DTI relies on thermally driven random motion of water molecules also known as Bronwian mo-tion, to supply tissue micro structural information in vivo (Le Bihan et al., 1986; Chenevert et al., 1990). In un constrained water molecules in a pure liquid environment free of impediments dif-fusion is equal in all directions. The situation is referred to as 'isotropic'. In brain tissue, however, water diffusion is considerably reduced due to numerous barriers such as myelin sheaths, cell membranes, and white matter tracts. Diffusion of the water molecules is less restricted along the long-axis of a group of aligned tissue fibers than perpendicular to it. The condition of directionally-dependant diffusion referred to as 'anisotropic'. |
