Ultrasound and Other Images of Artery Blockages

Background: \- Treatments for partly blocked carotid arteries are determined by a person s symptoms and by tests that show how severe the blockage is. Studies show that the material that blocks an artery is more important in spotting future problems than how tight the blockage is. Researchers want to develop better imaging studies to find which blockages are more high-risk. Objectives: \- To use imaging studies to look at high-risk carotid artery blockages. Eligibility: \- Individuals at least 21 years of age whose ultrasound exams show a major carotid artery blockage. Design: * Participants will be screened with a medical history, physical exam, blood and urine tests, , an ultrasound scan and a magnetic resonance imaging (MRI) scan. * Participants will have ultrasound and other scans to obtain pictures of the arteries. The scans will use drugs that may help study doctors get a better picture of the blood vessels and blockages. * Participants will have followup phone calls yearly for 3 years. If a participant later has surgery to remove the blockage, the surgeon will save part of it for future study.