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

Purpose: Although H spin coupling is generally avoided in probes for hyperpolarized (HP) C MRI, enzymatic transformations of biological interest can introduce large C- H couplings in vivo. The purpose of this study was to develop and investigate the application of H decoupling for enhancing the sensitivity for detection of affected HP C metabolic products.

Methods: A standalone H decoupler system and custom concentric C/ H paddle coil setup were integrated with a clinical 3T MRI scanner for in vivo C MR studies using HP [2- C]dihydroxyacetone, a novel sensor of hepatic energy status. Major C- H coupling J  = ∼150 Hz) is introduced after adenosine triphosphate-dependent enzymatic transformation of HP [2- C]dihydroxyacetone to [2- C]glycerol-3-phosphate in vivo. Application of WALTZ-16 H decoupling for elimination of large C- H 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, H-decoupled C MR of thermally polarized glycerol and the HP metabolic product [2- C]glycerol-3-phosphate was achieved at forward power of approximately 15 W. High-quality 3-s dynamic in vivo HP C MR scans were acquired with decoupling duty cycle of 5%. Application of H decoupling resulted in sensitivity enhancement of 1.7-fold for detection of metabolic conversion of [2- C]dihydroxyacetone to HP [2- C]glycerol-3-phosphate in vivo.

Conclusions: Application of H decoupling provides significant sensitivity enhancement for detection of HP C metabolic products with large H spin couplings, and is therefore expected to be useful for preclinical and potentially clinical HP C MR studies. Magn Reson Med 80:36-41, 2018. © 2017 International Society for Magnetic Resonance in Medicine.