High Angular Resolution Diffusion Imaging of the Human Brain

Introduction The use of a tensor to describe diffusion in anisotropic tissue such as white matter or cardiac muscle is predicated on the assumption of Gaussian diffusion (I, 2). The diffusion may, however, exhibit non-Gaussian behavior if the diffusion is restricted (3), or if there is slow exchange between partial volume components containing Gaussian diffusion. The 6 gradient direction sampling typical of standard tensor imaging experiments cannot resolve such spatially non-Gaussian diffusion, and thus higher angular resolution sampling is required. Here, we show that sampling the apparent diffusion coefficient at higher angular resolutions provides evidence for non-Gaussian diffusion in human brain white matter regions containing heterogeneous fiber orientations (4).