Validation of an analytic method of calculating cerebral glucose metabolism using PET

Quantitative modeling of cerebral metabolic rate for glucose (CMRglc) using PET with the FDG method requires calculation of the integral of the time c ourse of radioactivity in arterial plasma. Numeric integration has typicall y been used but requires 30 or more blood samples taken between 15 s and 10 0 min after injection of the radiotracer. Our laboratory has developed an a lternative integration method that fits the values of the plasma samples to an analytically integrable function using only 4-6 samples taken between 4 0 and 110 min after radiotracer injection. Methods: The plasma integrals we re calculated by both the analytic and the numeric methods with data from F DG PET studies that were not used in the development of the analytic method , In 39 PET studies from 22 healthy volunteers, 30 plasma samples were take n over 110 min. Results: The plasma integrals determined by the analytic an d numeric methods yielded a within-subject correlation coefficient of >0.95 and differences of <10%. Conclusion: Because the analytic method requires less blood sampling and does not require sampling immediately after radiotr acer injection, the experimental procedure is simplified without loss of ac curacy in CRRglc computation, and the effect of missing or incorrect sample s is reduced.