Abstract #1263

Predicting Mesoscopic Larmor Frequency Shifts with Diffusion MRI in Ex Vivo Pig Optic Nerve

Anders Dyhr Sandgaard¹, André Pampel², Roland Müller², Niklas Wallstein², Toralf Mildner², Aage Kristian Olsen Alstrup^3,4, Carsten Jäger^5,6, Harald E. Möller^2,7, and Sune Nørhøj Jespersen^1,8

¹Center of Functionally Integrative Neuroscience, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark, ²NMR Methods & Development Group, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, ³Department of Clinical Medicine, Aarhus University, Aarhus, Denmark, ⁴Department of Nuclear Medicine and PET, Aarhus University Hospital, Aarhus, Denmark, ⁵Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, ⁶Center of Neuropathology and Brain Research, Medical Faculty, University of Leipzig, Paul Flechsig Institute, Leipzig, Germany, ⁷Felix Bloch Institute for Solid State Physics, Leipzig University, Leipzig, Germany, ⁸Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark

Synopsis

Keywords: Susceptibility/QSM, Quantitative Susceptibility mapping

Motivation: Larmor frequency shifts in white matter (WM) depend on orientation due to anisotropic microstructure. Accurate magnetic susceptibility estimation in brain tissue requires a model for these sub-voxel shifts.

Goal(s): To validate if µQSM can predict measured WM Larmor frequency shifts by incorporating mesoscopic shifts from orientationally dispersed hollow cylinders and spherical inclusions.

Approach: We acquired dMRI and MGE images of a pig optic nerve in PBS at multiple orientations using a 3T Siemens Connectom scanner, comparing sub-voxel shifts to model predictions.

Results: µQSM successfully predicted tissue Larmor frequency, suggesting mesoscopic shifts from uniformly magnetized axons explain the observed changes, without invoking susceptibility anisotropy.

Impact: This study elucidates the nature of Larmor frequency shifts in coherent white matter, enhancing our understanding of its microstructural origin. These insights have the potential to improve QSM techniques by achieving better estimation of tissue magnetic susceptibility.

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