Substance comparatively opaque to X-rays, which appears lighter on X-ray film and allows a body structure that does not normally contrast with its background to be seen clearly on the film. Common contrast media include barium sulfate and iodized organic compounds. They are given by the route that introduces them into the structure to be examinedswallowed or as an enema for the digestive tract, inhaled for the respiratory tract, or injected for blood vessels and for organs and tissues they supply. Serious reactions to contrast media are not infrequent. See also diagnostic imaging.
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