6 MeV electron irradiated 13C-alanine as a sterile, transportable probe with long-lived radicals for dissolution Dynamic Nuclear Polarization

Motivation: Human hyperpolarized metabolic imaging relies upon unstable exogenous radicals like the trityl radical EPA, necessitating clean rooms, pharmacy staff, and filters. Goal(s): We wished to avoid EPA by using an ultrahigh-dose-rate 6 MeV electron accelerator, generating endogenous [1-13C]alanine radicals for DNP. Approach: We studied irradiated samples up to 100 kGy at two polariser field-strengths (3.35/6.7T), characterised radical species formed by EPR, X-ray diffraction, and numerical quantum-mechanical simulations. Results: Radicals from biologically sterilising doses were stable for months when stored anhydrously, quenching rapidly with dissolution. Comparable nuclear polarisation to pyruvate at 6.7T was observed in a partially-ordered glycerol/alanine mix, potentially via a cross-effect mechanism. Impact: This has several novel impacts – it: (1) makes centralised manufacturing & storage possible with dual-purpose irradiation sterilising a sealed fluid-path; (2) demonstrates electron irradiation feasible for DNP; and (3) highlights how molecular environments could be partially controlled for polarisation optimisation.