UCSF

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 J_CH  = ∼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 80:36-41, 2018. © 2017 International Society for Magnetic Resonance in Medicine.