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.
Radiation is used in nuclear medicine and radiology. In nuclear medicine, radioactive materials known as radioisotopes, or radiopharmaceuticals, are introduced into the body. In radiology, X-rays enter the body from outside. According to the Center for Nuclear Science and Technology Information, about one-third of all procedures used in modern hospitals involve radiation or radioactivity.