radiographic examination of arteries and veins, one of the procedures of diagnostic imaging. These structures cannot be differentiated from the surrounding organs in conventional radiography. It is therefore necessary to inject into the lumen of the vessels a substance that will distinguish them from the surrounding tissues. The contrast medium used is a water-soluble substance containing iodine. On the radiograph, iodine-containing structures cast a denser shadow than do other body tissues. The technique now in use was perfected in 1953.

A needle is used to puncture the main artery in the groin, armpit, or crook of the arm and to place a coiled wire in the artery. The needle is withdrawn, and a small, flexible hollow tube (catheter (catheterization)) is passed over the wire and into the artery. The wire is removed, and contrast medium is injected through the catheter. Both the arteries and the structures they supply with blood can be visualized. All organs of the body can be examined in this way. Radiographic evaluations of diseased arteries supplying the legs, the brain, and the heart are necessary before corrective surgical procedures are undertaken. See also angiocardiography.