Effects of Human Aging on Patterns of Local Cerebral Glucose Utilization Determined by the [18F] Fluorodeoxyglucose Method

Abstract

The [¹⁸F]fluorodeoxyglucose (FDG) scan method with positron emission computed tomography was used to determine patterns of local cerebral glucose utilization (LCMR_glu) in 40 normal volunteer subjects aged 18 to 78 years. Throughout all the studies, each subject was quiet, without movement, with eyes open and ears unplugged, exposed only to ambient room light and sound. For the entire group, whole brain mean CMR_glu was 26.1 ± 6.1 μmol 100 g⁻¹ min⁻¹ (mean ± SD, n = 40). At age 78, mean CMR glu was, on the average, 26% less than at age 18, an alteration of the same order as the variance among subjects at any age. The gradual decline of mean CMR_glu with advancing age occurred at a faster rate than was reported for mean cerebral oxygen utilization, possibly due to increasingly altered pathways for glucose utilization, or to increasing oxidation of ketone bodies or other alternative substrates. Glucose utilization in the hemispheres was symmetrical and mean CMR_glu of overall cortex, caudate, and thalamus was equal in individuals at all ages. The slopes of decline with age were similar when LCMR_glu was averaged over zones corresponding to centrum semiovale, caudate, putamen, and frontal, temporal, parietal, occipital, and primary visual cortex. However, the metabolic ratio of superior frontal cortex to superior parietal cortex declined with age, possibly due to selective degeneration of superior frontal cortex or to differences between age groups in the sensory and cognitive response to the study. These results should be useful in distinguishing age from disease effects when the FDG scan method is used.