Abstract: 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.

Key words: magnetic resonance imaging, unilateral magnets, slice imaging region, saddle point