Design simulation of high-homogeneity portable MRI magnet array using global optimization algorithm and equivalent currents model

Background

High-field magnetic resonance imaging (MRI) systems offer high sensitivity and resolution but are costly and bulky, limiting their widespread use, particularly in remote areas. Conversely, portable MRI systems have emerged as a complementary technology, promising enhanced accessibility.

Purpose

This study introduces a novel optimization method combining an analytical model with a highly convergent global optimization algorithm to enhance the design of portable MRI permanent magnet arrays. The approach aims to significantly improve the efficiency of the magnet design process, thereby advancing the homogeneity of portable MRI magnet array.

Methods

The proposed approach begins with the calculation of initial magnetic field distributions using current element principles. This is followed by the development of an advanced analytical model based on matrix algebra. The consistency between the calculated results of the analytical model and the results from finite element method (FEM) simulations is then evaluated to assess the reliability of the magnetic field calculations across various magnet array configurations. The integration of the analytical model with the improved grey wolf optimization (IGWO) algorithm enhances the optimization process, leading to magnet array configurations with improved homogeneity.

Results

FEM simulations agree with the analytical model, revealing a computational error with an average root mean square error (RMSE) of 0.4% in the magnetic field map. The calculation speed of analytical model is at least 200 times higher than that using FEM-based software with uncompromised accuracy. The optimization process successfully yields a permanent magnet array with exceptional homogeneity (1080 ppm) and strong field strength (79.5 mT) across a 0.2 m diameter of spherical volume (DSV). Moreover, this is accomplished while maintaining a lightweight (129 kg) and compact design (interior diameter: 0.31 m). The IGWO model has been shown to outperform the benchmark genetic algorithm (GA) model, which is currently used for magnet design in MRI.

Conclusions

This study introduces a novel optimization method that significantly enhances the design of portable MRI permanent magnet arrays. By integrating an analytical model with the IGWO algorithm, this method enhances the efficiency of magnet design compared to traditional FEM. This method addresses the limitations of traditional magnet optimization techniques, which are often susceptible to local optima. The results indicate that this method can play a crucial role in developing MRI systems with high homogeneity.