Voxel-based morphometry - The methods

At its simplest, voxel-based morphometry (VBM) involves a voxel-wise compar ison of the local concentration of gray matter between two groups of subjec ts. The procedure is relatively straightforward and involves spatially norm alizing high-resolution images from all the subjects in the study into the same stereotactic space. This is followed by segmenting the gray matter fro m the spatially normalized images and smoothing the gray-matter segments. V oxel-wise parametric statistical tests which compare the smoothed gray-matt er images from the two groups are performed. Corrections for multiple compa risons are made using the theory of Gaussian random fields. This paper desc ribes the steps involved in VBM, with particular emphasis on segmenting gra y matter from MR images with nonuniformity artifact. We provide evaluations of the assumptions that underpin the method, including the accuracy of the segmentation and the assumptions made about the statistical distribution o f the data. (C) 2000 Academic Press.