Magnetic Resonance Scanning

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Magnetic Resonance (MR) Scanner

MR scanners use the magnetic properties of protons to form an image.

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Protons align

  • Hydrogen atoms in the body contain spinning protons, predominantly in water.
  • Protons align with and against the applied field.
  • A slight excess number of protons align with the applied magnetic field.
    • This magnetic field is very large, with typical strengths of 1 or 2 Tesla.
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Resonant frequency

  • The excess is proportional to the applied field.
  • Spinning protons wobble (or precess) with a resonant frequency proportional to the applied field.
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Radio frequency pulse

  • An RF (radio frequency) pulse is applied and then switched off.
  • Protons which absorbed the RF energy now retransmit it, producing the NMR (nuclear magnetic resonance) signal.
  • Differences in the tissues alter the retransmitted signal, which is processed by a computer.

Jump to other topics

1Measurements & Errors

2Particles & Radiation


4Mechanics & Materials


6Further Mechanics & Thermal Physics (A2 only)

7Fields & Their Consequences (A2 only)

8Nuclear Physics (A2 only)

9Option: Astrophysics (A2 only)

10Option: Medical Physics (A2 only)

11Option: Engineering Physics (A2 only)

12Option: Turning Points in Physics (A2 only)

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