PET Quantitation of Myocardial Blood Flow

Abstract

Positron-emission tomography affords the noninvasive measurement of regional myocardial blood flow in units of milliliters of blood per minute per gram myocardium. With this capability, PET expands the diagnostic possibilities of more traditional nuclear medicine approaches for explaining the human heart’s function and for identifying abnormalities in cardiovascular disease. More conventional nuclear medicine approaches, eg, SPECT, delineate the relative distribution of myocardial blood flow at rest or during physical or pharmacologically induced stress. While accurately identifying flow-limiting coronary stenoses, their location, and extent, such evaluations of the relative distribution of myocardial blood flow have remained incomplete for two reasons. First, myocardial regions with the highest radiotracer uptake are defined as normal on the images when, in fact, they may be subtended by diseased coronary arteries. Second, evaluating only the relative distribution of myocardial blood flow may fail to uncover balanced coronary artery stenosis or identify coronary artery disease still without flow-limiting stenosis. The flow tracer may distribute homogeneously throughout the left ventricular myocardium, while myocardial blood flow in absolute units may be abnormal. It is now widely accepted that the majority of acute coronary events originate in coronary vessels without significant angiographic stenosis. Therefore, identification of such preclinical disease could prove clinically important.