An Experimental Study on the Passive Shimming in the 0.5 T Superconducting MRI Magnet

For the superconducting magnetic resonance imaging (MRI) magnet, passive shimming technique in low field is more complicated than that in high field, due to the unsaturated magnetization of the used shim pieces and other issues, such as the oversized minimum shim piece and insufficient accuracy. For common problems of the MRI magnets and the special problems caused by low field, an experimental study was carried out on the 0.5 T superconducting magnets by adopting some improved strategies for passive shimming of low field in this article. Three magnets of the same type were used as experimental objects, and the proven measures were proposed to improve the problems of the unsaturated magnetization, shim piece specification, and position difference. The experimental results showed that the passive shimming reliably enables the static magnetic field of the 0.5 T MRI magnet to achieve the required homogeneity, which have practicality and reference value for the fabrication and shimming of the low-field MRI magnet.