Noninvasive Measurement of Cerebral Metabolic Rate of Glucose Using Standardized Input Function

The purpose of this study was to propose and validate a method for the noninvasive measurement of cerebral metabolic rate of glucose (CMRGlc) by fluorodeoxyglucose (FDG) PET with a standardized input function (SIF) and an autoradiographic method. Methods: Plasma input functions, measured by intermittent arterial blood samplings after the intravenous injection of FDG, in 44 patients who had fasted for at least 6 h, were used to generate the SIF. The input function of each patient was normalized with the net injected dose (nlD) of FDG and body mass as indicated by body surface area (BSA) or body weight (BW). The SIF was generated as an average of 44 normalized input functions. The estimation of the input function and CMRGlc with SIF was validated in 10 additional patients, who underwent FDG PET after fasting for at least 6 h. CMRGlc was estimated with a simulated input function (IFsim) generated with the following equation: IFsim = SIF × (nlD/body mass). The estimated CMRGlc was compared with the measured CMRGlc. Results: Based on BSA, the percentage error of the area under the curve of IFsim was 3.5% ± 2.2%. The percentage error of CMRGlc was 2.9% ± 1.9% in gray matter and 3.4% ± 2.2% in white matter. A similar percentage error was obtained based on BW. Conclusion: The proposed method is noninvasive and accurate, and therefore Is clinically acceptable for measuring CMRGlc in patients in fasting states.