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Radioactive Tracers

Specific Applications

Radioactive tracers are widely used to diagnose heart problems. Narrowing of the coronary arteries leads to coronary artery disease which often manifests itself as angina. Radiopharmaceuticals allow visualization of the blood supply to the heart tissue. ⁹⁹mTc-labels are used (e.g., sestamibi), but thallium-201 (²⁰¹Tl) has advantages. After reaching the heart tissue, it moves from the blood into the heart cells. Healthy cells then eliminate about 30% of the peak level of ²⁰¹Tl in about two hours. Damaged cells (e.g., from ischemia) will move the ²⁰¹Tl more slowly. Thus,²⁰¹Tl gives information on both the health of the heart tissue itself and the blood flow to it.

An exciting new area of use combines radioactive tracers with monoclonal antibodies (MoAbs). Antibodies are proteins that interact with a foreign substance (antigen) in a specific way. Advances in genetic technology allow biochemists to make MoAbs for many specific substances. Characteristic compounds on the surfaces of cancer cells can act as antigens. When radionuclide-labelled MoAbs are injected into the body, they attach to cancer cells with the corresponding antigen. The cancer cells can then be imaged, revealing their location and size. Three-dimensional imaging gives much guidance for subsequent surgery. Radionuclides can also be attached which emit cell-destroying radiation and thus kill cancer cells predominantly. Radiolabelled MoAbs promise to have more applications in the near future.

Resources

Books

Bernier, Donald R., Paul E. Christian, and James K. Langan, Editors. Nuclear Medicine: Technology and Techniques. 3rd Edition. St. Louis: Mosby, 1994.

Carlisle, Rodney P. Encyclopedia of the Atomic Age. New York: Facts on File, 2001.

Periodicals

Davis, Lawrence Paul, and Darlene Fink-Bennett. "Nuclear Medicine in the Acutely Ill Patient-I." Critical Care Clinics 10 (April 1994): 365-381.

Reba, Richard C. "Nuclear Medicine." Journal of the American Medical Association 270 (July 1993): 230-232.

Zaret, Barry L. and Frans J. Wackers. "Nuclear Cardiology." New England Journal of Medicine 329 (September 1993): 775-783.

Other

American College of Nuclear Physicians. Nuclear Medicine T.V. Series. Chicago: Orbis Broadcasting Group, 1995. 7 Videocasettes.

Dónal P. O'Mathúna

KEY TERMS

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Anger scintillation camera: —A device used to detect gamma rays from radioactive tracers. It converts the energy from the radiation into light and then electrical signals which are eventually recorded on a photographic plate.
Isotopes: —Two molecules in which the number of atoms and the types of atoms are identical, but their arrangement in space is different, resulting in different chemical and physical properties.
Monoclonal antibody: —A protein which interacts with a foreign substance (antigen) in a specific way. They are monoclonal when they are produced by a group of genetically identical cells.
Radioactive tracer: —A substance that is labeled with a radioactive isotope to allow easier detection and measurement.
Radionuclide: —Radioactive or unstable nuclide.
Radiopharmaceuticals: —Radioactive tracers with medical applications that are administered like other drugs.
Scintigraphy: —The process of obtaining images of radioactive tracers using scintillation detectors.
Scintillation: —A burst of light given off by special materials when bombarded by radiation.
Single photon emission computed tomography (SPECT): —The process by which gamma radiation from radionuclides which emit a single photon per decay is converted into three-dimensional images. It is a computer-based data processing method.
Tomography: —A method of data processing by computers which converts numerous planar images of an object into three-dimensional images or slices through the object. It is used in many different scanning procedures.
Tracer principle: —The general principle discovered by George de Hevesy in 1912 that isotopes of the same element have the same chemical properties. They act in the same way in chemical and biological reactions.

Additional topics

Science EncyclopediaScience & Philosophy: Quantum electronics to ReasoningRadioactive Tracers - Tracer Principle, Tissue Specificity, Preparation And Administration Of Radioactive Tracers, Detection And Imaging, Anger Scintillation Camera