Magnetic shielding for MRI superconducting magnets

An optical design is presented of a highly homogeneous superconducting coil system with magnetic shielding for magnetic resonance imaging (MRI). The optimal design method is a combination of the hybrid finite-element and boundary-element method for analysis of an axially symmetric nonlinear open-boundary magnetic field problem and a mathematical programming method for solving the corresponding optimization problem. The multiobjective goal programming method and the nonlinear least-squares method are adopted. The optimal design results of 1.5- and 4.7-T-magnet systems with different types of magnetic shielding for whole-body imaging are compared, and the advantages of a combination of active and yoke shields are shown.