Absorbing and blocking radiant energy, e.g. X-rays.
Having the property of absorbing, and therefore being opaque to, X-rays. Radio-opaque materials, many of them containing iodine, are used as contrast media in radiography. Barium salts are also radio-opaque and used in barium ‘meals’ and enemas for the investigation of the digestive tract by X-rays.
Substances which absorb x-rays, rather than transmitting them, appear white on X-ray film and are described as radio-opaque. This is true of bones, teeth, certain types of gall-stones, renal stones and contrast media (such as barium) used to enhance the accuracy of radiographic imaging.