Hybrid Active and Passive Local Shimming (HAPLS) Targeting Ultra-high-order B0 Spherical Harmonic (SH) Terms in Two-Region MRI

An MRI scanner equipped with global shim systems fails to reach state-of-the-art when shimming two isolated ROIs simultaneously for two reasons: non-optimal spherical harmonic based shimming routine, and significant high-order B0 inhomogeneities, even though the two-area shimming can be essential in scan scenarios, such as bilateral breasts or dyadic brains. To address these challenges, a hybrid active and passive local shimming (HAPLS) technique is proposed to shim two isolated areas in one FOV simultaneously. Both the simulation and experimental results validated that HAPLS can complementarily address the bifocal and high-order inhomogeneities, and locally improve in vivo B0 homogeneity as well.