Openness is a desired property for the magnets used in magnetic resonance imaging (MRI). For this reason,the design and making of unilateral magnets,which give a homogenous region,usable for imaging,that is external or "remote" from the magnet,has been attracting more and more attention and research interests. In this paper,the feasibility of designing a unilateral MRI magnet with a slice-shaped imaging region is discussed on the basis of the theory of saddle point. The properties of magnetic fields generated by different types of unilateral magnets were derived by simulation,and the results showed that it is possible to have a unilateral magnet that can generate remote saddle points in the field profile while having sources on one side. The configuration of a unilateral permanent magnet specially designed for MRI is presented,which can produce a slice-shaped imaging region with high field homogeneity. The results obtained in this study will build a strong basis for future scientific researches on fully opened MRI system with homogeneous magnetic field.%单边磁共振成像(MRI)系统由于其良好的开放性引起了越来越多的关注,这种系统的成像样品区位于磁体外侧,其形状为薄片形,其磁体结构设计是一个全新的问题. 本文基于鞍点理论,探索这种单边磁体在其外侧产生均匀样品区的可行性,通过对几种单边磁体结构磁场特性的研究, 指出适当设计的永磁磁体能够在磁体外侧产生鞍点. 最后给出一种符合成像要求的单边永磁MRI磁体结构. 单边MRI磁体结构的可行性分析及磁体结构的成功设计,为开展完全开放式磁共振成像装置的研究打下了坚实的基础.
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