Larmor frequency shift from magnetized cylinders with arbitrary orientation distribution

TL;DR

This paper develops a theoretical model to predict the Larmor frequency shift in NMR and MRI caused by media with magnetized microstructures, accounting for arbitrary cylinder orientations and validated through simulations.

Contribution

It introduces an analytical expression for Larmor frequency shifts in media with arbitrarily oriented magnetized cylinders, linking microstructure to measurable MRI signals.

Findings

Analytical formula for Larmor frequency shift in media with oriented cylinders

Validation of the model through simulations considering shape and size effects

Framework enables inference of fiber orientation distribution from MRI data

Abstract

We present a theoretical framework for the NMR and MRI measured Larmor frequency in media with magnetized microstructure using the mesoscopic Lorentz sphere and the principle of coarse graining. We obtain an analytical expression for infinite cylinders with arbitrary orientation dispersion and show how it depends on the fiber orientation distribution, measurable using diffusion MRI. Through simulations, we scrutinize the framework including the effect of the shape and size of the Lorentz cavity and validate our result for cylinders.