A Novel Active Shim Coil Design Scheme for the Effective Imaging Region above the Patient Bed in MRI

In this paper, a novel active shim coil design scheme is proposed. In MRI, active shim coils are typically designed to correct the magnetic field inhomogeneity within the imaging region defined as the diameter of spherical volume (DSV). In general, the fields in the space under the patient bed are not used during MRI scanning; however, they are still considered in the shim coil design. Here, a new design scheme is proposed that only shims the effective fields above the patient’s bed. Meanwhile, the shim coils are designed to wind onto a novel D-shaped geometric former, which comprises an upper cylindrical structure and a lower planar structure. In the simulation study, the shim coils are designed by a boundary element method (BEM). Compared with the conventional cylindrical designs, the new solution could significantly improve the electromagnetic performances of the shim coils. With similar coil efficiency, the resistance and inductance of the new coils are decreased by 6.4 ~ 19.6% and 10.7 ~ 28.1%, respectively.