An optimized design approach for 14 T actively shielded MRI magnets

In this paper, an optimized method to design superconducting magnets for 14T actively shielded MRI is proposed. At first, the feasible current-carrying region assumed as possible coil zone is subdivided into two-dimensional array grids, in which each grid represents one loop of a current-carrying conductor. Then the current distribution is obtained using linear programming by a detailed consideration of the superconductor consumption, central field strength, imaging region homogeneity and stray field leakage range. Afterwards the rectangular section of the magnet is obtained by reshaping the irregular current region and the method of non-linear programming is then adopted to refine each section's position and size to obtain the final magnet configurations. In addition, the spherical harmonics elimination for the central magnetic field is proposed as the optimization strategy used in the non-linear programming method to get the least level of inhomogeneity over the imaging region and all the current centers are chosen based on the locations of actual superconducting wires of each conductor. Finally this combined design method has obtained high field homogeneity in the central zone by four sets of coils with a total length around 3.5 m and inner diameter nearly 1 m. The detailed analysis and optimization approach will be presented.