Intravascular Ultrasound is a diagnostic test that uses long, thin catheters and ultrasound to create images of the blood vessels of the body. The catheter is inserted and guided into specific vessels to diagnose vessel disease. The catheter has a small device called a transducer at the tip. The transducer both sends the sound waves and collects the “echos” that bounce back from the walls of the vessel. A computer uses this information to form the images of the vessel. These images can help diagnose stenosis (narrowing) and vessel disease (such as atherosclerosis).