Fast analytical calculation method for eddy current induced by gradient fields in an MRI system

Abstract

Purpose Eddy currents are inevitable in magnetic resonance imaging (MRI) systems. These currents are mainly induced by gradient fields. This study aims to propose a fast analytical method to calculate eddy currents induced by frequently switching gradient fields in a traditional C-shape MRI system. Design/methodology/approach Fourier decomposition and magnetic vector potentials were used to calculate the eddy currents. Calculations with the proposed analytical method revealed the spatial distribution and temporal evolution of eddy currents. Findings Calculation and Maxwell simulation results were consistent. The agreement between calculation and simulation results indicates that increasingly sophisticated structures could be developed. The calculated results could guide the design of improved gradient coils. Originality/value Eddy currents induced by gradient current are decomposed into currents induced by each time-harmonic component, and then adding them together to obtain complete contribution of the eddy current. The analytical method was used to characterize the properties of symmetric and asymmetric eddy currents induced by gradient coils in MRI systems. The analytical method can be used to improve the gradient shield during the design of the gradient coil in the MRI system.

Design and test of an open portable MRI system

“…The gradient coils generate a high-frequency magnetic field. This field variation induces eddy currents in the solid conductive parts (magnets and iron) which can affect the gradient field (Xu et al , 2017). In addition, these eddy currents can also result in heat generation in the magnets and the iron.…”