CT Scanning – The Good, The Bad
and the Ugly
Mark J. Sands, MD
Vice Chairman, Imaging Institute
Clinical Operations and Quality
Objectives
• Discuss the applications of Computed Tomography
(CT) use to contemporary medical care
• Review the safety limitations of CT
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Evolution of Computed Tomography
Godfrey
Hounsfield 1973
Sir Godfrey
Hounsfield
Original EMI CT head scanner
Mayo Clinic, Rochester, MN, circa 1973
CT Scanning Update
Evolution of Computed Tomography
Siemens Somatom Definition Flash 2009
Courtesy of Siemens and the University Hospital
of Munich - Grosshadern / Munich, Germany
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Evolution of Computed Tomography
CT Scanning Update
CT Advantages (The Good)
• Highly Contrast sensitive – ordinary xray can discern
only metal (bone) – water (soft tissue) – fat – air
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CT Advantages (Additional Good)
•Good Spatial resolution - can sharply
discern two points from another
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CT Advantages (Really Good)
Volumetric acquisitions and 3D reconstructions
DSA
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CT Disadvantages (The Bad)
• X ray dose- ionizing radiation
• Often requires the use of iodinated contrast –
nephrotoxicity issues
• Expense
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Why CT this patient?
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Why not this patient?
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Radiation Dose - The Ugly
CT Scanning Update
CT Procedures Increase From 1993 to 2006
http://physics.rsna.org/section/default.asp?id=PHYSICS_01
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Contribution of CT to Diagnostic Imaging Dose
(2007)
Jeffrey T. Seabourn, MD, “Radiation Dose Consideration in CT Imaging”
CT Scanning Update
Radiation Effects
 Acute effect
– Skin redness (erythema)
– Hair loss (epilation)
– Cataracts
 Stochastic effect:
– Cancer
– Genetic
 In general, cancer risk is the main concern from CT
 Recent incidents from Cedars-Sinai (10/09) indicated, if
not done properly, CT can cause severe acute effects
epilation (“ CT haircut”)
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Image Quality: Usual Dose vs. Low Dose
Usual Dose Image Quality (~13.0
mGy)
Low Dose Image Quality
(~4.5mGy)
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16-SLICE MDCT
OLD
INTERMEDIATE
FINAL
QRM = 200 mAs
QRM = 200 mAs
QRM = 145 mAs
CTDIvol = 13.65
CTDIvol = 9.10
CTDIvol = 6.45
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MDCT Enterography
McFarland EG, Brink JA, et al. Radiology 2001; 218:375-383
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Contrast Induced Nephrotoxicity
Definition
Nephrotoxicity is attributed to radiologic iodinated
contrast media when there has been a sudden
deterioration in renal status after the administration
of a contrast media and no other etiology appears
likely from the clinical records.
•Rise in serum creatinine of 0.5 to 2 mg/dl or 20-50%
increase from baseline
•Is related to the degree of pre-existing renal disease
and hydration. Clinically significant nephrotoxicity
after administration of iodinated contrast media is
hi hl unusuall iin patients
highly
i
with
i h normall renall ffunction
i
• Pre-existing renal insufficiency (GFR <60) and
Diabetes are highest risk factors
•4.6% risk for CIN in pts with eGFR <40 (Thomsen HS
et al, Eur J Rad 2009)
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