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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 imaging diagnostic equipment, which based on the principles of nuclear magnetic resonance imaging of human organs in the static magnetic field, with high definition and any level of imaging advantages, in medical examination and diagnosis Compared with the low-field MRI, the high-field MRI system can improve the magnetic susceptibility of the proton, increase the signal-to-noise ratio of the image and shorten the MRI signal acquisition time, so that the signal changes of the brain imaging become more obvious. However, High background magnetic field will interfere with the surrounding medical electronic devices, so it is of great significance for the magnetic flux leakage shielding of high-field superconducting magnets.At present, there are two kinds of shielding methods for the escaping magnetic field: active shielding and passive shielding. The former mainly uses reverse Superconducting coils are shielded and the latter are shielded with iron screens.Compared with active screens, ferromagnetic screens do not require additional superconducting coils and can increase the strength of the main magnetic field to some extent, saving more than 30% of superconductivity This paper describes some physical factors to be considered in the design of high-field superconducting magnets, and at the same time optimizes the geometry of the iron screen of the 9.4TMRI system, gives two kinds of optimization With the design model, and optimize the results are analyzed and compared.