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Abstract #4043

MyCaliber: Axon diameter mapping from myelin water diffusion -- Theory, Resolution Limit, and Monte Carlo simulations

Hong Hsi Lee1,2, Dmitry S Novikov3,4, Els Fieremans3,4, and Susie Y Huang1,2
1Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States, 2Harvard Medical School, Boston, MA, United States, 3Center for Advanced Imaging Innovation and Research, New York, NY, United States, 4Radiology, New York University School of Medicine, New York, NY, United States

Synopsis

Keywords: Simulation/Validation, Simulation/Validation, Myelin water, axon diameter, diffusion

Motivation: Probing diffusion in myelin water using diffusion-weighted T1-/T2-selective MRI acquisitions enables to non-invasively measure myelinated axon radius. Its application for in vivo measurements requires validation through diffusion simulations.

Goal(s): To propose the theory of myelin water diffusion in wide-gradient-pulse sequence and validate its applicability to axon radius estimation via Monte Carlo simulations.

Approach: We derived the theory using Gaussian-phase-approximation. We validated the proposed model by performing diffusion simulations in infinitely thin cylindrical surfaces or concentric cylindrical layers of finite thickness.

Results: Simulation results validated the theory of myelin water diffusivity and axon radius estimation using spherical-mean signals.

Impact: Measuring restricted diffusion of myelin water in-between myelin sheaths using diffusion MRI enables to in vivo measure axon radius. Simulation results demonstrated its applicability at SNR≥5 on Connectome 2.0 scanner. The protocol can be adapted for clinically available high-gradient-performance scanners.

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Keywords