| a radiopaque substance injected into a part of the body, as the stomach or duodenum, to provide a contrasting background for the tissues in an x-ray or fluoroscopic examination. |
contrast medium n.
A substance, such as barium or air, used in radiography to increase the contrast of an image. A positive contrast medium absorbs x-rays more strongly than the tissue or structure being examined; a negative contrast medium, less strongly.