Cardiac CT Lowering the Dose Dramatically

Transcription

1 Cardiac CT Lowering the Dose Dramatically U. Joseph Schoepf, MD, FAHA, FSCBT MR, FSCCT Professor of Radiology, Medicine, and Pediatrics Director of Cardiovascular Imaging

2 Disclosures Consultant for / research support from Bayer Bracco General Electric Medrad Siemens

3 Is Cardiac CT Safe? Radiation

4 1 in 114 Cancer Risk from Cardiac CT

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6 Realistic Risk in Actual Clinical Patients >100 consecutive 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

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8 Vast Uncertainties W. Huda

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10 Cardiac CT: Evolution of Radiation Dose H. Alkhadi et al., Eur Radiol 2011

11 54 yo Woman, Equivocal SPECT, 100kV Scan, 4.6 msv Radiation Protection Low kv

12 47 yo Woman, Chest Pain, Equivocal SPECT, 2.4 msv Prospective ECG Triggering

13 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

14 2 nd Generation DSCT: Single Heart Beat CT 31 yo man with family hx +++, chest pain and abnormal SPECT

15 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

16 ECG Synchronized Thorax < 1 sec Entire chest in 670 msec

17 Simple Measures Go a Long Way 42 yo, Chest Pain, Equivocal SPECT, 80 kv Prospective Triggering No Padding 0.5 msv

18 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

19 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

20 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

21 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

22 ASIR Courtesy JA Leipsic, UBC

23 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 ( ) 3.5 ( ) Prospective studies 164 ( ) 2.3 ( ) 89 (57 121) 1.3 ( ) Retrospective studies <0.001 <0.001 DLP (mgy x cm) 1229 ( ) 864 ( ) 1007 ( ) <0.001 Effective Dose (msv) 17.2 ( ) 12.1 ( ) 14.1* ( ) <0.001 ALL STUDIES DLP (mgy x cm) 266 ( ) 186 ( ) 93 (57-136) <0.001 Effective Dose (msv) 3.8 ( ) 2.6 ( ) 1.3 ( ) <0.001 Courtesy JA Leipsic, UBC

24 Iterative Reconstruction in Image Space M. Renker et al., Radiology 2011

25 Reduced Image Noise in Obese Patients FBP IRIS M. Renker et al., JCCT 2011

26 Reduced Image Noise in Obese Patients M. Renker et al., JCCT 2011

27 80% Less Radiation Dose Same Noise M. Renker et al., JCCT 2011

28 IRIS: Reduced Stent Blooming Artifacts FBP IRIS M. Renker et al., JCCT 2011

29 IRIS: Reduced Calcium Blooming Artifacts M. Renker et al., Radiology 2011

30 IRIS: Reduced Calcium Blooming Artifacts FBP IRIS M. Renker et al., Radiology 2011

31 IRIS: Improved Specificity for Stenosis n = 55 Patients with Agatston Score >400 M. Renker et al., Radiology 2011

32 SAFIRE raw data domain image domain noise detection & subtraction hypothesis testing model based forward projection & comparison

33 SAFIRE: Reduced Image Noise A. Moscariello et al., Eur Radiol 2011

34 SAFIRE A. Moscariello et al., Eur Radiol 2011

35 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

36 SAFIRE A. Moscariello et al., Eur Radiol 2011

37 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 False positive True negative False negative

38 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

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