Whole-Body Biodistribution, Dosimetry, and Metabolite Correction of [(11)C]Palmitate: A PET Tracer for Imaging of Fatty Acid Metabolism

INTRODUCTION: Despite the decades long use of [(11)C]palmitate positron emission tomography (PET)/computed tomography in basic metabolism studies, only personal communications regarding dosimetry and biodistribution data have been published. METHODS: Dosimetry and biodistribution studies were performed in 2 pigs and 2 healthy volunteers by whole-body [(11)C]palmitate PET scans. Metabolite studies were performed in 40 participants (healthy and with type 2 diabetes) under basal and hyperinsulinemic conditions. Metabolites were estimated using 2 approaches and subsequently compared: Indirect [(11)C]CO(2) release and parent [(11)C]palmitate measured by a solid-phase extraction (SPE) method. Finally, myocardial fatty acid uptake was calculated in a patient cohort using input functions derived from individual metabolite correction compared with population-based metabolite correction. RESULTS: In humans, mean effective dose was 3.23 (0.02) µSv/MBq, with the liver and myocardium receiving the highest absorbed doses. Metabolite correction using only [(11)C]CO(2) estimates underestimated the fraction of metabolites in studies lasting more than 20 minutes. Population-based metabolite correction showed excellent correlation with individual metabolite correction in the cardiac PET validation cohort. CONCLUSION: First, mean effective dose of [(11)C]palmitate is 3.23 (0.02) µSv/MBq in humans allowing multiple scans using ∼300 MBq [(11)C]palmitate, and secondly, population-based metabolite correction compares well with individual correction.