Design and Optimization of a Ring-Pair Permanent Magnet Array for Head Imaging in a Low-Field Portable MRI System

In this paper, we present the design and optimization of a ring-pair permanent magnet array for head imaging in a low-held portable magnetic resonance imaging (MRI) system. The proposed array generates a longitudinal main static magnetic held (B0held) with an average held strength of 169.7 mT and a homogeneity of 24786 ppm in a held of view with a diameter of 200 mm and a thickness of 50 mm. It is a signihcant increase in held homogeneity by 79.7% compared to a traditional ring-pair structure of the same dimension and mass while still maintaining a similar held strength. The optimization was implemented by applying a genetic algorithm and by proposing an efhcient current model for the forward calculation of the magnetic held. The effectiveness of the optimization is validated by realistic simulations using COMSOL Multiphysics. Compared to a Halbach array, where the held is transversal and the existing coil designs cannot be applied directly, the proposed array generates stronger helds. Its magnetic held is longitudinal, which allows the direct application of the advancements in RF coil designs in a conventional MRI system to the imaging system using the proposed magnet array.