Compact MR Magnet Design Methodology for Superconducting Animal MRI Scanner

Abstract

A 4.7 T compact superconducting magnet system for active shielding animal magnetic resonance imaging scanner was designed in this work. The resulting magnet consists of nine coaxial coils symmetrical about the z -axis. The innermost main coils and outermost shielding coils were made up of six inner coils with the positive current direction and three outer coils with the negative current direction, respectively. These nine superconducting coils contribute their efforts together to produce a 4.7 T main background magnetic field, and the peak-to-peak field homogeneity was 2 ppm over a 20 cm region of interest (ROI). The diameter of room temperature bore was 400 mm, which is large enough for most animals imaging, and five Gauss fringe field is restricted within an elliptical region with the size of 1.5 m in radial and 2.2 m in axial direction, much smaller than the regular requirement 2.5 m and 4.0 m, respectively. A hybrid numerical methodology that combined linear programming and nonlinear optimization algorithm for actively shielding homogeneous superconducting magnet was proposed here. From the simulation results, we can see that the homogeneity over ROI and limitation to the five Gauss fringe field can be well controlled, and so does the maximum electromagnetic stress.