Z-Gradient Coil Design with Improved Anti-eddy Performance for MRI System with Opposed Permanent Magnets

This study introduces a method for designing the Z-gradient coil in a low-field (0.05 T) magnetic resonance imaging (MRI) system, taking into consideration the adverse effects of Z-gradient coil-induced eddy currents (gradient eddy currents). The gradient coil with a better anti-eddy performance means that it produces smaller eddy currents in the surrounding structures and thus has a smaller impact on imaging results. The electromagnetic complexity of the device makes it challenging to evaluate the impact of Z-gradient coil-induced eddy currents. To address this issue, a simplified two-dimensional model based on the finite-element method (FEM) is proposed. A multi-objective optimization method is approximately solved to get the Pareto front, considering nonlinearity, gradient efficiency, and inductance. The simulated field response and eddy losses serve as the final evaluation factors to ensure that the good anti-eddy performance. The fabricated optimal Z-gradient coil is tested and compared with a coil designed from the conventional method. Experimental eddy current response and T2-weighted image comparison show that the optimal coil has better anti-eddy performance than the conventional coil.