An Optimized Passive Shimming Method for Bi-planar Permanent MRI Magnets

Abstract

An optimized passive shimming method with iron shims is presented in this paper. First, the influence value of a single iron or magnetized shim is fast calculated and determined by analytic solution with a single practical measurement. Then, the correlation between the influence value and parameters of a single shim is analyzed, and the proper parameters, including the position, polarity, and size (radius and thickness), of the shimming pieces are well selected. Finally, the numbers and locations of the passive shims are optimized by mixed-integer linear programming method based on a modified central magnetic field. The optimized method is applied to a 0.5 T Bi-planar permanent magnet magnetic resonance imaging system, and the presented results prove the efficacy of this optimized passive shimming methodology.