PHIP hyperpolarized [1-13C]pyruvate and [1-13C]acetate esters via PH-INEPT polarization transfer monitored by 13C NMR and MRI
Alexandra Svyatova, Vitaly P. Kozinenko, Nikita V. Chukanov, Dudari B. Burueva, Eduard Y. Chekmenev, Yuwen Chen, Dennis W. Hwang, Kirill V. Kovtunov, Igor V. Koptyug
Abstract
Abstract Parahydrogen-induced polarization of 13 C nuclei by side-arm hydrogenation (PHIP-SAH) for [1- 13 C]acetate and [1- 13 C]pyruvate esters with application of PH-INEPT-type pulse sequences for 1 H to 13 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 13 C polarization values of 0.66 ± 0.04% and 0.19 ± 0.02% for allyl [1- 13 C]pyruvate and ethyl [1- 13 C]acetate, respectively, which is lower than the corresponding polarization levels obtained with MFC for 1 H to 13 C polarization transfer (3.95 ± 0.05% and 0.65 ± 0.05% for allyl [1- 13 C]pyruvate and ethyl [1- 13 C]acetate, respectively). Nevertheless, a significant 13 C NMR signal enhancement with respect to thermal polarization allowed us to perform 13 C MR imaging of both biologically relevant hyperpolarized molecules which can be used to produce useful contrast agents for the in vivo imaging applications.