Multimodal concentric surface coils for enhanced sensitivity in MR imaging

Abstract: This study presents the design, simulation, and experimental validation of a novel multimodal concentric surface coil for MR imaging, developed to achieve higher B1 field efficiency while maintaining low SAR for enhanced imaging performance. The coil comprises multiple electromagnetically coupled concentric resonators of varying sizes. The resonant frequency of a desired mode is tuned to 127 MHz, as an example, to demonstrate the performance of the proposed technique at 3 Tesla. Fullwave electromagnetic simulations of the proposed design and bench tests of fabricated prototypes were conducted to evaluate the coil's B1 field efficiency and distribution, multimodal resonance behavior, scattering parameters, and SAR performance. Inductive Current Elimination or magnetic wall decoupling was implemented to enhance channel isolation in a multi channel configuration to demonstrate the feasibility of applying this multimodal technique to RF array design and parallel imaging. Experimental results show that the proposed concentric coil achieves higher B1 field efficiency and reduced SAR compared to a conventional surface coil of the same size operating at 3 Tesla. Bench measurements on the prototypes confirmed successful tuning and impedance matching, with measured S11 and S21 parameters validating the effectiveness of the decoupling strategy. B1 mapping experiments further demonstrated efficient RF power delivery across multiple planes. These findings suggest that the proposed multimodal concentric coil has the potential to serve as a promising alternative to conventional surface coils for high performance MR imaging, offering enhanced RF efficiency, reduced SAR, and the ability to construct multichannel RF arrays.