Abstract #0656

# What dominates the diffusivity time dependence transverse to axons: Intra- or extra-axonal water?

Hong-Hsi Lee1, Jelle Veraart1,2, Dmitry S. Novikov1, and Els Fieremans1

1New York University, Center for Biomedical Imaging, New York, NY, United States, 2iMinds-Vision Lab, University of Antwerp, Antwerp, Belgium

Diffusion MRI enables to evaluate microstructure at the mesoscopic scale. In particular, tuning the diffusion time over a wide range could increase the sensitivity for acquiring useful biomarkers, such as the axonal diameter or density. However, it is unclear whether either intra-, or extra-axonal water attribute most to the observed changes of diffusion signal with diffusion time. Here, we evaluate the dependence of the diffusion coefficient (obtained from the diffusion signal at low $$b$$$-value) on $$\delta$$$ and $$\Delta$$\$ in the direction perpendicular to axons in the human brain, and explain these dependencies by diffusion of water in the extra-axonal space.

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