A revised model for estimating g-ratio from MRI

A key measure of white matter health is the g-ratio, which is defined as the ratio between the inner axon radius and the outer, myelinated, axon radius. Recent methods have been proposed to measure the g-ratio non-invasively using the relationship between two magnetic resonance imaging (MRI) measures. While this relationship is intuitive, it predicates on the simplifying assumption that g-ratio is constant across axons. Here, we extend the model to account for a distribution of g-ratio values within an imaging voxel, and evaluate this model with quantitative histology from normal and hypomyelinated mouse brains. •Revised model for MRI measure of g-ratio, accounting for distribution of g values•gMRI reports on axon-area-weighted measures of g-ratio•Validation with quantitative histology from control and hypomyelinated mice