Optimized configurations for passively shielded magnetic resonance imaging magnets

A design approach is presented for the development of passive shields for coil configurations, with particular emphasis on those used for magnetic resonance imaging (MRI). The approach is based on minimizing the weight of the shield by ensuring that the shield material is everywhere near saturation. A mathematical model is developed to describe the shielding efficiency of a cylindrical shield as a function of shield geometry and type of shield material. The model is used to develop a possible multiple-shield configuration for a 1.5-T MRI magnet.>