Wireless Endocavitary Magnetic Resonance Radio Frequency Coil Based on a Near-Field Coupling Array
Mo Zhiguang1,2, Wu Bing3, Zhang Xiaoliang4, Li Ye1,2
1. Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences Shenzhen 518000 China; 2. University of Chinese Academy of Sciences Beijing 101408 China; 3. Shanghai United Imaging Healthcare Co. Ltd Shanghai 200235 China; 4. State University of New York at Buffalo New York 14260 USA
Abstract：Purpose: In magnetic resonance imaging (MRI), conventional sur face radio frequency (RF) coils often exhibit insufficient signal-to-noise ratio (SNR) when imaging deep-seated organs. The study aims to enhance the imaging sensitivity of deep tissues by proposing a coil architecture that integrates a wireless endocavitary RF coil with an external multi-channel surface array, while avoiding significant increases in medical cost or system complexity. Methods: Based on near-field coupling theory, a dual-channel wireless endocavitary coil was designed and implemented, operating inductively with a 24-channel flexible surface array for signal reception. Adjacent wireless elements were decoupled through geometric overlapping, enabling each unit to resonate independently during the signal reception phase. Each element was integrated with a passive detuning circuit, consisting of lumped capacitors, inductors, and bidirectional diodes. During the RF transmission phase, the diodes became forward-biased, forming a parallel resonant circuit with the lumped components. This configuration effectively opened the coil loop, thereby preventing interference with the transmit magnetic field and reducing the risk of specific absorption rate (SAR) increase. An equivalent physical model was established, and an analytical relationship between SNR and coil loading was derived. Theoretical analysis indicated that, while maintaining a large mutual inductance between the wireless and surface coils, minimizing the loading effect of the wireless coil is critical for maximizing SNR. Guided by this principle, the coil was optimized by encapsulating it in three layers of heat-shrink tubing to reduce loading while preserving efficient electromagnetic coupling. Subsequently, B1-field and SAR simulations were conducted to assess field distribution and safety. Imaging experiments were performed on a 5 T whole-body MRI system using recently euthanized adult beagle dogs, to evaluate the proposed design under realistic anatomical conditions. Two configurations were compared under identical geometric positioning and imaging parameters: (1) the dual-channel wireless endocavitary coil combined with the 24-channel surface array, and (2) the surface array alone. Quantitative SNR analysis was performed within regions of interest (ROIs) encompassing the prostate and surrounding tissues. Results: Simulation results demonstrated that the introduction of the wireless coil substantially enhanced the B1- field intensity in the prostate region. SAR simulations confirmed that, owing to its approximately -40 dB detuning performance, the wireless coil did not produce any significant local SAR elevation during transmission, ensuring operational safety. Experimental results further validated the performance of the proposed system: compared with the surface array alone, the inclusion of the wireless endocavitary coil yielded an average SNR improvement of approximately 97% within the prostate ROI, confirming its efficacy in enhancing deep-tissue signal reception. Conclusion: The proposed hybrid design combining a wireless endocavitary coil with a multi-channel surface array provides a feasible and efficient solution for improving MRI sensitivity in deep anatomical regions. The system achieves high SNR without increasing SAR risk, while maintaining a simple structure and low manufacturing cost—making it suitable for disposable clinical use to alleviate hygiene concerns and enhance patient acceptance. Beyond prostate MRI, the proposed approach shows potential for extension to other deep-organ imaging applications, offering a promising direction for next-generation wireless RF coil systems that balance practicality, economy, and image quality.
莫智广, 吴冰, 张笑良, 李烨. 基于近场耦合阵列的腔内磁共振无线射频线圈[J]. 电工技术学报, 2026, 41(17): 5768-5778.
Mo Zhiguang, Wu Bing, Zhang Xiaoliang, Li Ye. Wireless Endocavitary Magnetic Resonance Radio Frequency Coil Based on a Near-Field Coupling Array. Transactions of China Electrotechnical Society, 2026, 41(17): 5768-5778.
[1] Hu Yang, Huang Yiman, Qu Shuxian, et al.Deep-learning-based dual denoising algorithm for shielding-free magnetic resonance imaging[J]. IEEE Transactions on Artificial Intelligence, 2025, 6(10): 2766-2776. [2] Wang Jianbao, Liu Yipeng, Ma Yuhan, et al. In vivo 7 Tesla MRI of non-human primate intracortical microvascular architecture[J]. Neuron, 2025, 113(16): 2621-2635.e5. [3] Yang Xing, Du Feng, Ding Zekang, et al.A quadruple-tuned RF coil system for 1H/19F/23Na/31P synchronous MR imaging and spectroscopy at 3 T[J]. IEEE Transactions on Instrumentation and Measurement, 2025, 74: 4504212. [4] Yang Xing, Gao Shang, Wang Jiasheng, et al.A 2-kW high-efficiency and broadband GaN linear RF power amplifier for multinuclear magnetic resonance imaging[J]. IEEE Transactions on Microwave Theory and Techniques, 2025, 73(9): 6695-6706. [5] Wang Hanlei, Lou Feiyang, Huang Yiman, et al.Extending the MaRCoS: a 4-RX open-source MRI console for low-, mid-, and high-field systems[J]. IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology, 2025, 9(3): 351-359. [6] Chen Qiaoyan, Xie Guoxi, Luo Chao, et al.A dedicated 36-channel receive array for fetal MRI at 3T[J]. IEEE Transactions on Medical Imaging, 2018, 37(10): 2290-2297. [7] Li Ye, Lee J, Long Xiaojing, et al.A magnetic resonance-guided focused ultrasound neuromodulation system with a whole brain coil array for nonhuman Primates at 3 T[J]. IEEE Transactions on Medical Imaging, 2020, 39(12): 4401-4412. [8] Wei Zidong, Zhang Zhilin, Chen Qiaoyan, et al.Open-transmit and flexible receiver array for high resolution ultrahigh-field fMRI of the human sensorimotor cortex[J]. Communications Biology, 2025, 8: 482. [9] Lu Rongsheng, Jiang Xiaowen, Zhang Jinxiang, et al.A novel portable unilateral magnetic resonance magnet for noninvasive quantification of human liver fat[J]. IEEE Transactions on Instrumentation and Measurement, 2023, 72: 4004808. [10] Kong Xiaohan, Shen Sheng, Xu Xianneng, et al.Topology optimization and experimental validation of a magnet structure for portable ultralow-field MRI devices[J]. IEEE Transactions on Instrumentation and Measurement, 2025, 74: 4015610. [11] Yang Lei, He Wei, Shen Sheng, et al.An exploration of parallel imaging system for very-low-field (50 MT) MRI scanner[J]. IEEE Transactions on Instrumentation and Measurement, 2025, 74: 4003713. [12] Zhang Yuxiang, Kong Xiaohan, He Wei, et al.Eddy current characterization using efficient finite element analysis for Z-gradient coils in a low-field MRI scanner[J]. IEEE Transactions on Instrumentation and Measurement, 2025, 74: 4003909. [13] Lu Rongsheng, Liu Siyu, Cai Qingsong, et al.A low-cost low-field nuclear magnetic resonance cryoporometry system for nanopore size measurement[J]. IEEE Transactions on Instrumentation and Measurement, 2022, 71: 6003206. [14] 万裁, 何为, 沈晟, 等. 超低场磁共振膝关节正交接收线圈设计[J]. 电工技术学报, 2024, 39(7): 1923-1931. Wan Cai, He Wei, Shen Sheng, et al.Design of a quadrature receive coil for ultra-low-field knee magnetic resonance imaging[J]. Transactions of China Electrotechnical Society, 2024, 39(7): 1923-1931. [15] Chen Wanqing, Zheng Rongshou, Zhang Siwei, et al.Cancer incidence and mortality in China, 2013[J]. Cancer Letters, 2017, 401: 63-71. [16] 杨庆新, 陈海燕, 徐桂芝, 等. 无接触电能传输技术的研究进展[J]. 电工技术学报, 2010, 25(7): 6-13. Yang Qingxin, Chen Haiyan, Xu Guizhi, et al.Research progress in contactless power transmission technology[J]. Transactions of China Electrotechnical Society, 2010, 25(7): 6-13. [17] 陆晴云, 李德骏, 李泽松, 等. 海洋环境下非接触式电能传输系统的优化设计[J]. 传感器与微系统, 2011, 30(12): 112-115, 118. Lu Qingyun, Li Dejun, Li Zesong, et al.Optimization design of a contactless power transmission system for ocean application[J]. Transducer and Microsystem Technologies, 2011, 30(12): 112-115, 118. [18] 谭林林, 黄学良, 黄辉, 等. 基于频率控制的磁耦合共振式无线电力传输系统传输效率优化控制[J]. 中国科学: 技术科学, 2011, 41(7): 913-919. Tan Linlin, Huang Xueliang, Huang Hui, et al.Optimal control of transmission efficiency of magnetically coupled resonant wireless power transmission system based on frequency control[J]. Scientia Sinica (Technologica), 2011, 41(7): 913-919. [19] 赵争鸣, 张艺明, 陈凯楠. 磁耦合谐振式无线电能传输技术新进展[J]. 中国电机工程学报, 2013, 33(3): 1-13. Zhao Zhengming, Zhang Yiming, Chen Kainan.New progress of magnetically-coupled resonant wireless power transfer technology[J]. Proceedings of the CSEE, 2013, 33(3): 1-13. [20] 程志远, 宋晓逸, 吴晓婷, 等. 无线充电系统旋转式电磁耦合器损耗计算及热点温度研究[J]. 电工技术学报, 2024, 39(7): 1932-1942, 1956. Cheng Zhiyuan, Song Xiaoyi, Wu Xiaoting, et al.Loss calculation and hot spot temperature research of rotary electromagnetic coupler in wireless charging system[J]. Transactions of China Electrotechnical Society, 2024, 39(7): 1932-1942, 1956. [21] 李中启, 张晨曦, 王建斌, 等. 基于变频重构S/SP拓扑的无线电能传输系统恒流恒压研究[J]. 电工技术学报, 2024, 39(15): 4718-4732. Li Zhongqi, Zhang Chenxi, Wang Jianbin, et al.Research on constant current and constant voltage of WPT system based on variable frequency reconfiguration S/SP topology[J]. Transactions of China Electro-technical Society, 2024, 39(15): 4718-4732. [22] 徐先峰, 吴慧玲, 杨雄政, 等. 空间约束下电动汽车无线充电系统磁耦合结构优化[J]. 电工技术学报, 2024, 39(12): 3581-3588. Xu Xianfeng, Wu Huiling, Yang Xiongzheng, et al.Optimization of magnetically coupled structure of wireless charging system for electric vehicles under space constraint[J]. Transactions of China Electro-technical Society, 2024, 39(12): 3581-3588. [23] 宋凯, 朱春波, 李阳, 等. 用于电动汽车动态供电的多初级绕组并联无线电能传输技术[J]. 中国电机工程学报, 2015, 35(17): 4445-4453. Song Kai, Zhu Chunbo, Li Yang, et al.Wireless power transfer technology for electric vehicle dynamic charging using multi-parallel primary coils[J]. Proceedings of the CSEE, 2015, 35(17): 4445-4453. [24] 麦瑞坤, 陈阳, 刘野然. 基于变补偿参数的IPT恒流恒压电池充电研究[J]. 中国电机工程学报, 2016, 36(21): 5816-5821, 6024. Mai Ruikun, Chen Yang, Liu Yeran.Compensation capacitor alteration based IPT battery charging application with constant current and constant voltage control[J]. Proceedings of the CSEE, 2016, 36(21): 5816-5821, 6024. [25] Shchelokova A, Ivanov V, Mikhailovskaya A, et al.Ceramic resonators for targeted clinical magnetic resonance imaging of the breast[J]. Nature Com-munications, 2020, 11: 3840. [26] Chi Zhonghai, Yi Yi, Wang Yakui, et al.Adaptive cylindrical wireless metasurfaces in clinical magnetic resonance imaging[J]. Advanced Materials, 2021, 33(40): 2102469. [27] Li Bingbai, Xie Rongbo, Sun Zhenci, et al.Nonlinear metamaterials enhanced surface coil array for parallel magnetic resonance imaging[J]. Nature Communications, 2024, 15: 7949. [28] Wu Ke, Zhu Xia, Anderson S W, et al. Wireless, customizable coaxially shielded coils for magnetic resonance imaging[J]. Science Advances, 2024, 10(24): eadn5195. [29] Zhu Xia, Wu Ke, Anderson S W, et al.Wearable coaxially-shielded metamaterial for magnetic resonance imaging[J]. Advanced Materials, 2024, 36(31): 2313692. [30] Jia Yuqi, Pang Yanwei, Jin Ruiqi, et al.A unified circular-polarization metamaterial-inspired resonator for increasing SNR in breast MRI[J]. Magnetic Resonance Imaging, 2025, 121: 110403. [31] Lu Ming, Wang Ruilin, Chen Yuanyuan, et al.Detunable wireless ladder resonator inserts for enhanced SNR of local array coil at 1.5T MRI[J]. Medical Physics, 2025, 52(6): 3649-3657. [32] Mo Zhiguang, Che Shao, Du Feng, et al.A near-field coupling array enables parallel imaging and SNR gain in MRI[J]. Advanced Science, 2025, 12(37): e03481. [33] Mo Zhiguang, Xiao Enhua, Hayat S, et al.A wireless endorectal coil based on a near-field coupling array system for prostate MRI[C]//2025 ISMRM & ISMRT Annual Meeting, 2025: 4407. [34] Roemer P B, Edelstein W A, Hayes C E, et al.The NMR phased array[J]. Magnetic Resonance in Medicine, 1990, 16(2): 192-225. [35] Edelstein W A, Glover G H, Hardy C J, et al.The intrinsic signal-to-noise ratio in NMR imaging[J]. Magnetic Resonance in Medicine, 1986, 3(4): 604-618. [36] Schnall M D, Lenkinski R E, Pollack H M, et al.Prostate: MR imaging with an endorectal surface coil[J]. Radiology, 1989, 172(2): 570-574. [37] Ertürk M A, Tian Jinfeng, Van de Moortele P F, et al. Development and evaluation of a multichannel endorectal RF coil for prostate MRI at 7 T in combination with an external surface array[J]. Journal of Magnetic Resonance Imaging, 2016, 43(6): 1279-1287. [38] Arteaga de Castro C S, van den Bergen B, Luijten P R, et al. Improving SNR and B1 transmit field for an endorectal coil in 7 T MRI and MRS of prostate cancer[J]. Magnetic Resonance in Medicine, 2012, 68(1): 311-318. [39] Mo Zhiguang, Zhang Xiaoping, Liang Huageng, et al.A novel three-channel endorectal coil for prostate magnetic resonance imaging at 3T[J]. IEEE Transactions on Biomedical Engineering, 2023, 70(12): 3381-3388.
2026, Vol. 41 
