4.7 Article

In vivo observation and biophysical interpretation of time-dependent diffusion in human white matter

Journal

NEUROIMAGE
Volume 129, Issue -, Pages 414-427

Publisher

ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.neuroimage.2016.01.018

Keywords

Diffusion MRI; Diffusion tensor imaging; STEAM sequence; Time-dependent diffusion; Hindered diffusion; White matter

Funding

  1. Raymond and Beverly Sackler Laboratories for Convergence of Physical, Engineering, and Biomedical Sciences
  2. Litwin Foundation
  3. National Institute of Neurological Disorders and Stroke of the National Institutes of Health [R01NS088040]
  4. Fund for Scientific Research-Flanders [12S1615N]

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The presence ofmicrometer-level restrictions leads to a decrease of diffusion coefficient with diffusion time. Here we investigate this effect in human white matter in vivo. We focus on a broad range of diffusion times, up to 600 ms, covering diffusion length scales up to about 30 mu m. We perform stimulated echo diffusion tensor imaging on 5 healthy volunteers and observe a relatively weak time-dependence in diffusion transverse to major fiber tracts. Remarkably, we also find notable time-dependence in the longitudinal direction. Comparing models of diffusion in ordered, confined and disordered media, we argue that the time-dependence in both directions can arise due to structural disorder, such as axonal beads in the longitudinal direction, and the random packing geometry of fibers within a bundle in the transverse direction. These time-dependent effects extend beyond a simple picture of Gaussian compartments, and may lead to novel markers that are specific to neuronal fiber geometry at the micrometer scale. (C) 2016 Elsevier Inc. All rights reserved.

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