Estimation of Local Cerebral Glucose Utilization by Positron Emission Tomography: Comparison of [ 18 F]2-Fluoro-2-Deoxy-D-Glucose and [ 18 F]2-Fluoro-2-Deoxy-D-Mannose in Patients with Focal Brain Lesions

A comparative PET study of [¹⁸F]2-fluoro-2-deoxy-D-glucose (FDG) and [¹⁸F]2-fluoro-2-deoxy-D-mannose (FDM) uptake was performed in 13 patients with focal brain lesions. Differences between FDG and FDM with respect to model rate constants, lumped constant, and estimated metabolic rate for glucose were determined on a regional basis. Across whole brain, the transport rate constant K*₁ was almost unchanged, whereas k*₂, describing the transport back from tissue to plasma, was 6% higher, and the phosphorylation rate constant k*₃ was 9% lower for FDM compared to FDG. This implies a 20% lower lumped constant for FDM. No significant regional variability of this differential tracer behavior was observed in normal or in lesioned brain tissue. Thus, results from previous FDG studies, where the radiotracer was not 100% pure FDG but contained varying amounts of FDM, can easily be corrected by adjustment of the lumped constant employed in metabolic quantitation.