Abstract: A method for quantitatively assessing diffusion anisotropy according to an invariant anisotropy index that accounts for orientational coherence of the measured principal directions between different localized regions of an object to counteract the bias and increased variance effects of noise inherent in the diffusion measurement. A diffusion weighted imaging sequence is performed on a two-dimensional slice of an object to provide raw diffusion weighted image signals, which are processed by conventional Fourier transform and magnitude reconstruction to provide diffusion weighted images, from which a diffusion tensor is estimated for each voxel of the imaged slice. In each voxel a lattice anisotropy index is calculated as a function of both the eigenvalues and eigenvectors of neighboring voxels such that intervoxel orientational coherence compensates noise-induced bias effects. The orientational coherence measure between two voxels is calculated according to an intervoxel deviatoric tensor dot product.