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Abstract #0650

Exploring the effect of varying axonal shape on the transverse diffusion inside EM-reconstructed axons using 3d Monte Carlo simulations

Hong Hsi Lee1,2, Els Fieremans1,2, and Dmitry S Novikov1,2

1Center for Biomedical Imaging, New York University School of Medicine, New York, NY, United States, 2Center for Advanced Imaging Innovation and Research (CAI2R), New York University School of Medicine, New York, NY, United States

Diffusion inside axons is restricted and thus non-Gaussian, with diffusion MRI (dMRI) signal strongly sensitive to the shape of the confining axon. This sensitivity is confounded by the coarse-graining of the diameter/shape variation along the fiber during the diffusion time. Here, we analytically relate dMRI metrics to the axonal shape, and validate our theory using 3d Monte-Carlo simulations in beaded cylinders and realistic axons reconstructed from electron microscopy images of the mouse brain white matter. Our simulation results show that the intra-axonal space has a non-trivial kurtosis transverse to axons. Its value is different from that in a perfectly straight cylinder, and needs to be considered in axonal diameter measurements (e.g., spinal cord, strong gradients, intra-axonal metabolites).

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