Study candidates will be screened with a medical history and physical examination. Participants will have a MRI scan and blood drawn at Suburban Hospital before the angioplasty and again either 1 to 3 days or 2 weeks after the procedure. Before the MRI scan is begun, a catheter (a thin plastic tube) is inserted in an arm vein and 90 milliliters (about 3 ounces) of blood is drawn. The patient then lies on a table that slides into the MRI scanner-a large donut-shaped machine with a magnetic field. A flexible, padded sensor called an MRI coil is placed over the area to be imaged; this device is used to improve the quality of the pictures. During the scan a contrast material called gadolinium is injected through the catheter. Gadolinium brightens the image of the blood vessels. The procedure lasts up to 2 hours.