Cardiac CT Lowering the Dose Dramatically U. Joseph Schoepf, MD, FAHA, FSCBT MR, FSCCT Professor of Radiology, Medicine, and Pediatrics Director of Cardiovascular Imaging
Disclosures Consultant for / research support from Bayer Bracco General Electric Medrad Siemens
Is Cardiac CT Safe? Radiation
1 in 114 Cancer Risk from Cardiac CT
Realistic Risk in Actual Clinical Patients >100 consecutive patients @ MUSC (65% ) 10th % 41 years, median 59 years, 90th % 72 years 10th % 69 kg, median 91 kg, 90th % 116 kg Radiation risk to a typical, real life patient : Cancer incidence 0.12%, Cancer mortality 0.10% W. Huda et al. AJR 2010
Vast Uncertainties W. Huda
www.aapm.org
Cardiac CT: Evolution of Radiation Dose H. Alkhadi et al., Eur Radiol 2011
54 yo Woman, Equivocal SPECT, 100kV Scan, 4.6 msv Radiation Protection Low kv
47 yo Woman, Chest Pain, Equivocal SPECT, 2.4 msv Prospective ECG Triggering
2 nd Generation DSCT: Single Heart Beat CT 31 yo man with family hx +++, chest pain and abnormal SPECT Entire heart in one diastole = 270msec
2 nd Generation DSCT: Single Heart Beat CT 31 yo man with family hx +++, chest pain and abnormal SPECT
Entire Chest in Acute Chest Pain Patients 56 yo Acute chest pain 100 kv 1.4 msv thorax 0.67 s for 290 mm 0.75 ms temporal resolution
ECG Synchronized Thorax < 1 sec Entire chest in 670 msec
Simple Measures Go a Long Way 42 yo, Chest Pain, Equivocal SPECT, 80 kv Prospective Triggering No Padding 0.5 msv
Iterative Image Reconstruction Increased spatial resolution with FBP is directly associated with increased image noise and higher radiation exposure Iterative reconstruction techniques have been proposed for over 3 decades to improve CT image quality Iterative reconstruction has been shown to reduce image noise, decrease artifacts, and allow radiation dose reduction for various CT applications
Iterative Reconstruction for the Heart Improved signal / noise ratio Lower radiation dose Improved image quality (e.g. obese patients) Decreased artifacts (e.g. stents, implanted devices) G. Bastarrika et al., Radiology 2009
idose Projection space (raw data) De noise starved projections maximizing the likelihood functional (Poisson noise distribution model) Image space (pixels) De noise remaining uncorrelated noise through a local structure model fitting data variation analysis De noise projections Estimate noise distribution Structure anatomic model selection N Fit noisy local topology to noiseless structure model Best Fit? Noise control Y 20 Acquisition Courtesy JA Leipsic, UBC idose Images
idose An iterative reconstruction method designed to reproduce, in low dose CT images, the noise power spectrum found in standard dose FBP CT 80% FGIR 80% idose Goal is to allow use of a higher percentage of IR while maintaining a clinically acceptable image Courtesy JA Leipsic, UBC
ASIR Courtesy JA Leipsic, UBC
ASIR: Radiation Dose Reduction BASELINE n=753 ASIR n=247 ASIR+ PROTOCOL n=202 P Value All Studies Combined DLP (mgy x cm) Effective Dose (msv) 250 (171 336) 3.5 (2.4 4.7) Prospective studies 164 (136 250) 2.3 (1.9 3.5) 89 (57 121) 1.3 (0.8 1.7) Retrospective studies <0.001 <0.001 DLP (mgy x cm) 1229 (1114-1436) 864 (693-1171) 1007 (771-1207) <0.001 Effective Dose (msv) 17.2 (15.6-20.1) 12.1 (9.0-14.6) 14.1* (10.8-16.9) <0.001 ALL STUDIES DLP (mgy x cm) 266 (186-364) 186 (143-300) 93 (57-136) <0.001 Effective Dose (msv) 3.8 (2.6-5.1) 2.6 (2.0-4.2) 1.3 (0.8-1.9) <0.001 Courtesy JA Leipsic, UBC
Iterative Reconstruction in Image Space M. Renker et al., Radiology 2011
Reduced Image Noise in Obese Patients FBP IRIS M. Renker et al., JCCT 2011
Reduced Image Noise in Obese Patients M. Renker et al., JCCT 2011
80% Less Radiation Dose Same Noise M. Renker et al., JCCT 2011
IRIS: Reduced Stent Blooming Artifacts FBP IRIS M. Renker et al., JCCT 2011
IRIS: Reduced Calcium Blooming Artifacts M. Renker et al., Radiology 2011
IRIS: Reduced Calcium Blooming Artifacts FBP IRIS M. Renker et al., Radiology 2011
IRIS: Improved Specificity for Stenosis n = 55 Patients with Agatston Score >400 M. Renker et al., Radiology 2011
SAFIRE raw data domain image domain noise detection & subtraction hypothesis testing model based forward projection & comparison
SAFIRE: Reduced Image Noise A. Moscariello et al., Eur Radiol 2011
SAFIRE A. Moscariello et al., Eur Radiol 2011
SAFIRE: 50% Less Dose 65 patient study Routine ccta w FBP vs. 50% reduced dose reconstructed with SAFIRE A. Moscariello et al., Eur Radiol 2011
SAFIRE A. Moscariello et al., Eur Radiol 2011
Per segment Per patient Full Dose FBP Half Dose SAFIRE Full Dose FBP Half Dose SAFIRE Accuracy 96.6% 97.8% 93.8% 96.9% Sensitivity 93.5% 95.3% 100% 100% Specificity 97.0% 98.1% 89.2% 94.6% NPV 99.1% 99.4% 100% 100% PPV 79.3% 86.4% 87.5% 93.3% True positive 100 102 28 28 False positive 26 16 4 2 True negative 842 852 33 35 False negative 7 5 0 0
Summary Iterative reconstruction techniques at cardiac CT provide Massive reduction in image noise Substantial reduction of blooming artifacts Improved visualization of coronary artery stents Improved visualization of heavily calcified segments Significantly better specificity and PPV for stenosis detection = fewer unnecessary catheterizations Substantially reduced radiation requirements
schoepf@musc.edu