Besides the voxel-by-voxel volumetric comparisons, as it is done in VBM methods [29, 30], diffusion tensor imaging (DTI) can be used to determine the directionality of the diffusion of hydrogen protons, which is assumed to provide information about the microstructural integrity of the fiber tracts [31, 32]. Although volumetric and diffusion-based methods measure different features of WM, both provide information on WM changes in patient groups compared to healthy controls, and meta-analytically integrating results of studies applying one of both methods can give a more comprehensive overview of the affected brain regions (e.g., [33]).
