Delay
Stop
Could be used as initial setup
One detector used as a scatter detector; the other stops the scattered photon
Difficult to get energy sum information or add more detectors
Introduction to the Medical Imaging Group Study
Digital signal processing
Analogue versus digital
Charge
Sensitive
Preamp
Shaping
Amplifier
Energy
Peak
Sensing
ADC
Trigger
Fast out
Logic
Unit
DISC
Threshold
Position
Timing
TDC
Scalar
Counting
CAEN DT5724, 4 channel, 14 bit, 100 MS/s Digitiser
Digitiser
Charge
Sensitive
Preamp
A/D
DPP
Energy
Timing
Readout
Counting
Interface
Shape
High throughput
Introduction to the Medical Imaging Group Study
PC
Safety
Radioactive sources
Most g-ray sources are sealed; perfectly safe if handled intelligently
Open a, b sources – risk of contamination
You should not come into contact with these, but be aware they exist
Ask a demonstrator if unsure about anything
Keep your distance
Do not sit close to sources for long periods
Important
All sources to be checked out/in by a demonstrator
Sources must not leave the laboratory under any circumstances
Introduction to the Medical Imaging Group Study
Safety
Pb bricks
Use sensibly for background shielding
Beware of crushing injuries; do NOT overload bench;
Carry one at a time; wash hands after handling
High voltage
Check detector/documentation – do NOT exceed maximum
Do NOT connect/disconnect HV with HV switched on
Turn on/off HV gradually – detector may be damaged otherwise
Typical values: NaI 700-1000 V; check polarity
Detectors
Note that detectors are fragile – please handle with care
Introduction to the Medical Imaging Group Study
Resources
• We have use of R11 and R12
• R11 shared with PTNR so we should not disturb any experimental
equipment, but can use computers.
• R12 is for our sole use. Can use all equipment and leave it set up.
Detectors
NaI
CeBr3
LaCl3
LaBr3
Ge
BGO
Plastic
PMT
1
1
1
1
•
1.5
2
6
1
~2
array of crystals + 4PMTs
build your own
cluster of 4
Introduction to the Medical Imaging Group Study
3 inch
~2
Final Comments
Challenges
Output of digitiser is list mode
uses lots of memory
Need to be willing to write some analysis code
ROOT analysis framework is useful for histogramming
Need to design experiments that will give you the information you want
Lots of discussion / reading / thinking needed
Some references on Canvas to get you started …
We will be learning about these issues with you
Any questions?
Introduction to the Medical Imaging Group Study