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 Naturally occurring and man-made radionuclides, also called radioactive isotopes or radioisotopes, are unstable, and emit radiation as they spontaneously disintegrate, or decay, to a stable state. 2  The radionuclide used almost always for the irradiation of food by gamma rays is cobalt-60.he Food irradiation process. The radiation used in processing materials is limited to radiation from high-energy gamma rays, X-rays and accelerated electrons.