MR diffusion tensor spectroscopy and imaging

Abstract

This paper describes a new NMR imaging modality--MR diffusion tensor imaging. It consists of estimating an effective diffusion tensor, Deff, within a voxel, and then displaying useful quantities derived from it. We show how the phenomenon of anisotropic diffusion of water (or metabolites) in anisotropic tissues, measured noninvasively by these NMR methods, is exploited to determine fiber tract orientation and mean particle displacements. Once Deff is estimated from a series of NMR pulsed-gradient, spin-echo experiments, a tissue's three orthotropic axes can be determined. They coincide with the eigenvectors of Deff, while the effective diffusivities along these orthotropic directions are the eigenvalues of Deff. Diffusion ellipsoids, constructed in each voxel from Deff, depict both these orthotropic axes and the mean diffusion distances in these directions. Moreover, the three scalar invariants of Deff, which are independent of the tissue's orientation in the laboratory frame of reference, reveal useful information about molecular mobility reflective of local microstructure and anatomy. Inherently tensors (like Deff) describing transport processes in anisotropic media contain new information within a macroscopic voxel that scalars (such as the apparent diffusivity, proton density, T1, and T2) do not.

Neurite dispersion: a new marker of multiple sclerosis spinal cord pathology?

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MR connectomics: Principles and challenges

“…Past and current state of the art Diffusion-weighted magnetic resonance imaging (MRI), received strong attention for the first time in the early 90s as it proved to be a sensitive biomarker for acute stroke (Moseley et al, 1990). The second reason diffusion imaging came to attention, was because it was observed that not only does white matter exhibit reliable anisotropic properties (Basser et al, 1994;Douek et al, 1991) but that it is indeed possible to infer fiber tract trajectories on the basis of these patterns (Conturo et al, 1999;Mori et al, 1999;Wedeen, 1996). Diffusion Tensor Imaging and tractography was born.…”

Efficient gradient calibration based on diffusion MRI

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