Feasibility of planar myocardial carbon 11-acetate imaging

Myocardial oxygen consumption can be determined by using carbon 11-acetate (11C-acetate) and positron emission tomography (PET). The aim of this study was to validate planar 11C-acetate scintigraphy in healthy individuals by relating the myocardial clearance rate of dynamic 11C-acetate scintigraphy with the rate-pressure product, which is used as a measure of cardiac work. Also, the optimal curve-fitting procedure of the time-activity curve and the intraobserver and interobserver variation of determining the clearance rates were assessed.

Six subjects were studied at rest, and seven subjects were studied during dobutamine stimulation. Imaging was performed with a planar camera equipped with high-energy collimators for 45 minutes after the injection of 185 MBq of 11C-acetate. Myocardial time-activity curves were corrected for decay. During the study, heart rates and blood pressures were measured to calculate the rate-pressure product. Myocardial time-activity curves showed a clear biphasic pattern. Clearance rates were expressed in k values. The best fitting procedure, as assessed by means of the lowest error of k and the best correlation with the rate-pressure product, proved to be a monoexponential fit on the first part of the time-activity curve (kmono). Subjects studied during dobutamine infusion had significantly higher rate-pressure product (15.0 +/- 2.1*10(3) vs 8.6 +/- 1.2*10(3), P < .001) and 11C-acetate clearance rates (kmono = 0.0657 +/- 0.0110 vs 0.0313 +/- 0.0056, P < .0001) than subjects studied at rest. There was low intraobserver and interobserver variation in determining kmono values. A significant correlation between the rate-pressure product and the monoexponential clearance rate was found (kmono = 5.11*10(-6)*RPP-0.012; r = 0.94, P < .001).

The estimation of myocardial oxygen consumption is feasible with planar 11C-acetate scintigraphy. Clearance rates and the relation with the rate-pressure product are similar to those reported in PET studies. This technique may be used for the assessment and follow-up of global myocardial metabolic abnormalities, eg, in patients with hypertensive heart disease, cardiomyopathy, myocarditis, and valvular disease.