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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.
(Medicine) med a radiopaque substance, such as barium sulphate, used to increase the contrast of an image in radiography
a radiopaque substance introduced into a part of the body to provide a contrasting background for the tissues in an x-ray examination.