An Efficient Methodology for the Analysis of Dielectric Shimming Materials in Magnetic Resonance Imaging

Interference effects in the transmit <inline-formula> <tex-math notation="LaTeX">$B_{1}^{+}$ </tex-math></inline-formula> field can severely degrade the image quality in high-field Magnetic Resonance Imaging (MRI). High-permittivity pads are increasingly used to counteract these effects, but designing such pads is not trivial. In this paper, we present an efficient solution methodology for this dielectric RF shimming problem. By exploiting the fact that dielectric pads form a low rank perturbation of a large-scale background model, we are able to efficiently compute <inline-formula> <tex-math notation="LaTeX">$B_{1}^{+}$ </tex-math></inline-formula> fields that correspond to a wide range of different pad realizations. This allows us to efficiently design dielectric pads that eliminate the <inline-formula> <tex-math notation="LaTeX">$B_{1}^{+}$ </tex-math></inline-formula>-interference effects of high-field MRI. We show that significant speed up factors can be achieved compared with traditional field simulation approaches and we validate our approach against measurements. Measured and simulated field responses are in good agreement with each other indicating that the proposed solution methodology enables us to efficiently analyze dielectric pads in realistic MRI measurement settings.