tracer

1. An element or compound containing atoms that can be distinguished from their normal counterparts by physical means ( e.g., radioactivity assay or mass spectrography) and can thus be used to follow (trace) the metabolism of the normal substances. 2. A colored or radioactive substance that can be injected in the region of a tumor (melanoma, breast, etc.) to map the flow of lymph from the tumor to its nearest nodal basin; used in sentinel node detection. 3. A colored substance ( e.g., a dye) used as a t. to follow the flow of water. 4. An instrument used in dissecting out nerves and blood vessel s. 5. A mechanical device with a marking point attached to one jaw and a graph plate or tracing plate attached to the other jaw; used to record the direction and extent of movements of the mandible. SEE ALSO: tracing (2). [M.E. track, fr. O. Fr. tracier, to make one's way, fr. L. traho, pp. tractum, to draw, + -er, agent suffix]

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trac·er 'trā-sər n a substance used to trace the course of a process specif a labeled element or atom that can be traced throughout chemical or biological processes by its radioactivity or its unusual isotopic mass

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n.

a substance that is introduced into the body and whose progress can subsequently be followed so that information is gained about metabolic processes. Radioactive tracers, which are substances labelled with radionuclide, give off radiation that can be detected on a scintigram or with a gamma camera. They are used for a variety of purposes in nuclear medicine. See MUGA scan, positron emission tomography, SPECT scanning.

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trac·er (trāsґər) 1. a means or agent by which certain substances or structures can be identified or followed, as a radioactive tracer. 2. a mechanical device by which the outline of an object or the direction and extent of movement of a part may be graphically recorded; see also tracing. 3. a dissecting instrument for isolating vessels and nerves.