Correction for the Effect of Rising Plasma Glucose Levels on Quantification of MRglc with FDG-PET

Positron emission tomography (PET) using the tracer [18F]-fluorodeoxyglucose (FDG) is commonly used for measuring metabolic rate of glucose (MR(glc)) in the human brain. Conventional PET methods (e.g., the Patlak method) for quantifying MR(glc) assume the tissue transport and phosphorylation mechanisms to be in steady state during FDG uptake. As FDG and glucose use the same transporters and phosphorylation enzymes, changing blood glucose levels can change the rates of FDG transport and phosphorylation. Compartmental models were used to simulate the effect of rising arterial glucose, from normal to hyperglycemic levels on FDG uptake for a typical PET protocol. The subsequent errors on the values of MR(glc) calculated using the Patlak method were investigated, and a correction scheme based on measured arterial glucose concentration (G(p)) was evaluated. Typically, with a 40% rise in G(p) over the duration of the PET study, the true MR(glc) varied by only 1%; however, the Patlak method overestimated MR(glc) by 15%. The application of the correction reduced this error to approximately 2%. In general, the application of the correction resulted in values of MR(glc) consistently significantly closer to the true steady state calculation of MR(glc) independently of changes to the parameters defining the model.