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

Abstract

Summary:The [IHF]fluorodeoxyglucose (FDG) scan method with positron emission computed tomography was used to determine patterns of local cere bral glucose utilization (LCMRg1u) 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 CMRglu was 26.1 ± 6. I /Lmol 100 g-l min-1 (mean ± SD, n = 40). At age 78, mean CMRglu 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 CMRglu 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 CMRglU of overall cortex, caudate, and thalamus was equal in individuals at all ages. The slopes of decline with age were similar when LCM Rglu was averaged over zones corresponding to centrum semiovale, caudate, putamen, and fron tal, temporal, parietal, occipital, and primary visual cortex. However, the met abolic 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. 163 koloff et aI., 1977) used in animals, but emission computed tomography is substituted for the au toradiography. After intravenous injection, FDG enters the brain, is phosphorylated by brain hexokinase, and the metabolic product, FDG-6-P0 4 , remains fixed with only slow dephosphoryla tion. The time course of specific activity is mea sured in plasma, brain activity is determined by scanning, and with knowledge of predetermined rate constants, an operational equation allows cal culations of LCMRglu that are distributed in a cross-

Computed Tomography and Positron Emission Transaxial Tomography Evaluations of Normal Aging and Alzheimer's Disease

“…(1983), show no relationship between age and spe cific metabolic rate of the surviving tissue. Our find ings do not agree with those of Kuhl et al (1982).…”

“…(1981) and Fieschi and Lenzi (1983) reported a trend of diminishing gray matter oxygen metabo lism with age only until the fIfth decade. Using PETT to study glucose metabolism, Kuhl et al (1982) found an age-dependent but variable decline in regional metabolic rates, but de Leon et aI. (1983), Ferris et aI.…”

Evolving Knowledge of Sex Differences in Brain Structure, Function, and Chemistry

“…Consistent with the findings of sex differences in cerebral blood flow, cerebral metabolic rate of glucose utilization (CMRglu) tends to be higher in women versus men (46), particularly in the orbital frontal area (47) although not consistently (48)(49)(50). However, global CMRglu may be inversely correlated with brain size such that individuals with smaller brains have higher CMRglu (48;51), effectively negating sex differences in metabolism.…”

Cerebral Glucose Metabolism as a Function of Age in Man: Influence of the Rate Constants in the Fluorodeoxyglucose Method

“…Kuhl et aL (1982) made similar observations with positron tomogra phy and the FDG method. We evaluated the rate constants in order to determine whether the ob served decline in metabolism actually reflects a change in rate constants and to search for any selective alteration in the transport or phosphoryla tion processes as a function of age.…”