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Multi-parametric quantitative MRI reveals three different white matter subtypes

by Jack R. Foucher, Olivier Mainberger, Julien Lamy, Mathieu D. Santin, Alexandre Vignaud, Mathilde M. Roser, Paulo L. de Sousa

Introduction

Magnetic resonance imaging (MRI) shows slight spatial variations in brain white matter (WM). We used quantitative multi-parametric MRI to evaluate in what respect these inhomogeneities could correspond to WM subtypes with specific characteristics and spatial distribution.

Materials and methods

Twenty-six controls (12 women, 38 ±9 Y) took part in a 60-min session on a 3T scanner measuring 7 parameters: R1 and R2, diffusion tensor imaging which allowed to measure Axial and Radial Diffusivity (AD, RD), magnetization transfer imaging which enabled to compute the Macromolecular Proton Fraction (MPF), and a susceptibility-weighted sequence which permitted to quantify R2* and magnetic susceptibility (χm). Spatial independent component analysis was used to identify WM subtypes with specific combination of quantitative parameters values.

Results

Three subtypes could be identified. t-WM (track) mostly mapped on well-formed projection and commissural tracts and came with high AD values (all p < 10−18). The two other subtypes were located in subcortical WM and overlapped with association fibers: f-WM (frontal) was mostly anterior in the frontal lobe whereas c-WM (central) was underneath the central cortex. f-WM and c-WM had higher MPF values, indicating a higher myelin content (all p < 1.7 10−6). This was compatible with their larger χm and R2, as iron is essentially stored in oligodendrocytes (all p < 0.01). Although R1 essentially showed the same, its higher value in t-WM relative to c-WM might be related to its higher cholesterol concentration.

Conclusions

Thus, f- and c-WMs were less structured, but more myelinated and probably more metabolically active regarding to their iron content than WM related to fasciculi (t-WM). As known WM bundles passed though different WM subtypes, myelination might not be uniform along the axons but rather follow a spatially consistent regional variability. Future studies might examine the reproducibility of this decomposition and how development and pathology differently affect each subtype.

Authors:   Jack R. Foucher; Olivier Mainberger; Julien Lamy; Mathieu D. Santin; Alexandre Vignaud; Mathilde M. Roser; Paulo L. de Sousa
Journal:   PLoS ONE
Volume:   13
edition:   6
Year:   2018
Pages:   e0196297
DOI:   10.1371/journal.pone.0196297
Publication date:   15-Jun-2018
Facts, background information, dossiers
  • white matter
  • iron
  • reproducibility
  • Proton
  • pathology
  • oligodendrocytes
  • myelination
  • myelin
  • magnetization
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