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

ABSTRACT

PURPOSE: Although 1 H spin coupling is generally avoided in probes for hyperpolarized (HP) 13 C MRI, enzymatic transformations of biological interest can introduce large 13 C-1 H couplings in vivo. The purpose of this study was to develop and investigate the application of 1 H decoupling for enhancing the sensitivity for detection of affected HP 13 C metabolic products. METHODS: A standalone 1 H decoupler system and custom concentric 13 C/1 H paddle coil setup were integrated with a clinical 3T MRI scanner for in vivo 13 C MR studies using HP [2-13 C]dihydroxyacetone, a novel sensor of hepatic energy status. Major 13 C-1 H coupling JCH = ∼150 Hz) is introduced after adenosine triphosphate-dependent enzymatic transformation of HP [2-13 C]dihydroxyacetone to [2-13 C]glycerol-3-phosphate in vivo. Application of WALTZ-16 1 H decoupling for elimination of large 13 C-1 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, 1 H-decoupled 13 C MR of thermally polarized glycerol and the HP metabolic product [2-13 C]glycerol-3-phosphate was achieved at forward power of approximately 15 W. High-quality 3-s dynamic in vivo HP 13 C MR scans were acquired with decoupling duty cycle of 5%. Application of 1 H decoupling resulted in sensitivity enhancement of 1.7-fold for detection of metabolic conversion of [2-13 C]dihydroxyacetone to HP [2-13 C]glycerol-3-phosphate in vivo. CONCLUSIONS: Application of 1 H decoupling provides significant sensitivity enhancement for detection of HP 13 C metabolic products with large 1 H spin couplings, and is therefore expected to be useful for preclinical and potentially clinical HP 13 C MR studies. Magn Reson Med 8036-41, 2018. © 2017 International Society for Magnetic Resonance in Medicine.