کنفرانس مهندسی برق ایران

صفحه اصلی / سی و چهارمین کنفرانس بین المللی مهندسی برق

Optimization of a Halbach array magnet for a low field MRI system Using a Multi-objective Genetic Algorithm

نویسندگان :

Fatemeh Alirezaee¹ Mohammad Mohammadzadeh² Mohammad Amin Khanpour³

1- دانشگاه شهید بهشتی تهران 2- دانشگاه شهیدبهشتی تهران 3- دانشگاه شهیدبهشتی تهران

کلمات کلیدی :

Low field MRI system،Halbach Array Magnet،Permanent Magnet Optimization،Homogeneous magnetic field،Genetic algorithm (GA)

چکیده :

Low-field MRI systems increasingly rely on Halbach array magnets. Practical realizations of a Halbach array, with finite length and discrete magnets, suffer from severe magnetic field inhomogeneity. In this project, we present the optimization of a 36-cm-bore Halbach array dedicated for adult head imaging, using a genetic algorithm (GA). First, several analytical methods for calculating the magnetic field of cubic permanent magnets are evaluated and benchmarked against finite-element simulations performed in COMSOL Multiphysics. Subsequently, two GA-based optimization approaches are investigated within a 20-cm diameter spherical volume (DSV). In the first approach, the objective function targets the homogeneity of the transverse magnetic field component (B_y), resulting in a configuration with 11,750 ppm B_y inhomogeneity and 10,430 ppm magnetic field magnitude (|B|) inhomogeneity. In the second approach, the optimization objective is the homogeneity of (|B|), yielding an improved |B| inhomogeneity of 9,780 ppm; however, this configuration exhibits degraded transverse field homogeneity (10,850 ppm) and a 40% increase in the average magnitude of orthogonal (unwanted) field components. These results show that, at some points in DSV, a reduction in B_y, can be partially compensated by increased orthogonal components, producing a seemingly more homogeneous |B| field. Nevertheless, such compensation degrades the effective transverse magnetization and reduces free induction decay (FID) signal. This study highlights that, particularly for low-aspect-ratio Halbach arrays, an accurate optimization requires simultaneous consideration of all three magnetic field components to ensure true field homogeneity.