电工技术学报2025，Vol.40Issue(4)：987-996,10.DOI:10.19595/j.cnki.1000-6753.tces.240166
基于硅钢片均一化的超低场磁共振抗涡流Z梯度线圈设计方法
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
摘要
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.关键词
磁共振成像/梯度线圈/电磁场逆问题/铁磁结构简化Key words
Magnetic resonance imaging/active shielded gradient coil/electromagnetic field inverse problem/ferromagnetic structure simplification分类
信息技术与安全科学引用本文复制引用
张宇翔,何为,孔晓涵,宣亮,徐征..基于硅钢片均一化的超低场磁共振抗涡流Z梯度线圈设计方法[J].电工技术学报,2025,40(4):987-996,10.基金项目
国家自然科学基金(52077023)和重庆科卫联合基金(2023MSXM016)资助项目. （52077023）
