Axon diameter mapping is confounded by glial cells

The specificity of strongly diffusion-weighted MRI to intra-axonal signal contributions to neuronal processes has always been presumed. Here we demonstrate empirically that strongly diffusion-weighted MRI data is also sensitive to a distinct isotropic compartment that may bias axon diameter estimates. We hypothesize that such a compartment represents isotropically-distributed glial processes. We use in vivo human data and Monte Carlo simulations to support our hypothesis and evaluate a novel strategy to suppress signal arising from glial cell bodies and processes to promote more accurate axon diameter mapping.