Dynamic 13C−1H nuclear polarization of lipid methylene resonances applied to broadband proton‐decoupled in vivo13C MR spectroscopy of human breast and calf tissue

Abstract

Dynamic nuclear polarization of the coupled ¹³C−^lH spin system was studied for optimizing the signal‐to‐noise ratio of in vivo¹³C 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 n = 1.5 and 0.9 were found, respectively. Theoretical fits to the data yield ¹³C−¹ cross‐relaxation times in the order of 0.6 s. Significant signal enhancement over the whole in vivo¹³C chemical shift range is obtained with minimum expense utilizing the NOE of the dipolar coupled ¹³C−¹ spin system in addition to proton‐decoupling. NOE‐enhanced proton‐decoupled in vivo¹³C 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.