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 N-13-ammonia or C-11-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 (similar to350 g) by dynamic imaging with the Sherbrooke small animal PET scanner. Scans were acquired in list mode for N-13-ammonia and 11 C-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 N-13-ammonia and C-11-acetate data with three and four rate constants, respectively, plus blood volume. A reasonable agreement was observed between MBF estimates extracted from N-13-ammonia and C-11-acetate. MVO2 estimates, as given by the k(2) rate constant, were obtained with good reproducibility, indicating that myocardial metabolism can reliably be assessed concurrently with MBF using C-11-acetate. It is concluded that myocardial blood flow and oxygen consumption can be evaluated in rats with small animal PET scantiers through high-rate, list-mode, dynamic imaging and kinetic modeling of N-13-ammonia and C-11-acetate.