In vivo quantitation of regional myocardial blood flow by positron-emission computed tomography

Abstract

The potential of positron-emission computed tomography (PTC) for external quantitation of myocardial indicator concentrations and regional myocardial blood flow (RMBF) and the effect of left ventricular wall thickness on tracer concentration recovery by PCT was examined in seven open-chest dogs. RMBF was determined by the arterial reference technique in vivo and in vitro. Together with gamma-emitting Ce-141 microspheres, positron-emitting Ga-68-labeled microspheres were injected into the left atrium and their myocardial concentrations determined in vivo from gated and ungated cross-sectional PCT images. The loss in count recovery related to object size was corrected using postmortem and in vivo echocardiographic left ventricular wall thickness measurements. In vivo measurements of RMBF by PCT correlated linearly with in vitro-derived RMBF (r = 0.98; n = 84), but they underestimated in vitro RMBF by an average of 40%. After correcting for wall thickness effect, in vivo measured RMBF agreed with the in vitro measurements in a one-to-one relationship (r = 0.99). The accurcy of the in vivo PCT measured RMBF was maintained when corrections for wall thickness were made from in vivo echocardiographic instead of from postmortem measurements. Gating of the PCT images improved the accuracy of the in vivo RMBF determinations. Moreover, the increase in regional count recovery during systole provided an estimate of systolic wall thickening. Changes in left ventricular wall thickness from end-diastole to end-systole measured by PCT closely correlated with the changes in wall thickness observed by echocardiography. We conclude that (1) myocardial indicator tissue concentrations,and thus, RMBF, can be accurately measured by PCT provided corrections are made for the effect of wall thickness on count recovery; (2) these corrections can be made using in vivo echocardiography; and (3) gated PCT imaging can be used to evaluate regional myocardial systolic wall thickening as an index of regional function and combined with measurements of RMBF or regional metabolism. The results represent a framework for the noninvasive measurement of RMBF and metabolism by PCT in the experimental animal and in man.