Keywords: Diffusion Modeling, Diffusion Modeling, Peripheral Nervous System (PNS), Intra-axonal fraction, Diffusion-weighted MRI
Motivation: The “stick”, a standard zero-radius diffusion model, can bias intra-axonal fraction (fa) estimation when large axons (e.g., radii ≥ 4 µm) are present, as in the peripheral nervous system (PNS).
Goal(s): To compare signal models for in vivo fa characterization in the PNS: Ball-and-Stick (BS), Two-Axon Population (TAP) and general Gamma Distribution Axon Population (GDAP).
Approach: Maps of fa and other diffusion properties were compared in healthy and diseased (Multiple Sclerosis) sciatic nerves in vivo through BS, TAP and GDAP.
Results: TAP and GDAP models provided higher estimates of fa than BS and may thus offer promising new PNS biomarkers.
Impact: We demonstrate that diffusion MRI can accurately resolve axon diameter information in the sciatic nerve in vivo using Two-Axon Population (TAP) and Gamma Distribution Axon Population (GDAP) imaging. These methods provide higher intra-axonal signal fraction estimates than the Ball-and-Stick model
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