Frontiers in Neuroscience (Nov 2015)

Whole-brain in-vivo measurements of the axonal g-ratio in a group of 37 healthy volunteers

  • Siawoosh eMohammadi,
  • Siawoosh eMohammadi,
  • Daniel eCarey,
  • Fred eDick,
  • Joern eDiedrichsen,
  • Martin I Sereno,
  • Marco eReisert,
  • Martina F Callaghan,
  • Nikolaus eWeiskopf,
  • Nikolaus eWeiskopf

DOI
https://doi.org/10.3389/fnins.2015.00441
Journal volume & issue
Vol. 9

Abstract

Read online

The g-ratio, quantifying the ratio between the inner and outer diameters of a fiber, is an important microstructural characteristic of fiber pathways and is functionally related to conduction velocity. We introduce a novel method for estimating the MR g-ratio non-invasively across the whole brain using high-fidelity magnetization transfer (MT) imaging and single-shell diffusion MRI. These methods enabled us to map the MR g-ratio in vivo across the brain’s prominent fiber pathways in a group of 37 healthy volunteers and to estimate the inter-subject variability. Effective correction of susceptibility-related distortion artifacts was essential before combining the MT and diffusion data, in order to reduce partial volume and edge artifacts. The MR g-ratio is in good qualitative agreement with histological findings despite the different resolution and spatial coverage of MRI and histology. The MR g-ratio holds promise as an important non-invasive biomarker due to its microstructural and functional relevance in neurodegeneration.

Keywords