Research has traditionally employed voxel-based morphometry (VBM) to estimate GM, WM, and cerebrospinal fluid (CSF) volumes on the voxel (millimeter) scale, whereas several scalar invariants derived from DTI, such as fractional anisotropy (FA) and mean diffusivity (MD), have been used to characterize WM microarchitecture (Alcauter et al., 2011, Belke et al., 2015, Kim et al., 2015). Reduction in GM volume in mature adults often reflects hypotrophy due to cellular loss and may be responsible for associated behavioral impairments (De Bellis et al., 2000, Kroenke et al., 2014, Treit et al., 2013) whereas lower FA is often interpreted as lower integrity of the WM, which may reflect factors including axonal count and density, degree of myelination, and fiber organization (Alcauter et al., 2011, Belke et al., 2015, Kim et al., 2015, Steinbrink et al., 2008). Recent studies have also reported changes in DTI characteristics of cortical and subcortical GM regions, pointing to various structural and physiological mechanisms to explain the findings (Camara et al., 2007, Chanraud et al., 2009, Douaud et al., 2009, Hasan et al., 2009, Lebel et al., 2008,
