材料期刊网

磁共振成像（MRI）系统是一种重要的医学影像诊断设备,它根据核磁共振原理对处于静磁场中的人体器官进行成像,具有清晰度高和任意层面成像等优点,在医学检查和诊断方面有着重要的作用,与低场MRI相比,高场MRI系统可提高质子的磁化率,增加图像的信噪比,缩短MRI信号采集时间,从而使脑功能成像的信号变化更为明显;但是较高的背景磁场会对周围医学电子设备的干扰,因此对于高场超导磁体漏磁的屏蔽具有重要意义.目前对逸散磁场的屏蔽方式有主动屏蔽和被动屏蔽两种,前者主要使用反向超导线圈进行屏蔽,后者使用铁屏进行屏蔽.与主动屏蔽相比,铁磁屏蔽无需附加超导线圈,且能在一定程度上增大主磁场的强度,可以节省30%以上的超导线材用量.本文阐述了高场超导磁体设计中要考虑的一些物理因素,同时针对9.4TMRI系统铁屏的几何结构进行优化设计,给出两种不同的设计模型,并对优化结果进行了分析和比较.

Magnetic resonance imaging（MRI） system is an important medical diagnostic equipment.Based on the principle of magnetic resonance in static magnetic field,it offers imaging of human organs at any level with high definition,thus playing an important role in medical examination and diagnosis.Compared with low-field MRI,high field MRI system can improve proton magnetic susceptibility,increase signal-to-noise ratio,reduce the acquisition time,so that the signal changes of brain imaging is more obvious.However,superconducting magnets used in high field MRI systems usually produce high leakage field,which poses great impact on surrounding equipments,so that a practicable and effective shielding method is needed.Due to its low cost and ease to build,iron shielding is universally used,but mainly in low field environment.In the present paper,some physical factors for designing high-field superconducting magnets are firstly discussed,then a method for shape optimization of iron shield for high field magnets is provided.Our procedure is based on a cooperative Integrated Design Optimization Platform（CIDO）,which is suited to analysis of large,complicated nonlinear magnetic problems.At last,the optimal design results of 9.4 Tesla magnet systems with different iron shielding models have been presented.