基于人工电磁媒质的新型高场磁共振射频线圈的关键问题研究

Performance of radio-frequency (RF) coils is one of the key bottlenecks of image quality and safety in magnetic resonance imaging (MRI). The main method to improve the performance of RF coils is to optimize the distributions of RF electromagnetic (EM) field in human body. The metamaterials can achieve unique and programmable EM properties beyond those of natural materials. Therefore the metamaterials can be utilized to manipulate the EM field distributions, which provides novel theoretical foundation and technical feasibility to break through this bottleneck. In this project, we focus on the design of advanced RF coils for MR imaging based on the metamaterials. Our preliminary studies demonstrate that EM field distribution with high homogeneity and high magnetic-field-to-electric-field ratio which is difficult to achieve by traditional methods can be obtained by utilizing the programmalbe effective properties of the metamaterials. Combined with RF coil design, the use of metamaterials can improve the homogeneity of transmit field and signal-to-noise ratio (SNR) while reduce the specific absorption rate (SAR). In this project, we propose to explore the mechanism of manipulating EM field distributions by using metamaterials, to demonstrate an integrated design method of metamaterials and RF coil, and to develop fast and in-vivo imaging methods for EM field mapping to validate the theoretic analysis and design results. The success of this proposed project will improve the performance of RF coils, consequenctly enhance the image quality, imaging speed and safety, and therefore provide theoretical and technical foundation for the development of high field MRI technologies.

射频线圈的性能是制约高场磁共振系统图象质量和成像速度的关键瓶颈之一。提高射频线圈性能的主要手段是优化其在人体内的电磁场分布。人工电磁媒质具有自然材料不具备的可人工设计的等效电磁参数，对电磁场有特殊的可控调制，为突破这一瓶颈提供了崭新的理论支持和技术可能。本课题针对基于人工电磁媒质的新型高场磁共振射频线圈，在前期研究基础上，利用人工电磁媒质可设计等效电磁参数的特性，结合射频线圈结构设计，实现传统技术难以产生的均匀的高磁场/电场比的电磁场分布，提高射频发射场均匀度，降低比吸收率，提高图像信噪比。拟探索人工电磁媒质调制射频线圈电磁场分布的机制，阐明人工电磁媒质与射频线圈的一体化设计方法，提出基于磁共振成像技术的快速在体无损射频电磁场测量方法，验证理论分析与设计的结果。本项目的成功实施，有望提高射频线圈的性能，从而提高图像质量、成像速度和安全性，为促进高场磁共振技术的发展提供理论依据与技术基础。

项目按计划执行，完成了相关的研究目标和预期成果。本项目以利用人工电磁媒质提高高场MRI 系统射频线圈的性能为目标，研究其中的关键科学问题和核心技术。从人工电磁媒质对射频电磁场的调制等理论问题出发，开发了人工电磁媒质与射频线圈一体化优化设计的电磁仿真设计方法，优化了微结构形状参数，制备了人工电磁媒质样品，进行了实验测量，分析对比优化，形成一个完整的研发流程。开发的高场MRI系统多通道射频接收线圈性能满足临床的需求。.项目预期在国内外核心学术杂志上发表论文8-10 篇，其中SCI 收录论文5-7 篇。申请中国发明专利3-5 项，授权2 项。参加IEEE、ISMRM 等国际学术会议3-5 人次，发表会议论文3-5 篇。邀请国际著名学者来华交流2 次，培养研究生2-3 名。通过本项目的顺利实施，各项指标均达到或超过预期目标，其中在国内外学术期刊和国际会议上发表论文13篇，被SCI收录11篇、EI收录4篇，项目执行期内授权国家发明专利9项，申请中的国家发明专利6项。组织国际学术会议并邀请国际著名学者来华交流2次。结合本项目的研究，培养硕士研究生4名。