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

Abstract

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 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 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 B₁ using commercially available ¹³ C-coils. The method provides a simple approach for in vivo calibration and could improve clinical workflow.

Keywords: MRI; calibration; carbon-13; hyperpolarized; sodium-23.