A new method for mapping diffusivity profiles in tissue is presented. The Bloch-Torrey equation is modified to include a diffusion term with an arbitrary rank Cartesian tensor. This equation is solved to give the expression for the generalized Stejskal-Tanner formula quantifying diffusive attenuation in complicated geometries. This makes it possible to calculate the components of higher-rank te...

INTRODUCTION: To remove noise artifacts and enhance SNR, diffusion-weighted (DW) measurements are often repeated multiple times (NEX) along each gradient direction (typically, from 2 to 4 measurements) and each DW image is averaged. This averaging increases acquisition time considerably. It is also not clear what effects it has on the reconstructed diffusion profiles such as the orientation dis...

Introduction While the standard diffusion tensor imaging (DTI) approach has proven to be a valuable tool in detecting local tissue structure and reconstructing neural fiber networks in brain, it cannot accurately reveal the white matter structure in the presence of multiple fiber orientations within a single voxel. In particular, for crossed fibers, the second-order diffusion tensor model fails...

We denoise HARDI (High Angular Resolution Diffusion Imaging) data arising in medical imaging. Diffusion imaging is a relatively new and powerful method to measure the 3D profile of water diffusion at each point. This can be used to reconstruct fiber directions and pathways in the living brain, providing detailed maps of fiber integrity and connectivity. HARDI is a powerful new extension of diff...

Q-ball imaging (QBI) is a high angular resolution diffusion imaging (HARDI) technique which has been proven very successful in resolving multiple intravoxel fiber orientations in MR images. The standard computation of the orientation distribution function (ODF, the probability of diffusion in a given direction) from q-ball uses linear radial projection, neglecting the change in the volume eleme...

Target Audience: MR physicists and brain researchers with an interest for novel diffusion-imaging schemes. Purpose: High Angular Resolution Diffusion Imaging (HARDI) is a diffusion encoding scheme for resolving intra-voxel fiber structures and crossings. It typically involves acquiring as many as a few hundred diffusion weighted images using a single-shot EPI sequence. The main factors limiting...

Diffusion MRI (dMRI) provides the ability to reconstruct neuronal fibers in the brain, in vivo, by measuring water diffusion along angular gradient directions in q-space. High angular resolution diffusion imaging (HARDI) can produce better estimates of fiber orientation than the popularly used diffusion tensor imaging, but the high number of samples needed to estimate diffusivity requires lengt...

High angular resolution diffusion imaging (HARDI) is a powerful variant of diffusion MRI, which images the 3D profile of diffusion at each imaged location in the brain. At each voxel, this leads to an orientation density function (ODF) expressing the probability density of water diffusion in each direction on the unit sphere. As diffusion is greatest along the brain’s axons, these functions are...

BACKGROUND The most frequently used method for fiber tractography based on diffusion tensor imaging (DTI) is associated with restrictions in the resolution of crossing or kissing fibers and in the vicinity of tumor or edema. Tractography based on high-angular-resolution diffusion imaging (HARDI) is capable of overcoming this restriction. With compressed sensing (CS) techniques, HARDI acquisitio...

BACKGROUND A number of imaging factors can affect the orientation distribution function (ODF) reconstruction in high angular resolution diffusion imaging (HARDI). The aim of this study was to investigate the effect of the b-value on the HARDI reconstruction and to seek for the appropriate b-value for ODF reconstruction from clinical HARDI data. METHODS Diffusion MRI data with various b-values...