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

Abstract

Purpose: Calibration of hyperpolarized 13C-MRI is limited by the low signal from endogenous carbon-containing molecules and consequently requires 13C-enriched external phantoms. This study investigated the feasibility of using either 23Na-MRI or 1H-MRI to calibrate the 13C excitation. Methods: Commercial 13C-coils were used to estimate the transmit gain and center frequency for 13C and 23Na resonances. Simulations of the transmit B1 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 1H resonance to predict [1-13C]pyruvate center frequency was also performed. In vivo experiments were undertaken in the lower limbs of 6 pigs following injection of hyperpolarized 13C-pyruvate. Results: The difference in center frequencies and transmit gain between tissue 23Na and [1-13C]pyruvate was reproducible, with a mean scale factor of 1.05179 ± 0.00001 and 10.4 ± 0.2 dB, respectively. Utilizing the 1H water peak, it was possible to retrospectively predict the 13C-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 23Na and 1H resonances to calibrate the 13C transmit B1 using commercially available 13C-coils. The method provides a simple approach for in vivo calibration and could improve clinical workflow.