Contrast

Short for "contrast media." Contrast media are X-ray dyes used to provide contrast, for example, between blood vessels and other tissue.

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1. A comparison in which differences are demonstrated or enhanced. 2. In radiology, the difference between the image densities of two areas is the c. between them; this is a function of the number of x-ray photons transmitted or the strength of the signals emitted by the two regions and the response of the recording medium. [L. contra, against, + sto, pp. status, to stand]

- simultaneous c. the enhancement of the visual sensation of white when a white object is viewed adjacent to a black object; the black object also appears blacker as a result of the contiguity of white. Adjacent complementary colors also appear brighter; e.g., green appears a brighter green and red a brighter red if these two colors are viewed side by side.

- successive c. the visual effect caused by viewing a brightly colored object and then a gray surface; the latter appears tinged with the complementary color of the object. Viewing a surface colored in the complementary color of the object rather than in gray enhances the color intensity of the surface.

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n.

1. short for contrast medium, e.g. post-contrast CT scan.

2. the difference in the shade of grey between different tissues on a diagnostic image, such as radiograph or CT scan (see grey scale).

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con·trast (konґtrast) [contra- + L. stare to stand] 1. the degree to which light and dark areas of an image differ in brightness or in optical density. 2. in radiology, the difference in optical density in a radiograph that results from a difference in radiolucency or penetrability of the subject. Called also radiocontrast.