Measurement of coronary blood flow using rubidium 84 and the coincidence counting method : A critical analysis

Abstract

The concepts on which the coincidence counting method for the measurement of myocardial blood flow by using rubidium 84 are based were re-evaluated and critically analyzed. Contrary to recent reports from this laboratory, it was shown in the isolated dog heart that alterations in coronary blood flow resulted in a change of the mean extraction ratio. As flow increased, the myocardial extraction ratio of rubidium 84 decreased; an increase in the mean extraction ratio occurred when coronary flow was reduced. This does not invalidate the calculation of flow as obtained by extrapolation of the myocardial clearance to time zero; at this time, the extraction ratio is theoretically one, provided the myocardium is extracting all the isotope at this time. In addition, it was shown that the myocardial extraction ratio early in the experiment was not 100 per cent but averaged 63.5 per cent and probably signified the presence of anatomic or functional shunts. Therefore, it was suggested that the calculated flows should be referred to as nutrient or effective coronary flows. It was demonstrated that the radioactivity of blood in the cardiac chamber could be neglected in the calculation of the myocardial uptake of rubidium. 84 The observation was confirmed that nitroglycerin increases the myocardial uptake and/or flow in patients without coronary artery disease; it failed to do so in patients with coronary artery disease. Because of this different response to the administration of nitroglycerin, the coincidence method as used here is of diagnostic aid in the recognition of coronary artery disease.