Changes in the Heterogeneity of Cerebral Glucose Metabolism with Healthy Aging: Quantitative Assessment by Fractal Analysis

Abstract

ABSTRACT Background and Purpose. It has been shown that heterogeneity of cerebral glucose metabolism is increased in neuropsychiatric degenerative diseases. However, proper assessment of older patients requires knowledge about the effect of aging on hetero geneity. This study characterized the effects of aging on the heterogeneity of the distribution of cerebral glucose metabolism in healthy volunteers. Methods. Sixty‐six healthy volunteers (age range, 19–75 years) underwent flurodeoxyglucose brain positron emission tomography (PET), and all the PET images were spatially normalized onto a previously segmented standard brain template to parcel the brain regions automatically. Fractal dimension was regarded as a quantitative measurement for the heterogeneity of cerebral glucose metabolism and obtained for 9 brain regions. Participants were subdivided into young/midlife and elderly groups, and the Student t test was applied to the comparison of fractal dimensions in those groups. Analysis of covariance was performed for each region to explore the effects of age, gender, age‐by‐gender interaction, and total counts in the brain on the observed metabolic heterogeneity. Results. Fractal dimensions were higher for elderly volunteers in most brain regions. Differences between the 2 groups in fractal dimension emerged within the whole gray matter, temporal lobe, striatum, and cingulate. No significant gender differences, age‐by‐gender interactions, or total counts were observed. Significant age effects were observed in the whole gray matter, frontal lobe, temporal lobe, striatum, and cingulate gyrus. Con clusions. Heterogeneity in the cerebral glucose metabolism of healthy volunteers increased with age, and individual variations of heterogeneity were higher in older volunteers. However, there was no significant difference between male and female volunteers of the same age. The effect of age on heterogeneity was not regionally uniform.