An important consideration in brain imaging, it refers to the ability of water molecules to move more in certain directions than in others. When water is freely diffusing, it has no directionality (i.e., it is isotropic). In ordered structures such as the cerebral cortex, however, this tendency is most often dependent on, or preferentially restricted to, the long axes or orientations of white matter fiber tracts in the surrounding water (i.e., it is anisotropic). There is a higher anisotropy in white matter compared to gray matter, as well as in adult brains compared to those of newborns. Consequently, diffusion anisotropy, among other things, can provide an indication of abnormalities in myelination.
See Brain (neuro-) imaging, Diffusion tensor imaging, Gray matter, Myelin, Human Connectome Project (HCP), Myelination, White matter