Shared Medical Services What is MRI?

What is a MRI? | FAQs and links

How does an MRI scan differ from a CT scan?

An MRI scan is capable of taking pictures from almost every angle, while a CT scan can only show pictures horizontally.  Generally, MRI's are also more detailed than a CT.  Since MRI scans use magnetic and radio waves instead of radiation, it is also less risky in most situations than a CT scan. 

How does an MRI scan work?

The patient lies inside of a large, cylinder-shaped magnet, and radio waves are sent through the body.  These waves affect the body's atoms and force the nuclei into a different position.  As the nuclei move back into position, they send out their own radio waves.  The MRI scanner picks up these signals and then a computer turns them into pictures based on the location and strength of the incoming signals. 

What can an MRI diagnose?

  • Heart disease
  • Heart attack
  • Acute stroke, and vascular disease which can lead to stroke
  • Sports injuries
  • Many forms of cancer
  • Brain Aneurysms
  • Tumors
  • Spine injuries
  • Abdominal defects or disease
  • Joint, tissue, or bone problems

Can anyone have an MRI scan?

People who have implanted metal devices, or other metal in their body, may not receive an MRI scan due to the magnetic field and radio waves involved.  Anyone who has the following will not be able to have an MRI:

  • Heart pacemaker
  • Cochlear implant (an internal hearing aid)
  • Metal heart implants
  • Metal surgical implants (metal rods, clips, plates, or pins)
  • Surgical implants to stop bleeding in the brain
  • Metal shrapnel
  • Any other metal that is susceptible to the MRI's magnetic field

What are the risks associated with an MRI scan?

There are not many known risks or dangers with an MRI scan.  It is a painless procedure, and there is no radiation exposure.  An undetected metal implant could cause some issues due to the MRI's magnetic field.  A woman in her first 12 weeks of pregnancy may not have an MRI scan done because of a slight risk to the fetus.  Also, because patients lie in an enclosed area , some people become claustrophobic during the scan.


Radiology Info
American Cancer Society
National Cancer Institute
eMedicine Health


Wondering what your doctor will be reviewing? Click below on a thumbnail to view an actual MRI scan.