Here, we employ diffusion tensor imaging (DTI), a non-invasive technique for discerning microstructural white matter integrity in vivo. This technique is sensitive to variations in random motions, or diffusion, of water in neural tissues. In highly oriented and coherent brain tissue such as white matter fiber tracts, diffusion is anisotropic and greater along rather than perpendicular to axonal fibers (Le Bihan et al., 2001). Through acquisition of multiple images along different directions, one can quantify the directional dependence of diffusion and, from this, infer structural characteristics of the local tissue environment. Two primary scalar measures can be derived from DTI data: 1) fractional anisotropy (FA), a measurement of the directional variance of diffusional motion and 2) mean diffusivity (MD), measuring the overall magnitude of diffusional motion within a given voxel (Moritani et al., 2005). These measures index relationships between signal intensity changes and underlying structure, and are used in tandem to assess white matter quality (Conturo et al., 1999; Pierpaoli and Basser, 1996; Shimony et al., 1999).
