For MRI, the subject lies flat on a table that can slide in and out of the scanner, a metal cyclinder. Special antennas, covered in pads, are placed against the subject s body. The scan time can vary from 20 minutes to 2 hours, with most scans lasting between 45 and 90 minutes. The subject may be asked to wear adhesive patches on the chest for monitoring the heart and a belt or finger pad for monitoring breathing. During the test, a contrast agent called gadolinium may be injected. This substance brightens the heart and arteries during the scan, providing a better picture of blood flow.