Designing High-Permittivity Pads for Dielectric Shimming in MRI using Model Order Reduction and Gauss-Newton Optimization

Abstract

High-field MRI reduces the homogeneity of the B1+ transmit field, which in turn degrades the quality of MR images. High-permittivity pads are increasingly used to restore the homogeneity of this transmit field. Designing such a pad in terms of dimensions, position, and constitution is not trivial, however, and in this work we propose a design method that can be used to find an optimal pad for a certain imaging region of interest. By incorporating a projection based model order reduction technique in a Gauss-Newton optimization method, optimal dielectric pads can be found at significantly reduced computation times. We illustrate the performance of our optimization method by designing a pad for 7T cerebellum imaging and show its effectiveness in an actual MR imaging experiment.