基于硅钢片均一化的超低场磁共振抗涡流<em>Z</em>梯度线圈设计方法

doi:10.19595/j.cnki.1000-6753.tces.240166

Abstract
Figure/Table
References
Related Citation (10)

Download: PDF (7058 KB) HTML (1 KB)
Export: BibTeX | EndNote (RIS)

Abstract In ultra-low field magnet magnetic resonance imaging (MRI) devices, ferromagnetic materials such as anti-eddy current plates and yokes can affect the gradient magnetic field in the imaging target area. Meanwhile, during the operation of gradient coils, especially the Z-direction gradient coil, induced eddy currents can lead to imaging artifacts. This paper proposes a design method for a planar eddy current-resistant Z-gradient coil for permanent magnet ultra-low field MRI devices.
Firstly, the ferromagnetic materials on the outer side of the coil are equivalently simplified. The complex eddy current shield structure (formed by stacking silicon steel sheets) with high magnetic permeability is simplified into a homogeneous magnetic plate structure. In general, conducting structures with high permeability closed to gradient coils can affect the magnetic field, and laminated structures can cause large computations. An analytical solution for the effective permeability of an anti-eddy current plate is introduced, and the laminated structure is reduced to the homogeneous magnetic plate. Thus, the simplified structure combined with the mirror current method introduces the influence of ferromagnetic materials on the gradient coil design process. Subsequently, a parameterized design method for a planar eddy current-resistant Z gradient coil is proposed. By parameterizing the coil structure, direct multi-objective rapid optimization of the final winding structure of the Z-direction gradient coil is achieved. At the same time, additional reverse current windings are implemented on the outer side of the coil to mitigate the eddy current effects. In detail, the structure of the proposed planar Z gradient coils is pre-defined as two groups of clockwise and anticlockwise spiral lines, which are parameterized to a set of points in the x-axis. Then, a multi-objective optimization is performed to obtain the point’s position considering the gradient coil’s maximum nonlinearity, efficiency, and stray magnetic field.
While ensuring coil efficiency (200 μT/(m·A)) and maximum nonlinearity (less than 5%), the maximum stray magnetic field on the outer side of the coil target plane is reduced by 52%. Finite element simulations and gradient field measurements are performed. By simulations, the errors between complete and simplified system models in coil efficiency and maximum nonlinearity are less than 4% and 0.1%, respectively. Also, the differences between simulation and measurement results for the complete model are less than 3% for efficiency and 1% for nonlinearity. Finally, the eddy current-resistant performance of the designed Z-gradient coil is verified through finite element simulations. Moreover, imaging experiments are implemented, and fewer image artifacts can be found.
Compared to conventional design methods, the proposed one considers the influence of high-permeability materials and eddy-current effects. The model simplification is also suitable for gradient coil design for other directions, which can be utilized for system eddy current characterizations. Future works may focus on quantitively evaluating the coils’ anti-eddy current effects and the impact of reverse current on coil efficiency in the design process.

Key words： Magnetic resonance imaging active shielded gradient coil electromagnetic field inverse problem ferromagnetic structure simplification

Received: 24 January 2024

PACS:

TM12

	Service

	E-mail this article
	Add to my bookshelf
	Add to citation manager
	E-mail Alert
	RSS
	Articles by authors
	Zhang Yuxiang
	He Wei
	Kong Xiaohan
	Xuan Liang
	Xu Zheng

Cite this article:

Zhang Yuxiang,He Wei,Kong Xiaohan等. A Design Method for Eddy Current-Resistant Z-Gradient Coil in Ultra-Low Field Magnetic Resonance Imaging Systems Based on Homogeneous of Silicon Steel Sheets[J]. Transactions of China Electrotechnical Society, 2025, 40(4): 987-996.

URL:

https://dgjsxb.ces-transaction.com/EN/10.19595/j.cnki.1000-6753.tces.240166 OR https://dgjsxb.ces-transaction.com/EN/Y2025/V40/I4/987

[1] 陈顺中, 王秋良, 孙万硕, 等. 3 T动物磁共振成像传导冷却超导磁体研究[J]. 电工技术学报, 2023, 38(4): 879-888.
Chen Shunzhong, Wang Qiuliang, Sun Wanshuo, et al.The study of a 3 T conduction-cooled superconducting magnet for animal magnetic resonance imaging[J]. Transactions of China Electrotechnical Society, 2023, 38(4): 879-888.
[2] 曲洪一, 刘鑫, 王晖, 等. 磁共振成像磁体无源匀场改进策略及实验研究[J]. 电工技术学报, 2022, 37(24): 6284-6293.
Qu Hongyi, Liu Xin, Wang Hui, et al.Improved strategy and experimental research on passive shimming in magnetic resonance imaging magnet[J]. Transactions of China Electrotechnical Society, 2022, 37(24): 6284-6293.
[3] 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 orthogonal receiving coil for ultra-low field magnetic resonance knee joint[J]. Transactions of China Electrotechnical Society, 2024, 39(7): 1923-1931.
[4] Yang Lei, He Wei, He Yucheng, et al.Active EMI suppression system for a 50 mT unshielded portable MRI scanner[J]. IEEE Transactions on Bio-Medical Engineering, 2022, 69(11): 3415-3426.
[5] Liu Yilong, Leong A T L, Zhao Yujiao, et al. A low-cost and shielding-free ultra-low-field brain MRI scanner[J]. Nature Communications, 2021, 12: 7238.
[6] He Yucheng, He Wei, Tan Liang, et al.Use of 2.1 MHz MRI scanner for brain imaging and its preliminary results in stroke[J]. Journal of Magnetic Resonance, 2020, 319: 106829.
[7] 孔晓涵, 张雅娜, 吴嘉敏, 等. 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[J]. 电工技术学报, 2024, 39(13): 3917-3927.
Kong Xiaohan, Zhang Yana, Wu Jiamin, et al.Signalto-noise ratio enhancement method for ultra-low field magnetic resonance imaging based on low-frequency surface metamaterials[J]. Transactions of China Electrotechnical Society, 2024, 39(13): 3917-3927.
[8] 闫孝姮, 淡新贤, 陈伟华, 等. 基于改进目标场法梯度线圈的感应式磁声磁粒子浓度成像研究[J]. 电工技术学报, 2024, 39(14): 4305-4316.
Yan Xiaoheng, Dan Xinxian, Chen Weihua, et al.Study on inductive magneto-acoustic magnetic particle concentration imaging based on improved target field gradient coil[J]. Transactions of China Electrotechnical Society, 2024, 39(14): 4305-4316.
[9] 贺中华, 何为, 贺玉成, 等. 皮肤烧伤深度检测的单边核磁共振浅层成像磁体系统[J]. 电工技术学报, 2019, 34(3): 449-458.
He Zhonghua, He Wei, He Yucheng, et al.Unilateral nuclear magnetic resonance superficial imaging magnet system for skin burn depth assessment[J]. Transactions of China Electrotechnical Society, 2019, 34(3): 449-458.
[10] Poole M, Bowtell R.Novel gradient coils designed using a boundary element method[J]. Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering, 2007, 31B(3): 162-175.
[11] Crozier S, Forbes L K, Doddrell D M.The design of transverse gradient coils of restricted length by simulated annealing[J]. Journal of Magnetic Resonance, Series A, 1994, 107(1): 126-128.
[12] Shou Guofa, Xia Ling, Liu Feng, et al.MRI coil design using boundary-element method with regularization technique: a numerical calculation study[J]. IEEE Transactions on Magnetics, 2010, 46(4): 1052-1059.
[13] Wang Yaohui, Liu Feng, Zhou Xiaorong, et al.Design of transverse head gradient coils using a layer-sharing scheme[J]. Journal of Magnetic Resonance, 2017, 278: 88-95.
[14] Wong E C, Jesmanowicz A, Hyde J S.Highresolution, short echo time MR imaging of the fingers and wrist with a local gradient coil[J]. Microbiology Resource Announcements, 1991, 181(2): 393-397.
[15] Ning Feipeng, Wang Meifen, Yang Huan, et al.Physical design of high gradient superconducting magnetic separation magnet for Kaolin[J]. IEEE Transactions on Applied Superconductivity, 2012, 22(3): 3700104.
[16] Zhang Peng, Shi Yikai, Wang Wendong, et al.A spiral, bi-planar gradient coil design for open magnetic resonance imaging[J]. Technology and Health Care, 2018, 26(1): 119-132.
[17] Xuan Liang, Kong Xiaohan, Wu Jiamin, et al.A smoothly-connected crescent transverse gradient coil design for 50 mT MRI system[J]. Applied Magnetic Resonance, 2021, 52(6): 649-660.
[18] Yang Jianzhi, Zhang Xu, Han Bangcheng, et al.Design of biplanar coils for degrading residual field in magnetic shielding room[J]. IEEE Transactions on Instrumentation and Measurement, 2021, 70: 1-10.
[19] Zhao Fengwen, Zhou Xiangyang, Zhou Weiyong, et al.Research on the design of axial uniform coils for residual field compensation in magnetically shielded cylinder[J]. IEEE Transactions on Instrumentation and Measurement, 2022, 71: 4006309.
[20] Roshen W A, Turcotte D E.Planar inductors on magnetic substrates[J]. IEEE Transactions on Magnetics, 1988, 24(6): 3213-3216.
[21] Roshen W A.Effect of finite thickness of magnetic substrate on planar inductors[J]. IEEE Transactions on Magnetics, 1990, 26(1): 270-275.
[22] Kong Xiaohan, Xu Zheng, Shen Sheng, et al.Gradient coil design method specifically for permanentmagnet-type low field portable MRI brain scanner[J]. IEEE Transactions on Instrumentation and Measurement, 2023, 72: 4000512.