基于目标场点法和流函数的磁共振有源匀场线圈设计方法

Method of designing magnetic resonance active shimming coil based on target field point method and flow function

磁场均匀性是磁共振系统的重要参数,提高磁场均匀性有助于磁共振时域信号的检测和磁共振频域信号分辨率的改善.基于有源匀场连续电流密度分布的思想,采用目标场点法和流函数结合的方法设计匀场线圈,即由毕奥-萨伐尔定律确定磁场分布与电流密度的关系,约束线圈半径和设置约束点后,根据目标场分布逆向求解线圈平面的电流密度分布,再用流函数将电流密度分布离散化处理,得到匀场线圈的绕线位置分布.根据电磁仿真计算结果制作包含一阶与二阶匀场线圈应用于磁共振分析仪,实验验证表明该匀场线圈能有效地改善永磁体核磁共振系统磁场的均匀性.

Uniformity of magnetic field is an important parameter of magnetic resonance system.Improving the uniformity of magnetic field is helpful for detecting the magnetic resonance time domain signal and improving the resolution of magnetic resonance frequency domain signal.Based on the idea of continuous current density distribution in an active shimming field,the shimming coil is designed by combining the target field point method with the current function method.That is to say,the relationship between magnetic field distribution and current density is determined by Biot-Savart law.After confining the coil radius and setting the constraint point,the current density distribution on the coil plane is inversely solved according to the target field distribution.Then the current density distribution is discretized by the current function,and the winding position distribution of the uniform field coil is obtained.According to the results of electromagnetic simulation,the first-order and second-order shimming coils are fabricated and applied to the magnetic resonance analyzer.The experimental results show that the shimming coils can effectively improve the magnetic field uniformity of the permanent magnet in nuclear magnetic resonance(NMR) system.