Assessment of myocardial metabolism with 11C-palmitate. Comparison with 123I-heptadecanoic acid.

Carbon-11 (11C)-palmitate is chemically identical to its physiological counterpart. After intravenous injection the myocardial distribution of 11C-activity can be measured accurately by positron emission tomography. Regions of decreased 11C-palmitate uptake can be readily identified and their size quantified. Results obtained in dogs with experimental coronary thrombosis and in patients with myocardial infarction indicate that positron emission tomography with 11C-palmitate allows non-invasive assessment of the metabolic recovery of the myocardium after lysis of the occluding coronary thrombus. There is experimental evidence that the rate of clearance of 11C-palmitate activity from the myocardium is related to oxidative fatty acid metabolism. In dogs, a restriction of the oxygen supply to the myocardium results in a decrease in the rate of 11C-clearance independently of whether myocardial perfusion is concomitantly reduced or not. Similarities in myocardial uptake and clearance exist between iodine-123 (123I)-heptadecanoic acid and 11C-palmitate. However, interpretation of the kinetics of the radio-iodinated fatty acid analogue has to take into account the different intracellular fate of the iodine label compared with the fatty acid structure.