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.
Radionuclides used in PET scanning are isotopes with short halfâlives, such as carbon-11 (~20 min), nitrogen-13 (~10 min), oxygen-15 (~2 min) and fluorine-18 (~110 min). These radionuclides are added into compounds normally used by the body such as glucose (or variations of glucose), water or ammonia.Such labelled compounds are known as radiotracers. In some situations, the patient is required to breath oxygen gas labelled with oxygen-15.adioactive isotopes and radioactively labelled molecules are used as tracers to identify abnormal bodily processes. This is possible because some elements tend to concentrate (in compound form) in certain parts of the body â iodine in the thyroid, phosphorus in the bones and potassium in the muscles.