The goal of this study is to develop advances in cardiovascular diagnostic and treatment methods using magnetic resonance imaging (MRI), a test that uses a strong magnetic field and radio waves to show anatomic detail. For the scan, the patient lies on a table in a cylinder containing a magnetic field. He or she can communicate with a staff member at all times during the procedure.

Patients 18 years of age or older who require 1) catheterization of the leg arteries for diagnosis or treatment of blocked arteries, or 2) heart catheterization for diagnosis or treatment of coronary artery disease or other heart problems may be eligible for this study. Participants will undergo one of the following procedures:

Blood Flow Measurement Using Standard Techniques and MRI

For patients with blockage in a leg artery, blood flow will be measured before and after successful catheter-based treatment (angioplasty or stenting) using standard venous occlusion plethysmography and a newer MRI technique. (Patients whose treatment is not successful will not undergo follow-up blood flow measurements in this study.) For venous occlusion plethysmography, a large pressure cuff is placed around the upper or lower legs. Thin elastic bands called a strain gauge are placed around the calves to measure blood blow to the legs. The pressure cuffs are inflated for 5 minutes, preventing blood from flowing to the legs, and are then deflated, allowing the blood to rush to the legs. A smaller cuff is inflated to a low pressure, and the strain gauge measures this maximum blood flow to the legs for 1 or 2 more minutes. For the new MRI technique, blood flow is measured while the patient is in the MRI scanner. Flow is first measured with the patient at rest. Then, the large pressure cuff is inflated for 5 minutes. The cuff is deflated and additional images are taken. Before the cuff is deflated, a dye called gadolinium contrast is injected into an arm vein to brighten the images. Patients may undergo six to eight cuff inflations on four to six different days.

Fusion of X-Ray and MRI Images of Peripheral Arteries

For patients with blockage in a leg artery - Participants will undergo catheterization and MRI of the legs. Special plastic beads are taped to the leg(s) to help compare the MRI and x-ray pictures. For the catheterization procedure, x-rays of the blood vessels are taken to guide placement of the catheters. Contrast dye is injected to brighten the images of the blood vessels. These injections work well in normal and partly blocked arteries, but not in arteries that are completely blocked. For this study, patients first have an MRI scan of their legs. During the scan, gadolinium contrast dye is injected into an arm vein. Then, during the catheterization procedure, a computer aligns the MRI pictures with the x-ray pictures to see if the combined images allow the doctor to better see where to place the catheters.

Fusion of X-ray and MRI Images of the Heart

For patients undergoing heart catheterization will undergo MRI and heart catheterization. Special plastic beads are taped to the chest to help compare the MRI and x-ray pictures. Patients first have an MRI scan of their heart. During the scan, gadolinium contrast dye is injected into an arm vein. Then, during the catheterization procedure, a computer aligns the MRI pictures with the x-ray pictures to see if the combined images allow the doctor to learn more about the pattern of heart disease.

Heart rhythm, blood pressure, heart function, and breathing will be monitored during all the MRIs.