Toward 13C hyperpolarized biomarkers produced by thermal mixing with hyperpolarized 129Xe

The C-13 NMR signal of acetic acid 1-C-13-AcH is enhanced by polarization transfer from hyperpolarized Xe-129 using a thermal mixing procedure. 1-C-13-AcH acid and hyperpolarized Xe-129 are mixed as gases to disperse Xe-129 in the acetic acid. The mixture is frozen with liquid N-2 at 0.5 T. The magnetic field is then momentarily dropped to allow for exchange of spin polarization between C-13 and Xe-129. After polarization exchange the magnetic field is raised to its original value and the mixture is thawed, resulting in a solution of polarization enhanced 1-C-13-AcH. A C-13 nuclear spin polarization enhancement of 10 is observed compared to its thermal polarization at 4.7 T. This polarization enhancement is approximately three orders of magnitude lower than that predicted by theory. The discrepancy is attributed to the formation of either an inhomogeneous solid matrix and/or spin dynamics during polarization transfer. Despite the low polarization enhancement, this is the first report of polarization transfer from Xe-129 to C-13 nuclear spins achieved by thermal mixing for a proton-containing molecule of biomedical importance. If future work can increase the enhancement, this method will be useful in hyperpolarizing a wide range of C-13 enriched compounds important in biomedical and biophysical research.