State-of-the-Art SPECT/CT: Cardiac Imaging Ernest V Garcia*, PhD Endowed Professor in Cardiac Imaging Director, Nuclear Cardiology R&D Laboratory Disclosure: Dr. Garcia receives royalties from the sale of the Emory Cardiac Toobox Shares of Syntermed, inc Consultant/funding: Lantheus, GE, Progenics, Syntermed
SPECT/CT: Cardiac Imaging Outline Need for quantification Overcome visual misperception Need for absolute concentration Need for CT calcium scoring Advantages of SPECT/CT multimodality fusion Transmission CT for Attenuation Correction Need to account for resolution, noise, scatter, and absorption Challenge of corrections with low counts High Lesion Contrast vs. True Lesion Quantification
How well can you discern different shades of gray? Compare the squares labeled A and B. What is the relative intensity A/B? a) 1/1 b) 2/1 c) 3/1 d) 4/1 Square A appears darker than Square B but they are exactly the same. Our perception is influenced by local contrast, shadows, and many other factors. Figure source: Wikipedia. Original by Edward H. Adelson, unrestricted use allowed.
Why do we need quantitation? Rank the objects from lightest (1) to darkest (4). For example: a) 1-A; 2-D; 3-B; 4-C b) 1-(A, D); 3-B; 4-C c) 1-(A, D); 4-(B, C) d) 1-A; 2-D; 4-(B, C) e) 1-(A, B, C, D) All of the objects are the same shade. Our perception is influenced by local contrast. C B D A 4 1
Why do we need quantitation? Rank the objects from lightest (1) to darkest (4). For example: a) 1-A; 2-D; 3-B; 4-C b) 1-(A, D); 3-B; 4-C c) 1-(A, D); 4-(B, C) d) 1-A; 2-D; 4-(B, C) e) 1-(A, B, C, D) All of the objects are the same shade. Our perception is influenced by local contrast. C B D A 4 1
Quantitative Nuclear Cardiology: Inherently Digital and Quantitative Our imagers and thus images are either natively pixilated or easily transformed into a digital pixel array. Importantly, our myocardial pixel values are directly proportional to physiological parameters such as: Perfusion Function Metabolism Innervations
SPECT vs. Planar H/M ROIs/Ratios Rationale for SPECT Measurements Planar ROIs Medastinum = Tubular Heart = ellipse/tube Tomo ROIs Medastinum = sphere Heart = ellipsoid
Heart to Mediastinum Measurement* Axes of H ROI Radius of M ROI * Exact same ROIs for FBP, OSEM & DSP all reconstructions within ECTb
H/M Results 311/312 population (Ji Chen et al, JNC 2012, 19:92-9) (n = 926 HF / 90 controls)
What is relative quantification? : Display Myocardial Relative Counts = 100 % x Voxel counts Max counts Garcia et al. J Nucl Med 26: 17-26, 1985 Candell / Castell /Aguadé Eds. DOYMA. Barcelona 1998
Garcia et al, 1994, Principles of Myocardial Perfusion SPECT Imaging
Calcium CT Scoring nhlbi.nih.gov Diamond & Forrester, NEJM 1979, 300(24) 1355
Multimodality Image Fusion stand-alone CT scanners as well as hybrid SPECT CT and PET CT platforms. With appropriate techniques, the radiation dose associated with CAC scanning is minimal (~1 2 msv), which makes this test a low-risk option. 3 combining anatomy and function CAC scores provide into useful a unique prognostic data. display 4 The Anatomy over function or function over anatomy Multi-Ethnic Study of Atherosclerosis (MESA) involved 6,722 individuals with no known cardiovascular disease (median follow-up ~4 years). In comparison to participants without calcification (CAC score 0), those with a score >300 had a nearly sevenfold higher adjusted risk Intense debate is ongoing about of a major the coronary strengths event. and weaknesses of 5 Importantly, the presence the various technologies and of the coronary appropriateness calcification provided of predictive their clinical informa- use tion beyond that derived from the Framingham risk score. In a meta-analysis conducted by Sarwar et al., a CAC score of 0 was associated with an excellent long- Concept of one-stop shop with a single imaging modality General Approach Modality 2 Modality 1 term prognosis: cardiovascular event rates were 0.56% for asymptomatic and 1.80% for symptomatic patients, respectively, during follow-up (mean 51 months). 6 A point worthy of note is that the literature supporting use of CAC scores is primarily based on screening populations. The use of CAC score alone as a diagnostic tool development of approaches to integrate anatomical and perfusion imaging in symptomatic patients has not been advocated, as it is not specific for the diagnosis of obstructive CAD 7 and, in younger patients, may miss the presence of exclusively noncalcified plaques. 8 Despite the powerful prognostic data afforded by CAC scores, evidence that the use of such imaging biomarkers leads to improved outcomes is limited. 9 This lack of substantiation is related to the fact that studies addressing this question would be complex, unethical (they would require random allocation of patients with elevated CAC scores to less aggressive therapy, or even e a c Coronary anatomy Myocardial perfusion Figure 1 Examples of images obtained by techniques used to assess coronary anatomy and myocardial perfusion. Anatomical Fused assessment Display is possible with to no treatment), and would require a long follow-up a coronary angiography and b CT angiography. Myocardial perfusion imaging can period. Nevertheless, the literature suggests that identification of coronary atherosclerosis Registration by CAC scanning illustrates that coronary anatomy and myocardial perfusion imaging predominantly be performed with c SPECT and/ or PET and d cardiac MRI. e The Venn diagram does lead to lifestyle changes and the intensification of provide unique information. The data provided by these techniques do overlap to a medical therapies. Algorithms 10 12 small extent, but combinations of imaging modalities have the potential to offer complementary information. Abbreviation: SPECT, single-photon emission CT. CT angiography image vs surface Within the past 10 years, advances in technology have and noncalcified plaques, as well as to estimate the severity of any stenosis present (Figure 2). During the pro- enabled contrast-enhanced, registration electrocardiographically gated coronary CT angiography to visualize both calci fied cedure, intravenous contrast is administered and image rigid vs deformable registration NATURE REVIEWS CARDIOLOGY VOLUME 7 APRIL 2010 227 2010 Macmillan Publishers Limited. All rights reserved b d Blankstein et al, Nat Rev Cardiol, 2010
CTA-Derived Anatomy Original CTA Segmented CTA MAR a definition Faber et al. JNM 2004, 745-753
Image Fusion and Image Quantification MAR f definition Mapping of MPI-derived measures on anatomy Physiologic Mass at Risk Common Normal Myocardium Common Mass-at-Risk Anatomic Mass at Risk
Piccinelli et al, ICNC 2015, Madrid (abstract)
Emory03 CTA-derived Anatomy, Myocardial Mass, Coronaries Path rpda prcai prcaii prcaiii Coronary Reconstructed LAD, D1, LCX, rpda,prcai, prcaii, prcaiii LCX LAD D1
CT Transmission for Attenuation Correction Emission SPECT Aligned to Transmission CT
Benefits of SPECT Attenuation Correction In vivo vs. ex vivo Tc-99m regional myocardial activity concentration AC + PVC Diagnostic Improvement Meta Analysis 13 Published Articles n = 1327 AC NAC Sensitivity 88 88 AC NC Specificity 77 67 Normalcy Rate 92 75 Garcia EV, JNC 2007 14:16-24. PET = 100~1000 x SPECT s count sensitivity Da Silva AJ et al.. J Nucl Med. 2001 42(5):772-9.
Symbiotic effect of correcting for: Resolution, Noise, Scatter, and Attentuation Garcia et al, Principles of Atlas of Nuclear Cardiology (Dilsizian/Narula eds) (4 th edition)
Measurement of Absolute Myocardial Blood Flow Compartmental Modeling and Factor Analysis
Reduced Dose vs. Increased Efficiency Injected Dose REST STRESS TOTAL Acquisition Time Injected Dose Acquisition Time Effective Dose* Acquisition Time 370 MBq 4 min 1110 MBq 2 min 12 msv 6 min 185 MBq 8 min 555 MBq 4 min 6 msv 12 min 93 MBq 16 min 278 MBq 8 min 3 msv 24 min * Effective dose estimated from tissue dose coefficients using ICRP Publication 60 tissue weighting factors ASNC goal = radiation exposure < 9 msv In 50% of studies by 2014 JNC 2010;17:709-718
Design of new generation dedicated cardiac ultra fast acquisition scanners. Detectors Garcia et al, 2011, Cardiac Dedicated Ultrafast SPECT Cameras:. J Nucl Med; 52:210-217
High Lesion Contrast vs. True Lesion Quantification
Promise of Cardiovascular Molecular Imaging Integrates functional imaging and molecular probes Improves our understanding of the molecular basis of the CV system starting with small animals Allows the recognition of the pathogenesis of CV disease in specific patients Translates this new knowledge to development of diagnostic and therapeutic breakthroughs With nuclear cardiology the most likely modality to implement clinically Already resulting in major investments in our field These breakthroughs will allow us to detect and treat to reverse disease before permanent damage takes place
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