A Novel 9‐Channel 1 H , 3‐Channel 31 P Radiofrequency Coil for Interleaved Multinuclear Studies of Human Calf Muscle at 7 T

ABSTRACT Purpose To develop a double‐tuned calf coil with excellent 1 H and 31 P performance to study muscle physiology by interleaved 1 H/ 31 P MRS and parallel imaging at 7 T. Methods The coil combines three 1 H transceive dipoles, six 1 H receive‐only loops and three 31 P transceive loops, arranged in a nested, half‐cylindrical layout. Several different decoupling mechanisms were implemented to limit electromagnetic interactions within the 1 H and 31 P arrays, between transmit and receive elements as well as 1 H‐ 31 P cross‐coupling. A custom housing was designed for mechanical stability and ease of use. The 1 H and 31 P performance were investigated on phantoms and demonstrated in vivo in an exemplary measurement with interleaved, localized 1 H/ 31 P MRS in the gastrocnemius muscle of a healthy subject at rest, during exercise and recovery. Results On phantoms, compared to a double‐tuned reference coil, the new coil showed 2.8‐fold higher 1 H SNR, a stronger and more homogenous 1 H transmit field, and 27% lower 31 P SNR. It enabled four‐fold GRAPPA acceleration. In vivo the CH 2 resonance of creatine and PCr were fitted from the unaveraged 1 H and 31 P spectra, which resulted in time courses with closely matching depletion and recovery constants. Conclusion These results highlight the coil's suitability for the target application of advanced metabolic calf muscle studies. Its high 1 H performance will enable 1 H MRS acquisitions with improved spatial and temporal resolution and enable the implementation of MRS sequences that had previously been limited by insufficient SNR, which will generate new insights into muscle physiology.