Anisotropy in high-resolution diffusion-weighted MRI and anomalous diffusion

► Arbitrary anisotropic diffusion can be modeled by space-fractional diffusion. ► A generalization of the Stejskal-Tanner formula is derived for anisotropic MRI. ► This generalization explains deviations from the classical Stejskal-Tanner formula. ► Our model yields several fiber tract directions in a voxel and allows for crossings. ► The Stejskal-Tanner formula for a time-fractional model is also derived.