PHIP hyperpolarized [1-C]pyruvate and [1-C]acetate esters via PH-INEPT polarization transfer monitored by C NMR and MRI.

Parahydrogen-induced polarization of C nuclei by side-arm hydrogenation (PHIP-SAH) for [1-C]acetate and [1-C]pyruvate esters with application of PH-INEPT-type pulse sequences for H to C polarization transfer is reported, and its efficiency is compared with that of polarization transfer based on magnetic field cycling (MFC). The pulse-sequence transfer approach may have its merits in some applications because the entire hyperpolarization procedure is implemented directly in an NMR or MRI instrument, whereas MFC requires a controlled field variation at low magnetic fields. Optimization of the PH-INEPT-type transfer sequences resulted in C polarization values of 0.66 ± 0.04% and 0.19 ± 0.02% for allyl [1-C]pyruvate and ethyl [1-C]acetate, respectively, which is lower than the corresponding polarization levels obtained with MFC for H to C polarization transfer (3.95 ± 0.05% and 0.65 ± 0.05% for allyl [1-C]pyruvate and ethyl [1-C]acetate, respectively). Nevertheless, a significant C NMR signal enhancement with respect to thermal polarization allowed us to perform C MR imaging of both biologically relevant hyperpolarized molecules which can be used to produce useful contrast agents for the in vivo imaging applications.