Medical providers are scrambling to find medical uranium after an unplanned shutdown of a Canadian nuclear reactor in May sparked a global uranium shortage, making clear the need for a domestic supply of medical isotopes. The shortage has forced some doctors to delay patient care or shift to more costly medical tests.

Most of the world’s enriched uranium is stockpiled for weapons — the primary use for the energy source. But some enriched uranium makes it's way into medical use.

"We do not use highly enriched uranium for any medical use — not directly," Dr. James O'Donnell, division chief of nuclear medicine at University Hospitals Case Medical Center in Cleveland, Ohio told FOXNews.com. "But it’s a precursor — a building block — that can be put into a nuclear reactor, which causes fission and breaks it apart. One of the byproducts we are left with is technetium, a medical isotope used to perform imaging tests."

Technetium is like a light bulb, O'Donnell explained.

"We screw it on to a molecule of medicine that goes to a certain organ," he said. "We are actually experiencing a shortage of technetium now. We rely on five reactors around the world, which are located in Canada, South Africa and three in Europe." Canada's reactor shutdown in May.

Technetium — a rapidly decaying substance — has a shelf life of just 67 hours, making it impossible to stockpile. Technetium-99m, a radioactive byproduct of Mo-99, is used in over 14 million nuclear medicine procedures in the United States each year.

"It’s one of our favorite 'light bulbs' for bone scans, cardiac scans, lung scans, liver scans, etc," O'Donnell said, noting that technetium is "virtually harmless."

"It’s used in microgram quantities for its properties of radioactivity. We want to detect externally where it goes in the body — what organ it goes to. It [technetium] gives off gamma rays, which are detected from a gamma camera."

The American Medical Isotopes Production Act of 2009, a bill sponsored by Rep. Edward Markey, D-Mass., who chairs the subcommittee, and Rep.Fred Upton, R-Mich., would provide the Secretary of Energy with $163 million to promote the production of molybdenum-99 in the United States.

It would also require that medical isotopes produced in the United States be made from low-enriched uranium, and any imported isotopes be made that way as well.

Medical imaging procedures that rely on medical isotopes improve patient care and can reduce costs.

FOXNews.com's Karlie Pouliot and Reuters contributed to this report.