梯度 Z 线圈在永磁 MRI 磁体中感应涡流的有限元分析。

Finite element analysis of gradient z-coil induced eddy currents in a permanent MRI magnet.

机构信息

Department of Biomedical Engineering, Zhejiang University, Hangzhou 310027, China.

出版信息

J Magn Reson. 2011 Jan;208(1):148-55. doi: 10.1016/j.jmr.2010.10.017. Epub 2010 Nov 4.

DOI:10.1016/j.jmr.2010.10.017

Abstract

In permanent magnetic resonance imaging (MRI) systems, pulsed gradient fields induce strong eddy currents in the conducting structures of the magnet body. The gradient field for image encoding is perturbed by these eddy currents leading to MR image distortions. This paper presents a comprehensive finite element (FE) analysis of the eddy current generation in the magnet conductors. In the proposed FE model, the hysteretic characteristics of ferromagnetic materials are considered and a scalar Preisach hysteresis model is employed. The developed FE model was applied to study gradient z-coil induced eddy currents in a 0.5 T permanent MRI device. The simulation results demonstrate that the approach could be effectively used to investigate eddy current problems involving ferromagnetic materials. With the knowledge gained from this eddy current model, our next step is to design a passive magnet structure and active gradient coils to reduce the eddy current effects.

摘要

在永磁磁共振成像（MRI）系统中，脉冲梯度场会在磁体结构的导体中产生强涡流。这些涡流会干扰图像编码的梯度场，导致磁共振图像失真。本文提出了一种全面的有限元（FE）分析方法，用于分析磁体导体中的涡流产生。在所提出的 FE 模型中，考虑了铁磁材料的磁滞特性，并采用了标量 Preisach 磁滞模型。该 FE 模型被应用于研究 0.5T 永磁 MRI 设备中梯度 z 线圈引起的涡流。模拟结果表明，该方法可有效用于研究涉及铁磁材料的涡流问题。通过对这个涡流模型的了解，我们的下一步是设计无源磁体结构和有源梯度线圈来减少涡流的影响。