Evaluation of two population-based input functions for quantitative neurological FDG PET studies

The conventional measurement of the regional cerebral metabolic rate of glucose (rCMRGlc) with fluorodeoxyglucose (FDG) and positron emission tomography (PET) requires arterial or arterialised-venous (a–v) blood sampling at frequent intervals to obtain the plasma input function (IF). We evaluated the accuracy of rCMRGlc measurements using population-based IFs that were calibrated with two a–v blood samples. Population-based IFs were derived from: (1) the average of a–v IFs from 26 patients (Standard IF) and (2) a published model of FDG plasma concentration (Feng IF). Values for rCMRGlc calculated from the population-based IFs were compared with values obtained with IFs derived from frequent a–v blood sampling in 20 non-diabetic and six diabetic patients. Values for rCMRGlc calculated with the different IFs were highly correlated for both patient groups (r≥0.992) and root mean square residuals about the regression line were less than 0.24 mg/min/100 g. The Feng IF tended to underestimate high rCMRGlc. Both population-based IFs simplify the measurement of rCMRGlc with minimal loss in accuracy and require only two a–v blood samples for calibration. The reduced blood sampling requirements markedly reduce radiation exposure to the blood sampler.