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ORIGINAL RESEARCH article

Front. Phys.
Sec. Medical Physics and Imaging
Volume 13 - 2025 | doi: 10.3389/fphy.2025.1516630

A diffusion MRI model for random walks confined on cylindrical surfaces: Towards non-invasive quantification of myelin sheath radius

Provisionally accepted
  • 1 Centre Hospitalier Universitaire Vaudois (CHUV), Lausanne, Vaud, Switzerland
  • 2 Center for Biomedical Imaging (CIBM), Lausanne, Vaud, Switzerland
  • 3 Swiss Federal Institute of Technology Lausanne, Lausanne, Vaud, Switzerland
  • 4 Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands, Netherlands
  • 5 Brain Research Imaging Center, School of Psychology, College of Biomedical and Life Sciences, Cardiff University, Cardiff, United Kingdom

The final, formatted version of the article will be published soon.

    Quantifying the myelin sheath radius of myelinated axons in vivo is important for understanding, diagnosing, and monitoring various neurological disorders. Despite advancements in diffusion MRI (dMRI) microstructure techniques, there are currently no models specifically designed to estimate myelin sheath radii. This proof-of-concept theoretical study presents two novel dMRI models that characterize the signal from water diffusion confined to cylindrical surfaces, approximating myelin water diffusion.We derive their spherical mean signals, eliminating fiber orientation and dispersion effects for convenience. These models are further extended to account for multiple concentric cylinders, mimicking the layered structure of myelin. Additionally, we introduce a method to convert histological distributions of axonal inner radii from the literature into myelin sheath radius distributions. We also derive analytical expressions to estimate the effective myelin sheath radius expected from these distributions. Monte Carlo (MC) simulations conducted in cylindrical and spiral geometries validate the models. These simulations demonstrate agreement with analytical predictions. Furthermore, we observe significant correlations between the effective radii derived from histological distributions and those obtained by fitting the dMRI signal to a single-cylinder model. These models may be integrated with existing multi-compartment dMRI techniques, opening the door to non-invasive in vivo assessments of myelin sheath radii. Such assessments would require MRI scanners equipped with strong diffusion gradients, allowing measurements with short echo times. Further work is required to validate the technique with real dMRI data and histological measurements.

    Keywords: diffusion MRI, Myelin water, Monte Carlo simulations, white matter microstructure, Myelin sheath radius

    Received: 24 Oct 2024; Accepted: 27 Jan 2025.

    Copyright: © 2025 Canales-Rodríguez, Tax, Fischi-Gomez, Jones, Thiran and Rafael-Patiño. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

    * Correspondence: Erick Jorge Canales-Rodríguez, Centre Hospitalier Universitaire Vaudois (CHUV), Lausanne, 1011, Vaud, Switzerland

    Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.