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How fMRI Works

        Science | Devices

fMRI Imaging: How Is an fMRI Done?
fMRI Imaging: How Is an fMRI Done?

An fMRI scan is usually performed on an outpatient basis. This means you will come into the hospital for the scan and leave afterward. During the test you may wear a hospital gown or your own clothes, but you can't bring anything metal (zippers, clips, pins, glasses) into the room, because it could interfere with the MRI machine.

During the test, you lie on a table. Your head may be placed in a brace to hold it still. Then you are slid headfirst into the large, cylindrical MRI machine. You may be given earplugs to mask the sound -- MRI machines tend to be very noisy.

While the machine is scanning your brain, you will be asked to perform a task that increases oxygenated blood flow to a particular part of your brain. For example, you may tap your thumb against your fingers, look at pictures or answer questions on a computer screen. The test can last anywhere from a few minutes to an hour or more. After the scan is done, a specialist called a radiologist will interpret the results.

Although an fMRI test doesn't use radiation, its strong magnetic field and radio waves may not be recommended for certain groups of people including:

  • Pregnant women
  • People with an internal defibrillator or pacemaker
  • Those with artificial heart valves or limbs
  • People with cochlear implants
  • People with an infusion catheter
  • Those with clips used on brain aneurysms
  • Women with an intrauterine device (IUD)
  • People with metal pins, screws, plates or surgical staples.