Journal
NEUROIMAGE
Volume 129, Issue -, Pages 414-427Publisher
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
- Raymond and Beverly Sackler Laboratories for Convergence of Physical, Engineering, and Biomedical Sciences
- Litwin Foundation
- National Institute of Neurological Disorders and Stroke of the National Institutes of Health [R01NS088040]
- 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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