基于低频表面超材料的超低场磁共振成像信噪比增强方法  

Signal-to-Noise Ratio Enhancement Method for Ultra-Low Field Magnetic Resonance Imaging Based on Low-Frequency Surface Metamaterials

作　　者：孔晓涵 张雅娜 吴嘉敏 贺玉成 徐征[1] Kong Xiaohan;Zhang Yana;Wu Jiamin;He Yucheng;Xu Zheng(School of Electrical Engineering Chongqing University,Chongqing 400044,China;Shenzhen Academy of Aerospace Technology,Shenzhen 518057,China;School of Mechatronics Engineering Harbin Institute of Technology,Harbin 150001,China)

机构地区：[1]重庆大学电气工程学院,重庆400044 [2]深圳航天科技创新研究院,深圳518057 [3]哈尔滨工业大学机电工程学院,哈尔滨150001

出　　处：《电工技术学报》2024年第13期3917-3927,共11页Transactions of China Electrotechnical Society

基　　金：国家自然科学基金项目(52077023);深圳科创委承接国家重大科技项目(CJGJZD20200617102402006);深圳市科技重大专项(KJZD20230923114110019)资助。

摘　　要：超低场磁共振成像(ULF-MRI)设备具有成本低、质量轻、体积小等优点,在特殊领域的应用需求越来越大,如移动磁共振成像救护车、床旁监护、偏远地区等。但由于其磁场强度低,导致信噪比也较低,图像分辨率差,因此提升信噪比对促进ULF-MRI技术的发展具有重要意义。该文基于低频表面超材料的特性,提出一种电感-电容谐振阵列,用来提升ULF-MRI的信噪比。首先,建立了等效电路模型来评估磁场增强效果;其次,利用部分元等效电路法计算射频线圈的等效电阻和信噪比,根据成像要求设计优化谐振线圈结构,并提出考虑谐振耦合的匹配方法和线圈阵列的解耦方法。最后,利用自主研发的54.6 mT的ULF-MRI系统(工作频率:2.32 MHz)进行成像实验,图像信噪比得到显著提高。Ultra-low field magnetic resonance imaging(ULF-MRI)offers the benefits of compact size and lightweight.However,the imaging signal-to-noise ratio(SNR)is lower due to limitations in the main magnetic field strength.Thus,a resonant coil array is used for localized signal enhancement in ULF-MRI at 54.6 mT(at a frequency of 2.32 MHz).Given the significant frequency contrast with high-field MRI,the application and design approach for resonant coils in ULF-MRI is presented.The principle is explained using an equivalent circuit.The resonant coil is positioned on the surface of the sample,coaxially aligned with the radio frequency(RF)receiving coil for maximum enhancement.It's tuned to the resonant frequency with an additional capacitor.During RF reception,the coil amplifies the local RF magnetic field,enhancing the received magnetic resonance signals and improving the SNR of the image.A matching method for the receiving coil with the resonance coil is introduced.Due to the strong coupling between the resonant coil and the receiving coil,traditional methods of matching the receiving coil become ineffective.An appropriate deviation of the matching capacitor for the resonant coil is required to maximize the transfer factor from the receiving coil to the preamplifier.The optimization design of the resonant coil is then carried out using a combination of the partial element equivalent circuit(PEEC)method and unitary design.The PEEC method allows rapid calculation of the AC resistance,while the uniform design method facilitates the selection of optimal coil structures under multiple constraints and design objectives.Finally,an overlapped decoupling approach minimizes the coupling between individual coils within the resonant coil array,and the optimum center-to-center distance between the coils is given.For the single resonant coil,simulation and imaging results show that the SNR enhancement decreases with distance.The overall SNR remains higher than in the absence of resonant coils.Clear trends in the imaging results for a 5.5

关 键 词：磁共振成像 射频线圈 低频超材料 信噪比 

分 类 号：TM153[电气工程—电工理论与新技术]