High spatiotemporal resolution bSSFP imaging of hyperpolarized [1-¹³C]pyruvate and [1-¹³C]lactate with spectral suppression of alanine and pyruvate-hydrate

Purpose: The balanced steady-state free precession (bSSFP) acquisition enables high spatiotemporal resolution for hyperpolarized ¹³C MRI at 3T but is limited by spectral contamination from adjacent resonances. The purpose of this study was to develop a framework for in vivo dynamic high resolution imaging of hyperpolarized [1-¹³C]pyruvate and [1-¹³C]lactate generated in vivo at 3T by simplifying the spectrum through the use of selective suppression pulses. Methods: Spectral suppression pulses were incorporated into the bSSFP sequence for suppression of [1-¹³C]alanine and [1-¹³C]pyruvate-hydrate signals, leaving only the pyruvate and lactate resonances. Subsequently, the bSSFP pulse width, time-bandwidth, and repetition time were optimized for imaging these dual resonances. Results: The spectral suppression reduced both the alanine and pyruvate-hydrate signals by 85.5 ± 4.9% and had no significant effect on quantitation of pyruvate to lactate conversion (liver: P = 0.400, kidney: P = 0.499). High resolution (2 × 2 mm² and 3 × 3 mm²) subsecond 2D coronal projections and 3D 2.5 mm isotropic images were obtained in rats and tumor-bearing mice with 1.8–5 s temporal resolution, allowing for calculation of lactate-to-pyruvate ratios and k_PL. Conclusion: The developed framework presented here shows the capability for dynamic high resolution volumetric hyperpolarized bSSFP imaging of pyruvate-to-lactate conversion on a clinical 3T MR scanner.