Whole-brain in-vivo measurements of the Axonal G-Ratio in a group of 37 healthy volunteers

Mohammadi, S. and Carey, Daniel and Dick, F and Diedrichsen, J. and Sereno, Martin I. and Reisert, M. and Callaghan, M.F. and Weiskopf, N. (2015) Whole-brain in-vivo measurements of the Axonal G-Ratio in a group of 37 healthy volunteers. Frontiers in Neuroscience 9 , ISSN 1662-453X.

Abstract

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.

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