Magnetic Resonance Imaging of Narrowed Arteries

This study will compare four methods of imaging arteries: * angiography (x-ray picture) * intravascular ultrasound (ultrasound from inside the artery) * magnetic resonance imaging (MRI) from outside the body * MRI using an antenna to take pictures inside the arteries of the pelvis Standard angiography shows blockages inside the artery, but does not provide any information about the arterial wall itself. New ways of looking at the artery walls with MRI and ultrasound may provide insight into how arteries cause disease. Patients 21 years of age and older who require catheterization and angiography of the heart, kidney, or leg arteries because of atherosclerosis (narrowing of the arteries), may be eligible for this study. Participants will undergo MRI and intravascular ultrasound of the arteries immediately after their catheterization and angiography. The additional imaging will add from 1 to 2 hours to the angiogram procedure. * Angiography: Using the sheaths already in place in the groin artery, catheters (flexible plastic tubes) are placed inside the arteries in order to inject a contrast dye to take x-ray pictures. (Patients who had an angiogram of the leg artery as part of their medical care will not repeat this test.) * Intravascular ultrasound: An anti-clotting drug called heparin is given through a vein to prevent clot formation. Blood samples are taken during the test to see if more heparin is needed. Special wires are used to guide the catheters to the proper location inside the arteries. A special ultrasound catheter is advanced over one of these wires to the large artery that supplies blood to the legs. X-rays are used to help the physician place the ultrasound in the correct location to take ultrasound pictures of the artery wall. * Magnetic resonance imaging: A special MRI catheter is advanced through the catheter in the groin. With the catheter in place, the patient is carried to a stretcher and moved into a long metal cylinder (the MRI scanner) for