Dynamic 13C-1H nuclear polarization of lipid methylene resonances applied to broadband proton-decoupled in vivo 13C MR spectroscopy of human breast and calf tissue.

Dynamic nuclear polarization of the coupled 13C-1H spin system was studied for optimizing the signal-to-noise ratio of in vivo 13C MR spectra. In particular, the truncated driven and transient nuclear Overhauser effect (NOE) of the proton-decoupled 13C resonances from methylene carbons in vegetable oil and in human calf tissue was observed. Maximum in vivo NOE enhancements eta = 1.5 and 0.9 were found, respectively. Theoretical fits to the data yield 13C-1H cross-relaxation times in the order of 0.6 s. Significant signal enhancement over the whole in vivo 13C chemical shift range is obtained with minimum expense utilizing the NOE of the dipolar coupled 13C-1H spin system in addition to proton-decoupling. NOE-enhanced proton-decoupled in vivo 13C MR spectra were acquired within 17 min in volunteer examinations from the human breast and the calf. These spectra show well-resolved resonances of carbons in lipids and several other cellular compounds.