High resolution simulation and measurement demonstrate oscillatory spatiotemporal B₀ fluctuations across the human...

Functional cardiac MRI scans employing balanced steady-state free precession sequences suffer from dark band artifacts in the myocardium due to B₀ inhomogeneity. We recently introduced a novel method for the theoretical derivation of B₀ distributions in the human heart. This study aims to simulate the B₀ distributions in the heart across the cardiac cycle using structural MR images and validate the simulations via in vivo measured cardiac phase-specific B₀ maps on the same subjects at 3T.

Cardiac phase-specific B₀ field maps were acquired from eight healthy subjects at 3T. B₀ conditions were simulated based on tissue masks created from the cardiac-phase specific structural images from the in vivo B₀ map scan and anatomical images from a thoracic MRI scan, adopting our recently published approach. The simulations and in vivo measurements were compared by calculating the spatial correlation of their B₀ distributions and temporal correlation of the derived spherical harmonic coefficients throughout the cardiac cycle.

The spatial comparison of B₀ maps between the simulation and in vivo measurement indicates an overall average correlation coefficient of 0.91 across the cardiac cycle in all subjects. Both groups show consistent high-level B₀ patterns. Temporal variations of B₀ conditions exhibit sinusoidal characteristics and are strongly correlated between simulation and in vivo.

Theoretical simulations employing regional anatomical features were validated by direct in vivo B₀ mapping in the same subjects. The spatial B₀ condition throughout the cardiac cycle exhibits oscillatory characteristics due to structural distortions of cardiac motion.