Small-Animal PET Imaging of Isolated Perfused Rat Heart

The assessment of myocardial radiotracer kinetics, including cardiac extraction fraction and washout, requires the study of isolated perfused hearts to avoid analytic error due to tracer recirculation and systemic metabolites. Analysis of the isolated perfused rat heart by a high-resolution small-animal PET system may offer both reliable evaluation of cardiac tracer kinetics and tomographic images. Methods: An isolated perfused heart system was modified to accommodate the small PET gantry bore size. Isolated rat hearts were perfused via the Langendorff method under a constant flow of Krebs-Henseleit buffer containing F-18-FDG with a rate of 5 mL/min and placed in the field of view of the commercially available small-animal PET system. Dynamic PET imaging was then performed, with F-18-FDG uptake in the isolated perfused heart verified by gamma counter measurements. Additionally, a rat heart of myocardial infarction was also studied in this system with static PET imaging. Results: Dynamic PET acquisition of the isolated heart under constant F-18-FDG infusion demonstrated continuous increase of activity in the heart. Correlation between cardiac activity (MBq) measured with the PET system and measurements made with the gamma counter were excellent (R-2 = 0.98, P < 0.001, n = 10). Tracer input rate (MBq/min) was also well correlated with cardiac tracer uptake rate (MBq/min) (R-2 = 0.87, P < 0.001, n = 12). PET imaging of the heart with myocardial infarction showed a clear tracer uptake defect corresponding to the location of scar tissue identified by autoradiography and histology. Conclusion: Combining the Langendorff method of isolated rat heart perfusion with high-resolution small-animal PET allows for the reliable quantification of myocardial tracer kinetics. This novel assay is readily adapted to available small-animal PET systems and may be useful for understanding myocardial PET tracer kinetics.