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

Abstract

Positron emission tomography (PET) using the tracer [18F]-fluorodeoxyglucose (FDG) is commonly used for measuring metabolic rate of glucose ( MRglc) in the human brain. Conventional PET methods (e.g., the Patlak method) for quantifying MRglc 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 MRglc calculated using the Patlak method were investigated, and a correction scheme based on measured arterial glucose concentration ( Gp) was evaluated. Typically, with a 40% rise in Gp over the duration of the PET study, the true MRglc varied by only 1%; however, the Patlak method overestimated MRglc by 15%. The application of the correction reduced this error to −2%. In general, the application of the correction resulted in values of MRglc consistently significantly closer to the true steady state calculation of MRglc independently of changes to the parameters defining the model.