开放式低场永磁MRI磁体的匀场方法研究

在开放式低场永磁MRI(magnetic resonance imaging,磁共振成像)生产中,磁体匀场是提高质量和效率的关键技术之一.为解决国内匀场方法缺乏完整理论指导的问题,本文使用磁场球谐函数展开式分析主磁场情况并制定匀场方案.对展开式的低阶项,主动匀场方法十分适用,而对无法使用线圈的特殊情况或消除高阶项时需进行被动匀场.实验中有一组匀场线圈需要较大电流,此时采用永磁材料代替线圈可以达到很好的补偿效果.

Shimming method for permanent magnet of open-type low-field MRI

In the process efficiency and quality. At of producing a permanent magnet, shimming present, for the domestic manufacturers, the one of the key techniques for improving the shimming lack the support of an integral theory. For this reason, the spherical harmonic magnetic field and establishing the project both for active and passive shimming methods of the open type low-field MRI function is introduced in analyzing the . The low-order terms of the spherical harmonic expansion can be easily shimmed by using the shim coil system. However, when the requirements exceed the capabilities of the corresponding active shim device, and when the high-order distortions require to be cancelled, passive shimming is applicable. In the experiment, the shim coils for the A3^0 term that require heavy current can not be realized. Therefore, this paper adopts permanent magnetic material instead of shim coils, achieving good compensation for the magnetic field.