Creating a clinical platform for carbon‐13 studies using the sodium‐23 and proton resonances

PURPOSE: Calibration of hyperpolarized (13)C‐MRI is limited by the low signal from endogenous carbon‐containing molecules and consequently requires (13)C‐enriched external phantoms. This study investigated the feasibility of using either (23)Na‐MRI or (1)H‐MRI to calibrate the (13)C excitation. METHODS: Commercial (13)C‐coils were used to estimate the transmit gain and center frequency for (13)C and (23)Na resonances. Simulations of the transmit B (1) profile of a Helmholtz loop were performed. Noise correlation was measured for both nuclei. A retrospective analysis of human data assessing the use of the (1)H resonance to predict [1‐(13)C]pyruvate center frequency was also performed. In vivo experiments were undertaken in the lower limbs of 6 pigs following injection of hyperpolarized (13)C‐pyruvate. RESULTS: The difference in center frequencies and transmit gain between tissue (23)Na and [1‐(13)C]pyruvate was reproducible, with a mean scale factor of 1.05179 ± 0.00001 and 10.4 ± 0.2 dB, respectively. Utilizing the (1)H water peak, it was possible to retrospectively predict the (13)C‐pyruvate center frequency with a standard deviation of only 11 Hz sufficient for spectral–spatial excitation‐based studies. CONCLUSION: We demonstrate the feasibility of using the (23)Na and (1)H resonances to calibrate the (13)C transmit B (1) using commercially available (13)C‐coils. The method provides a simple approach for in vivo calibration and could improve clinical workflow.