Numerical Design of High-Efficiency Whole-Body Gradient Coils With a Hybrid Cylindrical-Planar Structure

In this paper, a set of novel whole-body gradient coils is designed for cylindrical magnetic resonance imaging (MRI) systems. For the sake of high coil efficiency, the design scheme focuses on the imaging volume occupied by the patient, discounting the large space under the patient bed that is unused during imaging. To further improve the coil performance, the coils are designed on an unconventional, hybrid cylindrical-planar structure, where the primary coils are arranged on a chord-truncated cylindrical former while the shielding coils remain on the cylindrical assemblies. In this new coil configuration, the primary layers make the best possible use of the space closest to the imaging volume, whilst the shielding layers are positioned the furthest from the primary layers; thus, the best gradient field/current ratio can be obtained for the body coil configuration. Using a boundary element method, a full gradient set was designed to demonstrate the effectiveness of the proposed scheme. Compared with conventional designs, the new approach provides significantly improved coil performance. For the three gradient axes, the inductance was reduced by 25%-50%, the resistance was decreased by 19%-39%, and the minimum wire distance was increased by 5.2%-45.5%. In terms of shielding effect, the maximum stray fields of the X- and Y-gradient coils are reduced by 79.5% and 38.7%, respectively. It is concluded that the new design is capable of producing high-quality gradients with less eddy currents and thermal heating concerns, being suitable for MRI applications demanding a high gradient performance.