MRI is similar to a CT scan, although it uses powerful magnets to take hundreds of cross-sectional pictures. A computer then puts the pictures together to form whole images of internal organs. MRIs are used to detect abnormalities in the colon and other parts of the body.
In a traditional MRI, the patient is placed on a bed that slides inside a tube, where the test is conducted. An open MRI, does not require that the patient be placed in a tube, but is done in the "open." This is an option for patients who are claustrophobic or too large for traditional MRI.