On the spin order transfer from parahydrogen to another nucleus

Abstract

The hyperpolarization of nuclear spins holds great potential e.g. for biomedical research. Strong signal enhancements have been demonstrated e.g. by transforming the spin order of parahydrogen (pH2) to net polarization of a third nucleus (e.g. 13C) by means of a spin-order-transfer (SOT) sequence. The polarization achieved is vitally dependent on the sequence intervals, which are a function of the J-coupling constants of the molecule to be polarized. How to derive the SOT sequence intervals, the actual values for molecules as well as the (theoretical) polarization yield and robustness, however, are not fully described. In this paper, (a) we provide the methods to obtain the SOT intervals for a given set of J-coupling constants (i.e. of a new hyperpolarization agent); (b) exemplify these methods on molecules from literature, providing the hitherto missing intervals and simulated polarization yield; and (c) assess the robustness of the sequences towards B1 and J-coupling errors. Close to unity polarization is obtained for all molecules and sequences. Furthermore, the loss of polarization caused by erroneous B1 and J-coupling constants is reduced by choosing the channel and phase of some pulses in the SOT sequences appropriately.