A Novel Circularly Polarised Butterfly RF Coil Concept for MRI

Magnetic resonance imaging (MRI) is an invaluable tool for the diagnosis and study of brain function. Central to the MRI system, the radio frequency (RF) coil plays a dual role: stimulating spins and receiving the MR signal, enabling the generation of detailed images from inside the body. Compared to using linear polarised (LP) methods, the efficiency of the RF coil can be improved by leveraging circular polarised (CP) driving methods, which operate with at least two elements and 90° phase input difference. Coil efficiency can also be improved with the use of a multi-channel phased array receive-only coils, as they provide higher SNR compared to volume coils. Generally, all elements of phased array coils operate in LP mode. However, if the LP elements are replaced by dimension-matched CP elements, the SNR of the phased array coil can be further increased. This study introduces a novel single-channel butterfly coil uniquely capable of operating in CP mode. This is achieved by operating the CP element with asymmetrical tuning and a split resonance peak. The performance of the single-channel CP butterfly coil was evaluated in simulations and MR measurements, and the results were compared to those from single-channel LP coils. The results show that the single-channel CP butterfly coil is a good solution for increasing SNR in phased array receive-only coils.