HIGH-RESOLUTION PET IN CATS - APPLICATION OF A CLINICAL CAMERA TO EXPERIMENTAL STUDIES

A commercial high-resolution scanner designed for clinical PET studies was tested for its applicability to investigate cerebral metabolism and blood flow in cats. Methods: Cerebral blood flow, CMRO(2), CBV and CMR(glo) were determined repeatedly using O-15 steady-state oxygen methods and F-18-fluorodeoxy-glucose (FDG). Metabolic and blood flow images of 14 contiguous 3-mm PET slices were compared to histological sections in four control animals. In another six cats, hemodynamic and metabolic changes were followed by serial multi-tracer PET for 24 hr after permanent occlusion of the left middle cerebral artery (MCA). Pattern and extent of changes of the physiological variables were related to the final infarct verified in matched histological sections. Results: At spatial resolutions (FWHM) of 3.6 mm in transaxial planes and 4.0 mm axially, details of the gross anatomy of the cat brain were distinguished best in the FDG images. Cerebral blood flow, CMRO(2) and CMR(glo) values measured in the cortex, white matter and basal ganglia were in the range of common autoradiographic results. Immediately after MCA occlusion, there was widespread decrease in blood flow, but metabolism was preserved at values, which suggest viable tissue. With time, the areas of increased oxygen extraction fraction (OEF) moved from the center to the periphery of the MCA territory. Conclusion: High-resolution PET can be used for repeat, quantitative imaging of blood flow and metabolism in small animals such as the cat. After MCA occlusion, the changes in blood flow and metabolism can be followed over time and can be related to the final morphological lesion.