Susceptibility-induced internal gradients reveal axon morphology and cause anisotropic effects in the dMRI signal

Winther, S.; Lundell, H.; Rafael-Patino, J.; Andersson, M.; Thiran, J.-P.; Dyrby, T. B.

doi:10.1101/2023.05.01.538981

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bioRxiv · 10.1101/2023.05.01.538981

Susceptibility-induced internal gradients reveal axon morphology and cause anisotropic effects in the dMRI signal

Winther, S.·Lundell, H.·Rafael-Patino, J.·Andersson, M.·Thiran, J.-P.·Dyrby, T. B.

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Abstract

Diffusion-weighted MRI is our most promising method for estimating microscopic tissue morphology in vivo. The signal acquisition is based on scanner-generated external magnetic gradients. However, it will also be affected by susceptibility-induced internal magnetic gradients caused by interaction between the tissue and the static magnetic field of the scanner. With 3D in silico experiments, we show how internal gradients cause morphology-, compartment-, and orientation-dependence of spin-echo and pulsed-gradient spin-echo experiments in myelinated axons. These effects are unseen in previous 2D modelling. For an ex vivo monkey brain, we observe the orientation-dependency generated only when including non-circular cross-sections in the in silico morphological configurations, and find orientation-dependent deviation of up to 17% for diffusion tensor metrics. Our findings underline the importance of accounting for realistic 3D axon morphology in modelling. Interestingly, the morphology-specific orientation-dependency trends show potential for a novel sensitivity to morphology, which is not attainable by the theoretical diffusion-weighted MRI signal itself.

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Winther, S., Lundell, H., Rafael-Patino, J., Andersson, M., Thiran, J.-P., Dyrby, T. B.. 2023-05-02. Susceptibility-induced internal gradients reveal axon morphology and cause anisotropic effects in the dMRI signal. https://doi.org/10.1101/2023.05.01.538981

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