磁共振成像磁体无源匀场改进策略及实验研究

Passive shimming is used to correct the inhomogeneous magnetic field of the MRI magnets. Due to the inevitable calculation errors, passive shimming must be repeated many times (iteration) to obtain a required high homogeneous static magnetic field. At present, the relevant research mainly focuses on constructing the optimization model or improving the solution algorithm. The research method is usually the numerical simulation method, ignoring the problems encountered in the shimming practice, and there is no optimization based on the shimming process. To improve the performance and efficiency of shimming, this paper presented an improved strategy for the passive shimming technology in MRI magnets: measuring the actual magnetic field of multiple representative pieces to correct the calculation; constructing a linear optimization model with the target magnetic field as a variable; adopting “Odd-Even” approach to simplify the assembly of the shim system. Finally, the experiment for the improved shimming technology was performed on a 1.5T MRI superconducting magnet. The results show that the magnetic field homogeneity that meets the imaging requirements could be obtained only through two iterations, and the design value was reached after the third iteration. Compared with the results of the method before improvement, the new shimming strategy has a significant effect.