Sensitivity enhancement for detection of hyperpolarized ¹³C MRI probes with ¹H spin coupling introduced by enzymatic transformation in vivo

Purpose: Although ¹H spin coupling is generally avoided in probes for hyperpolarized (HP) ¹³C MRI, enzymatic transformations of biological interest can introduce large ¹³C-¹H couplings in vivo. The purpose of this study was to develop and investigate the application of ¹H decoupling for enhancing the sensitivity for detection of affected HP ¹³C metabolic products. Methods: A standalone ¹H decoupler system and custom concentric ¹³C/¹H paddle coil setup were integrated with a clinical 3T MRI scanner for in vivo ¹³C MR studies using HP [2-¹³C]dihydroxyacetone, a novel sensor of hepatic energy status. Major ¹³C-¹H coupling J_CH = ∼150 Hz) is introduced after adenosine triphosphate–dependent enzymatic transformation of HP [2-¹³C]dihydroxyacetone to [2-¹³C]glycerol-3-phosphate in vivo. Application of WALTZ-16 ¹H decoupling for elimination of large ¹³C-¹H couplings was first tested in thermally polarized glycerol phantoms and then for in vivo HP MR studies in three rats, scanned both with and without decoupling. Results: As configured, ¹H-decoupled ¹³C MR of thermally polarized glycerol and the HP metabolic product [2-¹³C]glycerol-3-phosphate was achieved at forward power of approximately 15 W. High-quality 3-s dynamic in vivo HP ¹³C MR scans were acquired with decoupling duty cycle of 5%. Application of ¹H decoupling resulted in sensitivity enhancement of 1.7-fold for detection of metabolic conversion of [2-¹³C]dihydroxyacetone to HP [2-¹³C]glycerol-3-phosphate in vivo. Conclusions: Application of ¹H decoupling provides significant sensitivity enhancement for detection of HP ¹³C metabolic products with large ¹H spin couplings, and is therefore expected to be useful for preclinical and potentially clinical HP ¹³C MR studies. Magn Reson Med 80:36–41, 2018.