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