Predicting Mesoscopic Larmor Frequency Shifts in White Matter with Diffusion MRI - A Monte-Carlo Study in Axonal Phantoms

Motivation: Axonal magnetic microstructure causes an anisotropic mesoscopic Larmor frequency shift in MRI that depends on each axon's direction relative to the B0 field. This shift is modeled in μQSM Goal(s): This study aims to validate μQSM's ability to predict mesoscopic Larmor frequency shifts using diffusion MRI (dMRI) data from realistic white matter axons. Approach: Monte-Carlo simulations in the intra-axonal space of mesoscale in-silico white matter axonal phantoms were performed to test whether fiber orientation distributions estimated from diffusion MRI can predict the anisotropic mesoscopic Larmor frequency shift induced by the axons. Results: dMRI successfully predicts mesoscopic Larmor frequency from in-silico white matter microstructure. Impact: μQSM may improve estimation of tissue magnetic susceptibility and lead to susceptibility imaging with higher diagnostic value.