How does magnetic resonance imaging (MRI) work?

Magnetic resonance imaging (MRI) scans take pictures of the unseen and make them visible. How? An MRI takes advantage of the fact that we are mostly made up of water (H2O—two parts hydrogen to one part oxygen). Using a powerful magnetic field, the machine polarizes the protons in hydrogen molecules so they stand up and point in one direction, then sit back down. Imagine "the wave" rippling through the stadium seats at a baseball game. That's what happens to H2 molecules when an MRI machine is turned on.

The incessant pinging noise, which can be so bothersome to someone inside the MRI tube, signals another dose of energy that starts another "wave" all over again. As the machine pings away, radio waves (not x-rays) organize the ups and downs and they're assembled into a picture of your insides.

The process of magnetic resonance imaging (MRI) can be explained as:

  1. Nuclei of the molecules within a human body are randomly aligned magnetically.
  2. When we walk into a room with a strong magnetic field, those same molecules align themselves to the magnetic field.
  3. For an MRI examination, a coil placed on or around you generates a pulse of energy.
  4. The molecules then realign with the pulse of energy.
  5. When the pulse is turned off or reapplied, the molecules return to their positions, creating a detectable signal.
  6. These detectable signals are processed by the computer into a series of images.
  7. Patients feel no pain during the MRI examination.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.