反演法在磁共振射频场设计与优化中的应用  

An Inverse Method Used For the Design and Optimization of Radiofrequency Field in MRI

作　　者：曾雁冰[1] 张战胜[2] 辛学刚[2] 

机构地区：[1]广州军区广州总医院附属157医院,广东广州510510 [2]南方医科大学生物医学工程学院,广东广州510515

出　　处：《中国医学物理学杂志》2013年第4期4272-4277,共6页Chinese Journal of Medical Physics

基　　金：国家自然科学基金面上项目(No.61172034)

摘　　要：目的:研究反演法在磁共振射频场设计与优化中的应用,分析比较不同优化函数在射频场设计与优化中的不同作用。方法:根据不同临床诊断或科研需求确定感兴趣区域(Region of Interest,ROI)以及射频场分布,设计目标函数;应用数学中的反演法,根据电流密度和磁场分布之间关系,依据洛伦茨法则(Lorentz Gauge)推导出目标磁场分布与电流密度分布之间的关系表达式,计算射频场的电流密度分布,针对计算过程中出现的积分函数高病态问题,采用不同的优化补偿函数,得到能够产生该射频场的电流密度分布;采用流函数技术将电流密度分布转化为电流分布轮廓,并检验该电流分布轮廓在ROI内的磁场分布是否满足目标磁场的要求,比较不同优化函数的在设计射频场过程中的效果。结果:以反演法为基础优化设计的电流分布轮廓,结构简单、分布平滑便于工程实现,ROI内的射频场分布均匀,磁场强度符合理论设计要求。结论:基于反演法设计的射频场在ROI内的分布符合目标磁场要求,说明我们提出的优化方案在射频场设计与优化中具有优越性,为磁共振射频场的设计提供了一种新的优化方法。Objective： In this paper, an inverse method is presented for the design and optimization of the radiofxequency （RF） field in MRI, Analysis and compare the different role of the different optimization function in the design and optimization ofra- diofrequency fields. Methods： According to the clinical need, the region of interest is set, and a target field function is created based on the inverse technique. According to the relation between current density and magnetic field strength, combined with laws of Lorentz Gauge, The current density of the RF field is calculated accordingly. This is a highly ill-posed problem and a regularization strategy is introduced. After the ill-posed problem is solved, the contour chart of the current density is obtained by using the stream fimction technique. The accuracy of magnetic field within the region of interest induced by the current dis- tribution is verified. Results： Based on the inverse method, much higher homogeneous and better linearity RF field is success- fully obtained within the ROI. The contour chart of the current distribution is available simple structure, smooth distribution that easily engineering implementation. Conclusions： The obtained RF field within the ROI conforms to the requirement of the tar- get magnetic field. The proposed regularization strategy for the design and optimization of the RF field is capable, provides a new method for the MRI RF field designing and optimization.

关 键 词：磁共振成像 射频场 反演法 正则化技术 流函数技术 

分 类 号：O441.4[理学—电磁学]