MRI uses a magnet and gives no ionizing radiation.  However, the MRI has a narrow tunnel that can produce claustrophobia and can’t be used in people with some kinds of metal in their body.  It is more expensive and if the subject moves during the scan, it must be done over. MRI shows soft tissue such as thickened ligaments better than CT and IV contrast can be given to show scar tissue in persons who have had previous spine surgery.