False-colour arteriograph (angiograph) of a normal right lung, showing the branching tree" of arteries arising from a division in the main pulmonary artery that pumps blood from the heart to both lungs. Angiography is the x-ray examination of arteries that have been outlined by prior injection of a radio-opaque contrast medium. This has the effect of making the arteries appear almost as well-defined as bone appears on a normal X-ray film. Angiography is used to check for the presence of atherosclerosis, the formation of fatty, atheroma plaques on the arterial walls that leads to a restriction in the supply of blood to the lung."