Autoradiography -- The making of a radiograph by introducing a radioactive tracer into a specimen and recording the radiation distribution on a photographic film or emulsion placed on or close to the specimen.

Cyclotron -- An apparatus for accelerating charged particles (e.g., protons, deuterons, or ions) to high energies by a combination of a constant magnet and an oscillating electric field. Such particle accelerators can be used to produce short-lived radioisotopes to use as labels/tags for experimental or medical diagnostic tracer materials.

Deoxyglucose (or 2-deoxyglucose) -- An analog of glucose with one less oxygen molecule, which can be taken up by cells as glucose is, but cannot be metabolized further than the first step in the glycolysis chemical pathway. The molecular formula is C₆H₁₂O₅.

Enzyme -- A protein molecule that catalyzes chemical reactions of other substances without itself being destroyed or altered upon the completion of the reactions. Made up of a complex of amino-acids, enzymes are part of every chemical reaction in living things. They aid in digestion, the growth and building of cells, and all reactions involving transformation of energy. Inside the cell, enzymes create RNA and DNA by facilitating the reaction of ribose with adenosine. They also specify the sites for linking to build RNA along a DNA template. Each enzyme works only on one specific substance (called the substrate). Enzymes are usually designated by the suffix -ase.

Enzyme kinetics -- The study of chemical reactions that are catalyzed by enzymes by measuring the reaction rates and investigating the effects of varying the conditions of the reactions.

Glucose -- A simple sugar found in many fruits and plants, and in the normal blood of all animals. It is the end product of carbohydrate metabolism and is the chief source of energy for living organisms. The molecular formula is C₆H₁₂O₆.

In vitro -- An experimental situation outside a living cell or organism; biological or chemical work done in the test tube, instead of all living systems. "In vitro" is Latin for "in glass."

In vivo -- An experimental situation in a living cell or organism; biological or chemical work done in living systems. "In vivo" is Latin for "in the living."

Isotope -- A chemical element having the same atomic number (i.e., number of protons in its nucleus) as another, but a different atomic mass (i.e., number of neutrons in its nucleus.) [See also "radioisotope."]

Metabolism -- The chemical reactions occurring in a living cell which provide energy for vital processes and activities, and assimilate new material. Energy metabolism (catabolism) breaks down food molecules to release chemical energy. Protein metabolism is the synthesis of protein and amino acids.

Phosphorylation -- The metabolic process of introducing a phosphate group into an organic molecule.

Positron emission tomography (PET) -- A functional imaging technique used to observe metabolic processes in the body. A PET scanner detects pairs of gamma rays emitted indirectly by a positron-emitting radioactive tracer, which is introduced into the body on a biologically active molecule. A computer then analyzes the scanning data and constructs three-dimensional images of tracer concentration within the body.

Radioisotope -- An isotope that is radioactive; i.e., that has an unstable nucleus and emits characteristic radiation during its decay to a stable form.

Radio-labeling or radio-tagging; radioactive tracer -- Replacing one element of a compound with one of its radioactive isotopes, so that the compound can be tracked through one or more reactions or systems by means of a radiation detector.

Thyroxine -- The major hormone secreted by the thyroid gland. Its chief function is to increase the rate of cell metabolism. It is also essential for central nervous system maturation and regulates a number of other functions.