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Coronary CT Angiography:
Protocols -- Radiation Dose
James A. Brink, M.D.Yale University School of Medicine
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Number of
Procedures (millions)
% Collective dose (Person-Sv)
% Per capita (mSv)
Radiography 276 52 182,000 19 0.6
Interventional 13 2 112,000 12 0.4
CT 67 12 440,000 46 1.45
Mammography 34 6 3,300 < 0.5 0.01
Dental 125 23 2,300 <0.5 0.01
Nuclear Medicine 21 4 230,000 23 0.7
Total ~ 544 100 ~ 970,000 100 3.2
2006
Fred Mettler, MD: “Magnitude of Radiation Uses and Doses in the US:NCRP Scientific Committee 6-2 Analysis of Medical Exposures”
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Natural
NCRP 3.0
CT scanning 1.5 mSv
Radiography 0.6 mSv
Nuclear medicine 0.7 mSv
All other <1 mSv
Medical 3.2 mSv
Total ~ 6.2 mSv per capita
Medical 0.54 mSv
Total 3.6 mSv per capita
Natural 3.0 mSv
U.S. 1980 U.S. 2006
Interventional 0.4 mSv
Medical Radiation Exposure: 600% increase
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Adapted from Pierce, D.A. and Preston, D.L.
Excess Relative Risk for Cancer Mortality (1950-1990) in A-bomb Survivors (all ages)
0
0.02
0.04
0.06
0.08
0.1
0 20 40 60 80 100 120 140
Dose (mSv)Dose Range for CT
1 in 2000
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Risks
X-rays, gamma rays, and neutrons--labeled as known carcinogens by NIEHS on January 2005
A CT examination with an effective dose of 10 mSvmay be associated with an increase in the possibility of fatal cancer of approx. 1 chance in 2000. USFDA
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Cardiac CT Dose (mSv) Relative Dose
Chest x-ray 0.02 1Coronary Calcium:
EBT/MDCT 0.8/1-4 40/50-200Annual Background Rad. 3.6 180Coronary angiogram 3-10 150-500Coronary CTA
EBT 1.2 60MDCT(16) 9-14 450-700MDCT(64) 16 800MDCT(64 ”Triple”) 35 1,750
Adapted from Morin et al., Circ. 2003;107:917-922 and McCullough Herz 2003;28:1-6
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Retrospective Gating
-200ms 800ms
O-90%
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Pitch
Ella A. Kazerooni, AJR 2003
Pitch 1Pitch 1.5:1
Pitch 0.5:1
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Cancer Risk from CCTA
• Phantom Data and Monte Carlo Simulation– BEIR VII report from atomic bomb survivors– Lungs: 42 - 91 mSv (greatest LAR)– Breasts: 50 - 80 mSv– Lifetime Cancer Risks: w/ gating
» Male, age 80 1 in 3261 1 in 5017» Female, age 20 1 in 143 1 in 219
Einstein AJ, et al. JAMA. July, 2007; 298: 317-323 (Columbia U.)
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Technique
• Tube Current (mA)• Tube Voltage (kVp)• Beam Pitch• Recon. Algorithm• Dose Monitoring
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Tube Current Modulation
AEC:AutomaticExposureControl
Radiation Dose Savings of up to 50%
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ECG gating (Retrospective) +Tube Current Modulation
Radiation Dose Savings of 30-50%
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Prospective Cardiac Gating
Table move
Table move
X-ray on timeTarget Phase range
Retrospective Gated Helical Acquisition
Prospective Gated Axial Acquisition
Multiphase DataFunctional analysis
Single phase or phase rangeLow dose acquisition
6-15 mSv
3-6 mSv Diagnostic Cath: 3 - 5 mSv
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Prospective (Step and Shoot) ECG Gating
• 41 CCTA patients–GE 64DCT, prospective gating–Effective dose: 1.1-3.0 mSv (mean = 2.1)–Non-diagnostic image quality in 5%
» Step artifacts from lack of overlap» May require some overlap, dose increase
Husmann L, et al. (Univ. Hospital Zurich), Eur Heart J,12/07
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Women
• Breast Shields (?)–Bismuth latex–Several sizes–Attenuates primary beam–Little effect on image quality
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Breast Shields
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Breast Shields• Reduced dose to:
– breasts by 30% – lungs by 15%
• Increase in image noise• “Reduction in organ dose could be realized
more efficiently with a reduction in tube current”
Geleijns J et al. Quantitative assessment of selective in-plane shielding of tissues in CT. European Radiology 2006:16:2334-2340
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Low kVp -- Rationale
• K-edge of Iodine 32 keV
• Mean photon energy– 80 kVp 44 keV–100 kVp 52 keV–120 kVp 57 keV–140 kVp 62 keV
Huda W, et al. Radiology 2000; 217:430
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0
5
10
15
20
25
30
35
40
45
0 4 8 12 16 20 24 28 32 36
Phantom diameter, cm
140 kV
120 kV
100 kV
80 kV
Effect of kV on Dose
constant mAs (165)
Courtesy of Marilyn Siegel, MD
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0
10
20
30
40
50
60
0 4 8 12 16 20 24 28 32 36
Phantom diameter, cm
80 kV
100 kV
120 kV
140 kV
Effective of kV on Image Noise
Courtesy of Marilyn Siegel, MD
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0
50
100
150
200
250
300
350
400
0 4 8 12 16 20 24 28 32 36
Phantom diameter, cm
80 kV100 kV120 kV140 kV
Effect of kV on Iodine Contrast
Courtesy of Marilyn Siegel, MD
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Low kV
• CT Angio: Phantom/Human Study–80, 100, 120, 140 kVp
»91-94% increase in signal w/ 80 kVp»Reduced radiation dose by 25-50%»Equivalent 3-D renderings
Kalva, et al. JCAT 2005; 30:391-397
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Low kV
• Chest CT: Improved detection of PE–100 vs. 140 kVp–Reduced radiation dose by 3x
»140 kVp -- 10.4 mGy»100 kVp -- 3.4 mGy
Schueller-Weidekamm, et al. Radiology 2006;241:899
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Low kV
• Coronary CTA: 100 patients (≤ 85 kg)–Siemens Dual Source 64DCT–Retrospective gating–120 kVp / 330 mAs: 12.7 mSv–100 kVp / 330 mAs: 7.8 mSv–No significant impact on image quality
Pflederer T, et al. AJR 2009; 192:1045-1050
40%
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SSCT Spiral DSCT Flash Spiral
Thorax: 5 s, breath holdTriple rule-out: 20 s, 20 mSvPediatric: > 4s, sedationWhole body: > 10 s4D dynamic scans: 16 cm
Thorax: 0.6 s, breath hold optional Triple rule-out: 0.6 s, < 5 mSvPediatric: < 1s, no sedationWhole body: 4 s4D dynamic scans: 48 cm
Scan Scan
Siemens Dual Source Flash
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Courtesy of Friedrich-Alexander University Erlangen-Nuremberg - Institute of Medical Physics / Erlangen, Germany
Dual Source Flash - Cardiac
Temp Res. 75 msSpat Res. 0.33 mm0.35 s for 149 mm Rotation 0.28 s100 kV; 290 mAs0.9 mSv
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Single Source Dual Source
Dual Source – Dual Energy
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S1: 80 kVx 104
15
10
5
0 50 100 150
80 kV140 kV
photon energy (keV)
num
ber
of q
uant
a
0.4 mm Sn
+ SPS
140 kV + SPS
S2: 140 kV
Siemens Medical Systems
Dose equivalent to 120 kV scan
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Adaptive Statistical Iterative Recon. (ASIR)
Dose reduction of 35% to 65%GE Healthcare, Inc.
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ASIR: DLP=136 mGy-cm (2.0 mSv)
Noise: 23.2 ASIR 50 % – Noise: 13.7
GE Healthcare, Inc.
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Coronary CTA; 100 kVp
2008 – Retrospective Gating; No ASIRCTDIvol = 21.6 mGyEff. Dose = 28 mSv
2009 – Prospective Gating; 60% ASIRCTDIvol = 6.8 mGyEff. Dose = 4.5 mSv
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Dose Monitoring
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Gated; No Tube Current Modulation
Effective Dose = DLP x 0.016 mSv/mGy-cm= 54.4 mSv
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Effective Dose
Estimate effective dose from DLPRegion mSv / (mGy cm)Head 0.0023Chest .017Abdomen .015Pelvis .019
Jessen KA. Applied Radiation and Isotopes, 1999; 165-172(This method is used in the ACR CT Accreditation Program)