Construction and Evaluation of a Switch-Tuned 13C - 1H Birdcage Radiofrequency Coil for Imaging the Metabolism of Hyperpolarized 13C-Enriched Compounds

Purpose: To construct a switch-tuned C-13 - H-1 birdcage radiofrequency (RF) coil system capable of metabolic imaging of hyperpolarized C-13-enriched metabolic probes for co-registration with MRI morphology using protons. Materials and Methods: The switch-tuned coil was constructed using PIN diodes for rapid switching of the resonant frequency of the coil. Identical, single-tuned, H-1 and C-13 birdcage RF coils have also been constructed for comparison of imaging performance. A C-13 receive-only surface RF coil has been integrated with the switch-tuned coil for transmit-only, receive-only operation (TORO) to increase local C-13 signal for improved signal-to-noise ratio (SNR). Results: The SNR achieved with the switch-tuned coil in transmit/receive mode was 87% that of the single-tuned H-1 coil. For C-13 imaging, the SNR for the switch-tuned coil was 55% that of the single-tuned C-13 coil. TORO operation of the switch-tuned coil with the surface coil increased SNR for by a factor of 4.2 over transmit/receive operation of the switch-tuned coil alone. Conclusion: A surface coil can be integrated with a switch-tuned C-13 - H-1 coil for C-13 TORO operation producing improved SNR. In vivo metabolic imaging of [1-C-13]pyruvate in a rat model of glioma is demonstrated using TORO operation, which is co-registered with H-1-imaged anatomy.