Passive shimming of a superconducting magnet using the L1-norm regularized least square algorithm

Journal of Magnetic Resonance
Xia KongS Crozier

Abstract

The uniformity of the static magnetic field B0 is of prime importance for an MRI system. The passive shimming technique is usually applied to improve the uniformity of the static field by optimizing the layout of a series of steel shims. The steel pieces are fixed in the drawers in the inner bore of the superconducting magnet, and produce a magnetizing field in the imaging region to compensate for the inhomogeneity of the B0 field. In practice, the total mass of steel used for shimming should be minimized, in addition to the field uniformity requirement. This is because the presence of steel shims may introduce a thermal stability problem. The passive shimming procedure is typically realized using the linear programming (LP) method. The LP approach however, is generally slow and also has difficulty balancing the field quality and the total amount of steel for shimming. In this paper, we have developed a new algorithm that is better able to balance the dual constraints of field uniformity and the total mass of the shims. The least square method is used to minimize the magnetic field inhomogeneity over the imaging surface with the total mass of steel being controlled by an L1-norm based constraint. The proposed algorithm has been...Continue Reading

References

Mar 1, 1984·Magnetic Resonance in Medicine : Official Journal of the Society of Magnetic Resonance in Medicine·F Roméo, D I Hoult

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Citations

Oct 3, 2019·The Review of Scientific Instruments·Yaohui WangFeng Liu

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