Noninvasive measurement of myocardial activity concentrations and perfusion defect sizes in rats with a new small-animal positron emission tomograph

Background - We explored the feasibility of measuring regional tracer activity concentrations and flow defects in myocardium of rats with a high spatial resolution small-animal PET system (microPET). Methods and Results - Myocardial images were obtained after intravenous ¹⁸F-fluorodeoxyglucose (¹⁸FDG) in 11 normal rats (group 1) and assembled into polar maps. Regional ¹⁸F activity concentrations were measured in 9 regions of interest and compared with tissue activity concentrations measured by well counting. In another 9 rats (group 2), myocardial perfusion images were acquired with ¹³N-ammonia at baseline and during coronary occlusion. On the polar maps recorded during coronary occlusion, the size of perfusion defects was measured as the myocardium with <50% of maximum activity and expressed as percent total myocardium and was correlated with the area at risk defined by postmortem staining. The diagnostic quality of ¹⁸FDG and ¹³N-ammonia microPET images was good to excellent; the images were easily assembled into polar maps. In group 1, regional ¹⁸F concentrations by microPET and postmortem were correlated linearly (r=0.99; P<0.01 for average and r=0.97; P<0.01 for regional concentrations). In group 2, perfusion defect sizes by microPET and postmortem were correlated linearly (P<0.01; r=0.93). Conclusions - The findings indicate the feasibility of noninvasive studies of the myocardium in rats with a dedicated small-animal PET-imaging device.