PHYSIOLOGY

Changes in heterogeneity of cerebral glucose metabolism with healthy aging: quantitative assessment by fractal analysis

Jae Sung Lee*?, Sungil Cho*, Dong Soo Lee*, Kwang Suk Park*?, June-Key Chung*, Myung Chul Lee*

*Department of Nuclear Medicine, Seoul National University College of Medicine

TDepartment of Biomedical Engineering, Seoul National University College of Medicine

Introduction

It has been shown that heterogeneity of cerebral glucose metabolism increased in neuropsychiatric degenerative diseases, such as Alzheimer’s disease. However, proper assessment of old patients requires knowledge about the effect of aging on heterogeneity. The purpose of this study was to characterize the effects of aging on the heterogeneity of cerebral glucose metabolism distribution in healthy volunteers by 3D fractal analysis of F-18-FIX brain PET.

Methods

Forty normal volunteers with a mean age of 45.4221.4 y (age range: 19-75 y, M/F = 24/16) underwent F-IS-FDG brain PET. Exclusion criteria were lifetime history of any neurological, psychiatric or significant medical illnesses and past history of substance abuse. AlI the images were spatially normalized on previously segmented standard templates to parcel entire cerebral cortex into 4 volumes of interest (VOI: frontal, parietal, temporal, and occipital lobes). Fractal dimension was regarded as a quantitative measurement for the heterogeneity of cerebral glucose metabolism, and fractal dimension for entire cerebral cortex and each VOI was obtained. Using 5 cutoff levels (35,40,45,50, and 55 % of the maximal voxel value), we obtained total number of voxels above each cutoff level, and calculated fractal dimension by relating the logarithms of cutoff level and number of voxels. Linear regression analysis was used to relate the fractal dimension for entire cerebral cortex and each VOI to age.

Results

For entire cerebral cortex, mean fractal dimension over all volunteers was 0.60+0.31. Glucose metabolism was more heterogeneous in temporal lobe (mean fractal dimension = 1.09+0.48) than the other areas (frontal: 0.4220.30, parietal: 0.35t0.31, occipital: 0.3820.23). There was a trend that fractal dimensions increased with age. However, their correlation was moderate and statistically significant only in the frontal lobe (r=O.43, p<O.Ol). Increase of fractal dimension per year was 0.0032, 0.0061, 0.0015, 0.0060, and 0.0003 for entire cerebral cortex and frontal, parietal, temporal, and occipital lobe, respectively.

Conclusion

We could find that heterogeneity of cerebral glucose metabolism increases according to the advancing age, and the effect of age on heterogeneity was not regionally uniform.

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