Synergistic Active & Passive Shimming to Optimize B0 Field Homogeneity in Micro MR Imaging

Rahul Dewal¹, Zhipeng Cao², Christopher Sica³, Christopher Collins³, Qing Yang^1,3

Passive shimming can be used to correct for the static B₀ field inhomogeneities caused by air-tissue boundaries in the sinus cavities and ear canals. By placing pieces of shim material with high susceptibility values into the magnet at precise locations, the magnetic field can be perturbed such that higher-order inhomogeneities are corrected. This method uses a numerical optimization algorithm in conjunction with a Fourier transform-based fast magnetic field calculation method to determine the optimal configuration of shim materials for an agar gel phantom. Optimized active shims are calculated alongside passive shim optimization to form a synergistic shimming approach.