Optimal design of MRI magnets with magnetic shielding

A novel optimal design method has been developed for a highly homogeneous superconducting coil system with magnetic shielding for magnetic resonance imaging (MRI). The design method is based on a combination of the hybrid finite-element-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 goal programming and the nonlinear least-squares methods have been adopted. The relative merits of a combination of an active shielding and a room shielding have been investigated. The proposed design method can optimize both an MRI magnet and its magnetic shielding system simultaneously, taking into account the maximum permissible intensity of stray field at a specified distance from the magnet center. Several design procedures and results of a 1-T magnet system are shown.>