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How Does an MRI Work?

Posted by Johnson Memorial Health on Jan 6, 2015 10:00:00 AM

Magnetic resonance imaging (MRI) is the best way for doctors to see inside your body without doing so invasively. It uses a magnetic field and radio waves to create detailed images of your organs, tissues, and skeletal system.

MRI machines are usually large, so they might be intimidating, especially if you've never had one of these tests before. But we want to help put your anxiety to rest because you have nothing to fear. If you have been scheduled for an MRI exam, you might be curious as to what you can expect and how it works. 


What to expect

As you prepare for your MRI, you will be asked to change into a gown and remove any jewelry, glasses, watches, hearing aids, underwire bras (essentially anything with metal that might skew your results).

The MRI machine looks like a tube that has both ends open. You lie down on a moveable table that slides into the opening, and you will be asked to hold very still because you don't want to blur the resulting images. There are no moving parts around you, and the procedure is painless.

During the MRI scan, the internal part of the magnet produces repetitive tapping, thumping and other noises. (Earplugs or music may be provided to help block the noise.) If you are worried about feeling claustrophobic inside the MRI machine, talk to your doctor beforehand. You may receive a sedative before the scan.

How it works

The MRI machine creates a strong magnetic field around you. When this happens, the atoms in your body (which normally spin in random directions like tops) line up in north and south directions, half going each way. A few atoms are unmatched in either direction.

When radio waves are applied, the unmatched atoms spin the other way. When the radio frequency is turned off, the extra atoms return to their normal position which emits energy. This energy sends a signal to the computer which then uses a mathematical formula to convert the signal into an image.

In some cases, a contrast material, typically gadolinium, may be injected through an intravenous (IV) line into a vein in your hand or arm. The contrast material enhances the appearance of certain details.

Why it's done

MRIs produce high-quality images that help diagnose a variety of problems. You might have an MRI of your:

  • Brain and spinal cord to diagnose tumors, stroke, spinal cord injuries, MS, aneurysms
  • Heart and blood vessels to assess the size and function of the heart chambers, damage caused by a heart attack or heart disease, inflammation or blockages in blood vessels
  • Bones and joints to evaluate arthritis, bone infections, tumors of the bones and soft tissues, disk abnormalities
  • Breasts to detect breast cancer in women who have dense breast tissue or are considered high risk
  • Internal organs to check for tumors or abnormalities in the liver, kidneys, spleen, pancreas, overies, prostate

After your MRI is finished, a radiologist will analyze the images from your scan and report the findings to your doctor, who will then follow up with you. 

Overall, MRIs are painless and helpful in diagnosing medical conditions. If you have one in your future, you can rest easy knowing that you are in good hands with Johnson Memorial Health.


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Topics: MRI