Axon radius measurements in vivo from diffusion MRI: a feasibility study

This paper investigates the feasibility of using diffusion MRI to measure axon-cell dimensions in the white matter of live subjects. A simple geometric model of white-matter tissue provides an expression that relates the axon radius to the diffusion MRI signal. The aim is to determine the accuracy and precision with which we can estimate this potentially important new biomarker. Precision and accuracy depend critically on the acquisition protocol. The paper proposes a general strategy to optimize the experiment design of in-vivo diffusion MRI experiments. The applicability of the design optimization extends well beyond the current work to optimizing the acquisition for any model of the diffusion process. Simulation experiments and results suggest feasibility of measuring larger axon radii in vivo on modern MRI scanners using the optimized acquisition schemes, but that higher gradient strengths are required to measure smaller axons.