Positron Emission Tomographic Studies of Local Cerebral Glucose Metabolism in Humans in Physiological and Pathophysiological Conditions

Abstract

This chapter discusses the positron emission tomographic studies of local cerebral glucose metabolism in humans in physiological and pathophysiological conditions. Glucose utilization is stoichiometrically related to oxygen consumption in the aerobic state, except in a few situations such as starvation and insulin hypoglycemia, and provides a measure of energy metabolism in the anaerobic state as well. The ability to detect alterations in local cerebral metabolism in man has become a valuable tool in advancing our understanding of disorders affecting the brain, many of which are focal in nature. In order to determine the regional metabolic rate for glucose, one must measure, the distribution of the 18 F activity in the brain, the time course of arterial plasma ‘ 18 F’fluorodeoxyglucose (‘ 18 F’FDG) and glucose concentrations, and know the values of the rate constants and lumped constant for FDG in humans. The three-dimensional distribution of 18 F activity in the brain is determined with a positron emission tomographic scanner. Such an instrument consists of an array of scintillation detectors positioned around the subject's head. The detectors are mounted on a gantry capable of rectilinear and/or rotatory motion. From the measured data, transverse sections through the brain are calculated using a filtered, back-projection reconstruction technique.