Optimization of Coil Element Configurations Based on Matrix Gradient Coil

Abstract

Matrix gradient coils (also named multi-coils or arrays) have been introduced for magnetic resonance imaging (MRI) and shimming with amount of coil elements. However, equipping each coil element with a power amplifier is not always convenient because of expensive cost and complex control system. This study aims to analyze the effect of coil elements on generating magnetic fields and reduce the number of amplifiers, which is fewer than the number of coil elements for similar system performance, low cost, and simple control of matrix gradient coil system. A matrix gradient coil with 48-channels is created to generate the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$X$ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Y$ </tex-math></inline-formula> , and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Z$ </tex-math></inline-formula> gradient magnetic fields, respectively. The metric role of coil element is implemented, and the relationship between the distribution of coil elements and the target fields is analyzed. Eliminating the coil elements that have no effect on the target field and connecting the coil elements that have the same amplitude of current in series, the coil element configurations are obtained. Different configurations have different groups and coil elements in the same group are driven via an amplifier. Three power amplifiers are sufficient to generate the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$X$ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Y$ </tex-math></inline-formula> , and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Z$ </tex-math></inline-formula> gradient fields, respectively, in this study. Comparing the results of using full 48 amplifiers and using three amplifiers, the performances of the coil system for producing the magnetic fields are similar. Experiments for generating all linear gradient fields demonstrate that using fewer amplifiers to drive coil elements can also achieve acceptable results. The optimization method for configurating the coil elements is simple and time-saving to reduce the number of amplifiers to drive the matrix gradient coil.