Principle of MRI

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  • Created by: roopa
  • Created on: 31-03-15 08:09

How does an MRI machine work?

  • Protons inside of our body have spin and behave like tiny magnets.
  • The MRI machine provides a strong magnetic field which the protons precess abour.
  • Inside of the MRI machine are transmitting coils which provide pulses of radio waves at a frequency known as the Larmor frequency.
  • The protons absorb the energy from these radio waves and flip into a higher energy state.
  • When the magnetic field is removed, they flip back to their lower energy state, emitting photons of radio waves in the process.
  • The relaxation time of the protons depends on the surrounding tissue, the emitted waves are picked up by receiver coils.
  • Finally, a computer processes all the signals received and generates an image.

Note that the Larmor frequency varies for protons in different regions of the body so gradient coils alter the magnetic flux density going through the body,

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