Research on MRI Gradient Coil Magnetic Field Induced Eddy Current Method

Abstract

After the production of the gradient coil of the magnetic resonance imaging system, electromagnetic field testing is required to verify whether the assembly accuracy meets the electromagnetic field requirements. Since the passive magnetic field Bz satisfies the Laplace,s equation and is a harmonic function, and according to the extreme value principle of harmonic function, the maximum or minimum values of Bz can only appear on the boundaries, so the observation points of the magnetic field are generally selected on the surface of the spherical imaging area. For superconducting magnets used for human body magnetic resonance imaging, a spherical area with a center diameter of 40~50 cm is generally selected as the shimming target area. Only the field value of the target area needs to be measured, and the spherical harmonic coefficients obtained after data processing are used to determine the magnetic field performance of the gradient coil. There are many testing principles and methods for electromagnetic fields, so there is no unified way and method in the field of commercial applications. This article is based on the Gauss-Legendre numerical integration, measures and analyzes the magnetic field performance of gradient coils by building a data acquisition system, and this article applies numerical analysis methods to calculate the spherical harmonic coefficients of the magnetic field using discrete test data, providing a feasible method for the production and testing of gradient coils.

Keywords

• gradient coil
• spherical harmonic coefficient
• gauss-legendre numerical integration
• magnetic resonance imaging (mri) system