Process for preparation of MR contrast agents

The present invention provides a process for the preparation of an MR contrast agent, said process comprising: i) obtaining a solution in a solvent of a hydrogenatable, unsaturated substrate compound and a catalyst for the hydrogenation of said substrate compound; ii) introducing said solution in droplet form into a chamber containing hydrogen gas (H 2 ) enriched in para-hydrogen (p- 1 H 2 ) and/or ortho-deuterium (o- 2 H 2 ) whereby to hydrogenate said substrate to form a hydrogenated imaging agent; iii) optionally subjecting said hydrogenated imaging agent to a magnetic field having a field strength below earth's ambient field strength; iv) optionally dissolving said imaging agent in an aqueous medium; v) optionally separating said catalyst from the solution of said imaging agent in said aqueous medium; vi) optionally separating said solvent from the solution of said imaging agent in said aqueous medium; and vii) optionally freezing the solution of said imaging agent in said aqueous medium.