Measurement of regional cerebral glucose utilization with fluorine-18-FDG and PET in heterogeneous tissues: theoretical considerations and practical procedure.

Functional tissue heterogeneity, i.e., inclusion of tissues with different rates of blood flow and metabolism within a single region of interest, is an unavoidable problem with PET. Errors in determination of regional cerebral glucose utilization (rCMRglc) with [18F]FDG have resulted from the currently used simplifying assumption that all regions examined are homogeneous. We have established an optimal, yet practical procedure to minimize errors due to tissue heterogeneity in determination of rCMRglc. Effects of applying the three-rate constant kinetic model designed for homogeneous tissues with both dynamic and single-scan procedures and the Patlak plot were evaluated in normal subjects in experimental periods up to 120 min following tracer injection. The procedure with a single scan carried out any time within the interval between 60 and 120 min following tracer injection, combined with population average rate constants determined over a 120-min period, was found to be optimal for quantitative rCMRglc studies.