Why an MRI?

Friday, 16 March 2012 From Issue Vol. XX No. 11 By  Dr. Iain Corness

MRI (magnetic resonance imaging) is one of the battery of radiological diagnostic examinations that can be done.  The procedure is similar to an X-Ray, in the fact that the end result shows the internal structures of the body with a test that produces very clear pictures - but without the use of X-rays.  MRI uses a large magnet, radio waves, and a computer to produce these images.

Some folk are a little apprehensive about these expensive tests, but the risks to the average person are negligible.  The MRI uses magnetic fields, rather than radio-active imaging.  However, the magnetic field is very strong.  Walk into the examination room and the MRI can wipe the details from the magnetic strip encoding on your credit card, stop your watch and even pull the stethoscope from the doctor’s pocket!

MRI is also different from X-Rays in what it can pick up.  The MRI can detect tumors, infection, and other types of tissue disease or damage.  It can also help diagnose conditions that affect blood flow.  Tissues and organs that contain water provide the most detailed MRI pictures, while bones and other hard materials in the body do not show up well on MRI pictures, as opposed to X-Rays which do show bone well but not soft tissue.  For these reasons, MRI is most useful for detecting conditions that increase the amount of fluid in a tissue, such as an infection, tumors, and internal bleeding.  In some cases a contrast material may be used during the MRI scan to enhance the images of certain structures.  The contrast material may help evaluate blood flow, detect some types of tumors, and locate areas of inflammation.

People who have had heart surgery and people with the following medical devices can be safely examined with MRI: surgical clips or sutures, artificial joints, staples, cardiac valve replacements (except the Starr-Edwards metallic ball/cage), disconnected medication pumps, vena cava filters or brain shunt tubes for hydrocephalus.

However, some conditions may make an MRI examination inadvisable.  Tell your doctor if you have any of the following conditions: heart pacemaker, cerebral aneurysm clip (metal clip on a blood vessel in the brain), pregnancy during the first three months (we are just being super cautious here), implanted insulin pump (for treatment of diabetes), narcotics pump (for pain medication), or implanted nerve stimulators (“TENS”) for back pain, metal in the eye or eye socket, cochlear (ear) implant for hearing impairment, or implanted spine stabilization rods.

I think most people are familiar with the standard X-Ray procedure, stand there, breathe in, hold it, now breathe out routine, but MRIs are a little different.  These are done with you lying there and inserted into the MRI scanner, which is like a tunnel.  Those people who are claustrophobic can have a little problem here, as the MRI “tunnel” is very tight.  When I had my own MRI done I noticed that my nose was close to the top of the tunnel and both elbows were brushing the sides, and I am considered a reasonably slim individual.  I have to say that although not claustrophobic, I do not particularly like being in enclosed spaces, and found that the best way to endure the MRI was to pretend I was lying relaxing in a field.

During the procedure, which can take up to an hour, you can hear the operator talking to you, and he or she can hear your reply, but you still will feel rather isolated in your magnetic tunnel.  You can also hear (and feel) muffled thumps and groans that come from the tube, which can be somewhat unsettling.

In some cases a contrast material may be used during the MRI scan to enhance the images of certain structures which may help evaluate blood flow, detect some types of tumors, and locate areas of inflammation.  The contrast material is injected via a vein, and the MRI operator will advise you when this is being injected.  You may feel a warmth or even tingling feeling as this is happening, but this is not worrisome.

The radiologist then reviews the pictures produced and will advise you of the outcome.  I hope it will be good news!

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