“…HARDI methods attempt to recover more information about the angular structure of intravoxel diffusion by acquiring larger numbers of diffusion-encoding directional measurements at higher diffusionweighting factors (b values) than is routine for DTI [6][7][8]. There has been a growing list of proposed techniques for reconstructing fiber orientations from HARDI data, including spherical harmonic modeling of the apparent diffusion coefficient (ADC) profile [7,8], multitensor modeling [9], generalized tensor representations [10,11], persistent angular structure [12], circular spectrum mapping [13], q-ball imaging [14,15], spherical deconvolution [16], fiber orientation estimated on continuous axially symmetric tensors [17] and the diffusion orientation transform [18]. However, all of these HARDI approaches remain SNR-limited even on 3T scanners with parallel imaging capability, because of the need for both high spatial resolution and very strong diffusion-weighting, resulting in long examination times and/or suboptimal discrimination of intravoxel crossing fiber tracts.…”