Prediction of motion induced magnetic fields for human brain MRI at 3T

TL;DR

This study develops a simulation-based method to predict head movement-induced magnetic field inhomogeneities in brain MRI at 3T, outperforming traditional transformation approaches and enabling better image quality optimization.

Contribution

The paper introduces a novel simulation approach incorporating local susceptibility and sequence errors to accurately predict B0 field changes due to head movement in MRI.

Findings

Simulation predicts B0 inhomogeneities more accurately than transformation methods.

Using simulated B0 maps improved shim optimization by up to 22.2%.

The method is effective for all head positions, including large movements.

Abstract

Objective Maps of B0 field inhomogeneities are often used to improve MRI image quality, even in a retrospective fashion. These field inhomogeneities depend on the exact head position within the static field but acquiring field maps (FM) at every position is time consuming. Here we explore different ways to obtain B0 predictions at different head positions. Methods FM were predicted from iterative simulations with four field factors: 1) sample induced B0 field, 2) system's spherical harmonic shim field, 3) perturbing field originating outside the field of view, 4) sequence phase errors. The simulation was improved by including local susceptibility sources estimated from UTE scans and position-specific masks. The estimation performance of the simulated FMs and a transformed FM, obtained from the measured reference FM, were compared with the actual FM at different head positions. Results The transformed FM provided inconsistent results for large head movements (>5 degree rotation), while the simulation strategy had a superior prediction accuracy for all positions. The simulated FM was used to optimize B0 shims with up to 22.2% improvement with respect to the transformed FM approach. Conclusion The proposed simulation strategy is able to predict movement induced B0 field inhomogeneities yielding more precise estimates of the ground truth field homogeneity than the transformed FM.