PET/CT imaging of myocardial blood flow and arterial calcium: Putting the pieces together
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From the Massachusetts General Hospital, Harvard Medical School, Boston, MA. Reprint requests: Ahmed Tawakol, Massachusetts General Hospital, Harvard Medical School, Boston, MA; [email protected]. J Nucl Cardiol 2013;20:331–3. 1071-3581/$34.00 Copyright Ó 2013 American Society of Nuclear Cardiology. doi:10.1007/s12350-013-9702-6
relative differences in blood flow from rest to stress perfusion. Therefore, only the areas of most significant relative coronary flow impairment are visually apparent. Measurement of absolute MBF or CFR limits the risk of underestimating disease severity, as areas with low MBF or CFR will be identified as being abnormal regardless of the flow in other myocardial regions. The measurement of CFR provides additional opportunities for the assessment of coronary disease. For example, patients with no significant epicardial coronary disease may still have decreased CFR, consistent with impaired endothelial function or ‘‘small-vessel’’ disease. It has been shown that PET-derived CFR is reduced in diabetic patients without known CAD, implying underlying vascular dysfunction, and also is an independent predictor of cardiac events in this population.3 The detection of reduced CFR in either of these scenarios could result in a change in clinical management. In the patient with probable multi-vessel CAD, there is a lower threshold for consideration of invasive catheterization for confirmation of diagnosis and subsequent revascularization. In the latter case, aggressive risk factor modification and/or medical therapy should be contemplated. As PET MPI requires robust attenuation correction, hybrid PET/CT scanners have been developed in which the CT scan provides an accurate anatomic attenuation map. Although hybrid scanners were originally developed for CT attenuation correction and oncologic applications, there has been great interest in establishing whether non-contrast CT acquisition of calcium scoring data (which can be readily obtained during the same patient sitting) has an incremental benefit in risk stratification or cardiac event prediction. Before discussing the role of this form of ‘‘hybrid’’ imaging, it would be useful to first review the role that calcium scoring independently has in risk profiling and coronary event prediction. Coronary artery calcium (CAC) scoring has historically been used in asymptomatic, intermediate risk patients for assessment of cardiovascular risk. It has been shown to be a powerful marker of cardiovascular risk in intermediate risk populations and provides incremental value beyond traditional Framingham risk factors, C-reactive peptide, and carotid intimal medial thickness for prediction of cardiovascular events and 331
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Pursnani and Tawakol Putting the pieces together
mortality.4 The detection of an elevated coronary calcium score has been shown to have favorable effects on both initiation of preventive medical therapies, and also on downstream clinical events as seen in the St. Francis Heart Study.5-7 There is limited data, however, on calcium scoring
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