According to WebMD, an open MRI is a magnetic resonance imaging machine that has a larger opening than a standard MRI machine. Some open MRI machines do not completely surround the body, but such machines cannot perform certain MRI scans.
In any MRI machine, a patient lays on a table that slides into the area that contains the magnet, which uses radio waves and pulses to take pictures of organs and structures inside the body. WebMD states that an open MRI machine is typically used for patients who are claustrophobic or overweight. However, not all medical centers can provide this type of MRI.