Relayed magnetization transfer from nuclear Overhauser effect and chemical exchange observed by in vivo 31P MRS in rat brain

The P-31 magnetization transfer effects among nuclear magnetic resonances (NMRs) of phosphocreatine (PCr), gamma-adenosine-5'-triphosphate (gamma-ATP) and inorganic phosphate (Pi) have been attributed to the chemical exchange reactions among PCr, ATP and Pi catalyzed by creatine kinase (CK) and ATPase enzymes and, therefore, are commonly applied in situ to measure chemical exchange fluxes involving two chemically coupled CK and ATPase reactions (i.e., PCr <-> ATP <-> Pi) by selectively saturating gamma-ATP resonance. Besides the expected reductions in the Pi and PCr NMR signals upon saturating gamma-ATP resonance, one particularly interesting phenomenon showing decreases in alpha-ATP and beta-ATP signals was also observed. The underlying mechanism was investigated and identified via saturating NMR of beta-ATP in the present study. The unique relayed magnetization transfer effects through spin diffusion were observed in the rat brain using in vivo P-31 magnetic resonance spectroscopy. (C) 2012 Elsevier Inc. All rights reserved.