GM, WM, and CSF were segmented with the 3DVIEWNIX software system (21) by analyzing both proton density – and T2-weighted images. The process began with segmentation of the intracranial brain (GM, WM, and CSF) by using the theory of fuzzy connectedness (22). All segmented brain volume images (more than 50 sections in each subject’s brain) were individually reviewed, and an expe-rienced neuroradiologist (Y.G.) excluded any residual ex-tracranial components, if needed. GM, WM, and CSF were each identified as individual three-dimensional fuzzy con-nected objects (Fig 1) according to their “affinity,”“fuzzy adjacency,” and “hanging togetherness” (22). This technique created a volume image by using thin-section dual-echo proton density– and T2-weighted images for GM, WM, and CSF from all sections that covered the whole brain. In repeated studies,the coefficient of variation was shown to be 2.1% for the GM volume, 1.9% for the WM volume, and 1.5% for the CSF volume. To normalize for head size variability, the %GM volume and %WM volume were computed as the percentage of the intracranial volume
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