Mallinckrodt plc has closed on a $690 million deal to sell its nuclear imaging business to St. Louis-based Iba Molecular Corp. The deal was first disclosed back in August of last year. The Staines-upon-Thames, U.K.-based company's imaging business produces the radioisotope molybdenum-99, from which technetium-99m is derived and is used in about 80 percent of all nuclear medicine procedures worldwide.