Cardiac studies in rats with 11C-acetate and PET: a comparison with 13N-ammonia

Regional myocardial blood flow (MBF) can be assessed noninvasively with dynamic positron emission tomography (PET) and ¹³N-ammonia or ¹¹C-acetate. The latter can also be used to estimate the myocardial oxygen consumption (MVO2) from the same time-activity curve. In this work, we explore the feasibility of such techniques for evaluating myocardial parameters in normal and ischemic rats (∼350 g) by dynamic imaging with the Sherbrooke small animal PET scanner. Scans were acquired in list mode for ¹³N-ammonia and ¹¹C-acetate as two consecutive 15-min dynamic scans separated by a 5-min interval, without moving the rat from the scanner. Regions of interest (ROIs) were defined on four segments of the myocardium to extract the time-activity curves. Three-compartment models were applied to fit the ¹³N-ammonia and ¹¹C-acetate data with three and four rate constants, respectively, plus blood volume. A reasonable agreement was observed between MBF estimates extracted from ¹³N-ammonia and ¹¹C-acetate. MVO2 estimates, as given by the k₂ rate constant, were obtained with good reproducibility, indicating that myocardial metabolism can reliably be assessed concurrently with MBF using ¹¹C-acetate. It is concluded that myocardial blood flow and oxygen consumption can be evaluated in rats with small animal PET scanners through high-rate, list-mode, dynamic imaging and kinetic modeling of ¹³N-ammonia and ¹¹C-acetate.