Microstrip-Line Characterization of Artificial Dielectric Materials for MRI Applications

Abstract

Artificial dielectric materials (ADMs) offer a flexible means of shaping radiofrequency fields in magnetic resonance imaging (MRI). However, ADM designs based on plane-wave characterization may not directly predict their effects on RF fields in MRI. We propose a travelling-wave microstrip-line (MSL) approach to approximate the spatially nonuniform excitation experienced by dielectric pads near MRI RF coils and to guide ADM characterization and tuning against a reference dielectric. Both materials are tested under identical MSL measurement conditions, and the ADM geometry is adjusted until its reflection minimum occurs at the same frequency as that of the reference. Simulations and bench measurements show that the tuned ADM more closely matches the reference dielectric's reflection-minimum frequency than a plane-wave-based design. MRI simulations show that the tuned ADM produces a transmit magnetic-field distribution similar to that of the reference pad. Phantom images acquired at 7 T also show similar image-intensity patterns. These results demonstrate the utility of MSL response matching for guiding ADM design in the tested configuration. The proposed approach provides a practical bench-top step for assessing and tuning manufactured ADMs before MRI evaluation.