磁共振成像磁体无源匀场改进策略及实验研究  

Improved Strategy and Experimental Research on Passive Shimming in Magnetic Resonance Imaging Magnet

作　　者：曲洪一 刘鑫[2,3] 王晖 刘建华[1,2] 王秋良[1,2,3] Qu Hongyi;Liu Xin;Wang Hui;Liu Jianhua;Wang Qiuliang(Institute of Electrical Engineering Chinese Academy of Science,Beijing 100190 China;Ganjiang Innovation Academy Chinese Academy of Sciences,Ganzhou 341000 China;College of Rare Earths University of Science and Technology of China,Hefei 230026 China)

机构地区：[1]中国科学院电工研究所,北京100190 [2]中国科学院赣江创新研究院,赣州341000 [3]中国科学技术大学稀土学院,合肥230026

出　　处：《电工技术学报》2022年第24期6284-6293,共10页Transactions of China Electrotechnical Society

基　　金：科技部重点研发计划(2019YFC0117604);江西省自然科学基金(20212BAB214050)资助项目。

摘　　要：无源匀场用于修正磁共振成像磁体不均匀的磁场,是一个非常耗时的过程,包括磁场测绘、优化分析、方案制定、工程实施等步骤。由于存在不可避免的计算误差,无源匀场需要多次重复以上步骤(迭代)才能获得满足要求的高均匀度静磁场,目前相关研究主要集中于优化模型的构造或求解算法的改进,研究手段通常是数值模拟法,忽略了匀场实践中遇到的问题,更没有基于匀场过程工艺的优化。为了提高匀场的性能和效率,该文提出了一些磁共振成像(MRI)磁体无源匀场技术的改进策略:测量多个样片的实际磁场以校正磁化场计算;以目标磁场为变量构建线性优化模型;采用“奇偶”匀场法减少匀场系统的拆装次数。最后,在一台1.5T MRI超导磁体上实施了改进的无源匀场技术验证实验,结果显示,仅通过两次迭代即可获得满足成像要求的磁场均匀度,并且在第三次迭代后达到设计值。与改进前的实验结果相比,新的匀场策略具有显著的成效。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.

关 键 词：磁共振成像磁体 无源匀场 校正模型 “奇偶”匀场法 

分 类 号：TM153[电气工程—电工理论与新技术]