This article presents a methodology of simulation-based design of magnetic resonance imaging (MRI) magnets, modified with a symmetric ferromagnetic shell. The design methodology employs the gradient-based optimization solver of COMSOL Multiphysics to obtain an optimum geometrical arrangement of symmetrical electromagnets in the MRI system. The aim of this article is to design an MRI magnet system, modified with a ferromagnetic shell, which can operate at minimum possible current, can provide a critical level of field homogeneity within the spherical imaging volume, and has magnetic coils with shorter radii. The optimized design solution provides the dimensions of coil blocks, dimensions of ferromagnetic shell, the total length of conductor in each coil block, positions of the coil blocks, current, and the resultant magnetic field. This article reveals that the modification of an MRI system with a ferromagnetic shell significantly improves the field uniformity within a central spherical zone having a diameter of 40-50 cm and greatly reduces the current requirement. The design methodology adopted in this study can be extended to other kinds of configurations.
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Oraon et al. (2020) studied this question.