A Novel Magnetic Thermal Stability Index System for Evaluating the Temperature Effects on Magnetic Fields in High-Homogeneity Portable Whole-Body MRI

The stability of magnetic fields under variable temperatures is essential for the effectiveness of portable magnetic resonance imaging (MRI) systems. This research proposes the magnetic thermal stability (MTS) index system, a novel metric to comprehensively evaluate the effects of average temperatures and the temperature range on the average magnetic field strength and magnetic field homogeneity. Employing the improved gray wolf optimization (IGWO) algorithm alongside an analytical model of the Halbach magnet array, a comprehensive whole-body magnet structure model was designed to precisely assess the effects of temperature fluctuations on magnetic field stability. The optimized design achieved an ultra-light whole-body MRI magnet structure with high magnetic field homogeneity of 188 ppm (parts per million) and a total weight of 201 kg. Additionally, extensive analysis of neodymium-ferrite-boron (NdFeB) and samarium-cobalt (SmCo) magnets under varying temperature conditions demonstrated that the temperature range significantly influences magnetic field stability. The drift coefficients of the average magnetic field for NdFeB and SmCo magnets are −1260 and −400 ppm/°C, respectively. Specifically, NdFeB magnets exhibit a homogeneity drift coefficient of 135 ppm/°C, while SmCo magnets demonstrate superior stability with a homogeneity drift coefficient of 40 ppm/°C. Notably, the observed drift coefficient exceeds its inherent temperature coefficient due to additional factors proposed by temperature fluctuations. The MTS index system proves to be a valuable tool for optimizing magnet, critical for deploying MRI in environments with fluctuating temperatures.