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

To develop a double-tuned calf coil with excellent ¹H and ³¹P performance to study muscle physiology by interleaved ¹H/³¹P MRS and parallel imaging at 7 T.

The coil combines three ¹H transceive dipoles, six ¹H receive-only loops and three ³¹P transceive loops, arranged in a nested, half-cylindrical layout. Several different decoupling mechanisms were implemented to limit electromagnetic interactions within the ¹H and ³¹P arrays, between transmit and receive elements as well as ¹H-³¹P cross-coupling. A custom housing was designed for mechanical stability and ease of use. The ¹H and ³¹P performance were investigated on phantoms and demonstrated in vivo in an exemplary measurement with interleaved, localized ¹H/³¹P MRS in the gastrocnemius muscle of a healthy subject at rest, during exercise and recovery.

On phantoms, compared to a double-tuned reference coil, the new coil showed 2.8-fold higher ¹H SNR, a stronger and more homogenous ¹H transmit field, and 27% lower ³¹P SNR. It enabled four-fold GRAPPA acceleration. In vivo the CH₂ resonance of creatine and PCr were fitted from the unaveraged ¹H and ³¹P spectra, which resulted in time courses with closely matching depletion and recovery constants.

These results highlight the coil's suitability for the target application of advanced metabolic calf muscle studies. Its high ¹H performance will enable ¹H 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.