title: In vivo observation and biophysical interpretation of time-dependent diffusion in human white matter.
abstract: The presence of micrometer-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 μm. 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.
authors.affiliation: Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY 10016, USA. Electronic address: els.fieremans@nyumc.org.
authors.forename: Els
authors.initials: E
authors.lastname: Fieremans
authors.affiliation: Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY 10016, USA.
authors.forename: Lauren M
authors.initials: LM
authors.lastname: Burcaw
authors.affiliation: Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY 10016, USA.
authors.forename: Hong-Hsi
authors.initials: HH
authors.lastname: Lee
authors.affiliation: Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY 10016, USA.
authors.forename: Gregory
authors.initials: G
authors.lastname: Lemberskiy
authors.affiliation: Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY 10016, USA; iMinds Vision Lab, Department of Physics, University of Antwerp, Antwerp, Belgium.
authors.forename: Jelle
authors.initials: J
authors.lastname: Veraart
authors.affiliation: Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY 10016, USA.
authors.forename: Dmitry S
authors.initials: DS
authors.lastname: Novikov
mesh_terms: D000328:Adult; D001921:Brain / Q000648:ultrastructure*; D001931:Brain Mapping / Q000379:methods*; D056324:Diffusion Tensor Imaging; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D066127:White Matter / Q000648:ultrastructure
keywords: Diffusion MRI; Diffusion tensor imaging; Hindered diffusion; STEAM sequence; Time-dependent diffusion; White matter