When one thinks of the term nuclear medicine the first thing that comes to mind is radiation therapy for cancer. While this is one obvious use of radiation in medicine, it is far from the only application. Medical imaging would severely hindered without the ability of radioactive elements to decay and emit subatomic particles. I had the unfortunate experience of needing a bone scan recently and came face to face with the application of one of nature’s most rare element, Technetium.
Technetium is the lightest element that has no stable isotopes. Thus it is not generally found in nature. It was the first element to be artificially produced by bombarding molybdenum atoms with deuterons produced in a cyclotron by Perrier and SegrÃ¨ in 1937. The most stable isotope is Tc-98 with a half-life of about 4,200,000 years. It decays into ruthenium-98 by a process known as beta decay. For medicine, the metastable isotope Tc-99m, with a half life of 211,000 years is used. It is produced from the much shorter living element molybdenum-99 (half life 2.75 days) which is made from fission of highly enriched uranium. There are only five reactors in the world that produce Mo-99 and most of the Tc-99m used in medicine comes from those reactors.
Technetium-99 is used in imaging because it is a gamma-ray emitter. When very small doses are injected into a patient the Tc is absorbed into the bones over a period of a few hours. More Tc is absorbed in areas where active bone repair is taking place. Thus, when the gamma rays are detected by a special camera the areas of bone that have been damaged, and thus is under active repair, will light up brighter due to the increased concentration of the Tc. I had a bone scan of my feet done this week because of a suspected stress fracture due to my inclination to run. These type of fractures are incredibly difficult to ascertain by standard X-ray images. Fortunately for me the bone was not fractured and I am on my way back to marathon training.