Angiography is a diagnostic procedure that allows direct visualization of blood vessels in the body. It is generally performed to detect abnormalities of the blood vessels, or to evaluate the blood supply to various organs in the body. Angiography is performed by the injecting radiographic contrast material (dye) into the blood vessels via a catheter that is placed directly into the artery or vein. The catheter, which is a very thin flexible tube, is passed into the vessel through a needle puncture site in the vessel. Angiograms are very important in diagnosing and treating a wide variety of medical problems.