Toward Hyperpolarized 19F Molecular Imaging via Reversible Exchange with Parahydrogen

Fluorine-19 has high NMR detection sensitivity-similar to that of protons-owing to its large gyromagnetic ratio and high natural abundance (100 %). Unlike protons, however, fluorine-19 (F-19) has a negligible occurrence in biological objects, as well as a more sensitive chemical shift. As a result, in vivo F-19 NMR spectroscopy and MR imaging offer advantages of negligible background signal and sensitive reporting of the local molecular environment. Here we report on NMR hyperpolarization of 19F nuclei using reversible exchange reactions with parahydrogen gas as the source of nuclear spin order. NMR signals of 3-fluoropyridine were enhanced by approximate to 100 fold, corresponding to 0.3% F-19 nuclear spin polarization (at 9.4 T), using about 50% parahydrogen. While future optimization efforts will likely significantly increase the hyperpolarization levels, we already demonstrate the utility of F-19 hyperpolarization for high-resolution hyperpolarized F-19 imaging and hyperpolarized F-19 pH sensing.