Abstract
Coronary blood flow is regulated by anatomical, hydraulic, mechanical, and metabolic factors. 1 Myocardial perfusion depends on both the driving pressure gradient and the resistance of the vascular bed. Through autoregulation, the coronary bed maintains myocardial perfusion within a narrow range, despite wide fluctuations in coronary perfusion pressure. 2 Autoregulation of coronary blood flow is driven by changes in regional myocardial metabolism and oxygen consumption. Coronary artery stenosis may induce different alterations of the autoregulation of coronary blood flow, resulting in impairment in myocardial function such as myocardial ischemia, myocardial stunning, myocardial hibernation, and myocardial infarction. Different radiotracers may be used as means of assessing the impairment of myocardial function; the choice of which tracer must be used as a means of identifying this dysfunction should depend primarily on the clinical questions to be answered. Myocardial perfusion single-photon emission computed tomography (SPECT) with thallium-201‐ and technetium-99m‐labeled agents is a well-established modality for the evaluation of patients with suspected or known coronary artery disease (CAD).3-7 Furthermore, different positron emission tomography (PET) perfusion tracers may be used for the quantitative measurement of absolute or relative myocardial blood flow, such as nitrogen-13 ammonia, rubidium82 chloride, and oxygen-15 water. Moreover, considering that myocardial ischemia is associated with alterations in myocardial metabolism, the use of metabolic tracers has emerged as a useful approach in investigating the effects of CAD on myocardial metabolism. The tracers used as a means of assessing cardiac metabolism in patients with heart diseases are labeled fatty acids and fluorine-18 fluorodeoxyglucose (FDG). PERFUSION IMAGING AGENTS WITH SPECT Thallium-201
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