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a chemical element, atomic number 81, atomic weight 204.37, symbol Tl. (See Appendix 6.) Its salts are active poisons that may cause alopecia, liver and kidney damage, blindness, and neurologic and psychic symptoms such as ataxia, restlessness, delirium, hallucinations, delusions, and semicoma.
thallium 201 a radioactive isotope of thallium having a half-life of 3.05 days and decaying by electron capture with emission of gamma rays. It is used as a diagnostic aid in the form of thallous chloride Tl 201.
thallium scan a scintiscan involving the use of thallium 201. The radioisotope is administered intravenously and localizes, like calcium, in the myocardium. A scintillation camera produces an image of the distribution of the radioisotope. Areas of inadequate perfusion appear as “cold spots,” thus pinpointing the site of occlusions of the coronary arteries.

The thallium scan offers many advantages. It is noninvasive except for the administration of the radioisotope, which involves a radiation dose slightly larger than that received during a chest x-ray, and is extremely accurate.

The thallium-201 may be administered while the patient is exercising on a treadmill and being monitored by electrocardiogram. Subsequent scintigrams show areas of inadequate perfusion. This test is less likely than conventional exercise or stress testing to indicate disease when none is present and is more likely to detect disease when it is present. See also exercise thallium scintigraphy and myocardial perfusion scintigraphy.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


Symbol for thallium.
Farlex Partner Medical Dictionary © Farlex 2012


Symbol for thallium
Medical Dictionary for the Health Professions and Nursing © Farlex 2012