High angular resolution diffusion imaging reveals intravoxel white matter fiber heterogeneity

TLDR

DTI can resolve white‑matter fiber orientation when fibers are strongly aligned, but a voxel may contain a distribution of orientations due to crossing fibers. The study tested whether a geodesic, high‑b value diffusion gradient sampling scheme could resolve multiple fiber orientations within a single voxel. Because the diffusion signal was multimodal, the authors modeled it as a discrete mixture of Gaussian diffusion processes in slow exchange and solved for the underlying mixture of tensors using a gradient‑descent scheme. The multimodal diffusion signal revealed multiple intravoxel fiber orientations, and the multitensor reconstruction successfully resolved these populations in accordance with known white‑matter anatomy. Published in Magn Reson Med 48:577–582 (2002); © 2002 Wiley‑Liss, Inc.

Abstract

Abstract Magnetic resonance (MR) diffusion tensor imaging (DTI) can resolve the white matter fiber orientation within a voxel provided that the fibers are strongly aligned. However, a given voxel may contain a distribution of fiber orientations due to, for example, intravoxel fiber crossing. The present study sought to test whether a geodesic, high b‐ value diffusion gradient sampling scheme could resolve multiple fiber orientations within a single voxel. In regions of fiber crossing the diffusion signal exhibited multiple local maxima/minima as a function of diffusion gradient orientation, indicating the presence of multiple intravoxel fiber orientations. The multimodality of the observed diffusion signal precluded the standard tensor reconstruction, so instead the diffusion signal was modeled as arising from a discrete mixture of Gaussian diffusion processes in slow exchange, and the underlying mixture of tensors was solved for using a gradient descent scheme. The multitensor reconstruction resolved multiple intravoxel fiber populations corresponding to known fiber anatomy. Magn Reson Med 48:577–582, 2002. © 2002 Wiley‐Liss, Inc.