Abstract #0843

Origin of the time dependence of the diffusion-weighted signal in spinal cord white matter

Francesco Grussu¹, Andrada Ianuş^2,3, Carmen Tur¹, Ferran Prados^1,4, Torben Schneider^1,5, Sébastien Ourselin⁴, Ivana Drobnjak², Hui Zhang², Daniel C. Alexander², and Claudia A. M. Gandini Wheeler-Kingshott^1,6,7

¹UCL Institute of Neurology, Queen Square MS Centre, University College London, London, United Kingdom, ²Centre for Medical Image Computing, Department of Computer Science, University College London, London, United Kingdom, ³Champalimaud Centre for the Unknown, Champalimaud Foundation, Lisbon, Portugal, ⁴Translational Imaging Group, Centre for Medical Image Computing, Department of Medical Physics and Biomedical Engineering, University College London, London, United Kingdom, ⁵Philips UK, Guildford, Surrey, United Kingdom, ⁶Department of Brain and Behavioural Sciences, University of Pavia, Pavia, Italy, ⁷Brain MRI 3T Mondino Research Center, C. Mondino National Neurological Institute, Pavia, Italy

Time dependence of the brain white matter diffusion-weighted signal originates from both intra-axonal and extra-axonal spaces. Here, we investigate which of these contributions dominates in spinal cord white matter for clinically feasible acquisitions, to inform accurate model-based microstructural imaging. We analyse data from Monte Carlo simulations and from in vivo scans, and find that for diffusion times of 20-70 ms time dependence has mostly intra-axonal origin. Such a time dependence influences the estimation of axonal volume fraction and extra-axonal diffusivity, and highlights the importance of using long diffusion times to support stick-like models for axons in the spinal cord.

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