  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.
