Sharif M et al. Serum hyaluronic acid level as a predictor of disease progression in osteoarthritis of the knee. Arthritis Rheum 38:760-767, 1995; Hochberg MC et al. Serum levels of insulin-like growth factor 1 in subjects with osteoarthritis of the knee. Arthritis Rheum 37:1177-1180, 1994
Stable isotopes of an element do not change over time. Atoms of unstable isotopes â also called radioisotopes--change into other elements over time through radioactive decay. Radioisotopes are used in many medical imaging and diagnostic procedures, with the isotope Tc-99m being used in 80 percent of tests.
1 Radioactivity tracers are commonly used in the medical field and also in the study of plants and animals. 2  Radiation is used and produced in nuclear reactors, which controls fission reactions to produce energy and new substances from the fission products.  Radiation is also used to sterilize medical instruments and food.