To BOLDly Go Where Positron Emission Tomography Has Been Before

Abstract

Atherosclerotic disease remains concealed for many years and becomes clinically overt only when the growth of atherosclerotic plaques and the adverse remodeling of the arterial wall reach a critical stage that results in impairment of blood flow, ischemia, and angina. Large epicardial arteries have a diameter ranging from a few millimeters to ≈500 μm and are visible at coronary angiography. Prearterioles (diameter from ≈500 to ≈100 μm) and arterioles (diameter <100 μm) are beyond the resolution of current angiographic systems and hence are not visible at angiography. Each compartment is regulated by distinct mechanisms, and vascular resistance is distributed in series along the coronary vascular bed.1 The oxygen supply to the myocardium is determined by arterial oxygen saturation and myocardial extraction, which are relatively fixed in normal perfusion conditions. At constant distending pressure, variations of flow in epicardial coronary arteries can be achieved by means of intracoronary injection of arteriolar vasodilators.2 Near maximal hyperemia can be achieved using coronary vasodilators such as adenosine or dipyridamole, which induce vasodilatation, mainly in the coronary microcirculation. The functional severity of a stenosis cannot be estimated by anatomic imaging such as x-ray coronary angiography or multislice computed tomography, and, in addition, diffuse atherosclerosis and extensive arterial remodeling may contribute to the dissociation of anatomic and functional measurements of coronary stenosis severity. Therefore, the functional significance of coronary stenoses can only be evaluated by measures of coronary flow, and commonly the flow reserve, which is the ratio of nonregulated maximum (hyperemic) and autoregulated (resting) flow. This characterization requires accurate quantitative measurements of pressure and/or flow and can be estimated invasively as fractional flow reserve2 or measured noninvasively with positron emission tomography (PET).3 Articles see p 32 and 41 The relationship between resting and hyperemic myocardial blood flow and severity of coronary …