Free fatty acid flux measured using [1-11C]palmitate positron emission tomography and [U-¹³C]palmitate in humans

PET radiopharmaceuticals can noninvasively measure free fatty acid (FFA) tissue uptake. Investigators often use PET scan-derived data to calculate FFA flux. We tested whether the [1-11C]palmitate PET measures of palmitate flux provide results equivalent to a continuous infusion of [U-13C]palmitate. Nine volunteers participated in study 1 to evaluate whether a rapidly (10-20 s) given bolus of [1-11C]palmitate affects calculated flux results. Thirty volunteers participated in study 2, which was identical to study 1 except that the [1-11C]palmitate bolus was given over 1 min. Volunteers in both studies also received a continuous intravenous infusion of [U-13C]palmitate. Plasma palmitate concentrations and enrichment were measured by liquid chromatographymass spectrometry. The PET/CT images were analyzed on a workstation running PMOD. Palmitate flux was estimated using PET time-activity curve (TAC) data from regions of interest in the left ventricle (LV) and aorta both with and without hybrid TACs that employed the 11CO2-corrected data for the first 5 min and the 11CO2-corrected blood radioactivity for the remainder of the PET scan. Palmitate flux in study 1 measured with PET [1-11C]palmitate and [U-13C]palmitate were not correlated, and the PET [1-11C]palmitate flux was significantly less than the [U-13C] palmitate measured flux. In study 2, the palmitate flux using PET [1-11C]palmitate hybrid LV models provided closer mean estimates of [U-13C]palmitate measured flux. The best PET calculation approaches predicted 64% of the interindividual variance in [U-13C] palmitate measured flux. Palmitate kinetics measured using [1-11C] palmitate/PET do not provide the same palmitate kinetic results as the continuous infusion [U-13C]palmitate approach.