Validation of MRI Measurement of Cardiac Blood Flow

This study will test the accuracy of magnetic resonance imaging (MRI) in measuring cardiac perfusion (blood flow). MRI of the heart can measure blood flow to heart muscle, but collateral coronary arteries (vessels that supply blood to the heart muscle) may reduce the accuracy of the measurements. This study will perform special measurements of coronary artery flow and pressure in patients undergoing heart catheterization and catheter-based treatment (angioplasty and stenting) in order to compare for accuracy with cardiac MRI. Patients 21 years of age and older with coronary artery blockage may be eligible for this study. All participants undergo cardiac MRI, to produce images of the heart, as well as special invasive blood flow testing during heart catheterization, angioplasty, and stenting. During MRI, the subject lies on a table that can slide in and out of the scanner (a narrow cylinder), wearing earplugs to muffle loud knocking and thumping sounds that occur during the scanning process. The procedure lasts about 45 to 90 minutes. Since the heart moves during breathing, subjects are asked to hold their breath intermittently for about 5-20 seconds. A medicine called dipyridamole is injected through a vein in the subject's arm to increase blood flow to the coronary arteries and help detect blockages. Pictures are taken of the heart before, during, and after the dipyridamole injection. Another medicine called gadolinium is also given through a vein. This medicine brightens the images to measure blood flow. During a separate catheterization, angioplasty, and stenting procedure, subjects undergo additional invasive tests. The additional tests use a special guidewire to measure coronary artery pressure and blood flow, as well as a special ultrasound to look inside the artery. Patients have a repeat MRI about 2 months after the catheterization.