Nuclear medicine requires the use of medical radioisotopes for a wide variety of procedures, which have saved millions of lives. The most commonly used medical radioisotope is technetium 99 m, which is usually derived from the molybdenum created in medical research reactors fueled with above-average levels of enriched uranium. But the number of these reactors has declined to a handful of widely scattered facilities, at the same time as there is increasing concern over the risks of shipping large amounts of highly enriched uranium fuel—often enriched as high as 90 percent, a level considered "weapons grade"—over long distances. One solution tried in the past was to convert research reactors to use lower levels of enriched uranium. An alternative may be to use particle accelerators in place of reactors for producing molybdenum. Another possibility would be for medical practitioners to switch to some other, yet-to-be-determined, non-fission-produced isotopes. In either case, much more research will be needed, along with funding and support from the public and private sectors.