Conversion of a proton pair para order into 13C polarization by rf irradiation, for use in MRI

We describe the theory of production of hyperpolarized C-13 in small organic molecules, for use as molecular contrast agents in MRI, by a two-step process. The first is a catalyzed hydrogenation with para-hydrogen in a small dc magnetic field under rf irradiation, resulting in a molecular proton pair in the pure para state. The second step converts this para order into net hyperpolarization of a nearby carbon 13 through a sequence of rf pulses at the resonance frequencies of both spin species. The final theoretical polarization is close to unity. The whole process, which was successfully implemented, takes a few seconds.