10.4.4

Magnetic Resonance Scanning

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Magnetic Resonance (MR) Scanner

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

Protons align

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.
Resonant frequency

Resonant frequency

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

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
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Measurements & Errors

2

Particles & Radiation

3

Waves

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Mechanics & Materials

5

Electricity

6

Further Mechanics & Thermal Physics (A2 only)

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Fields & Their Consequences (A2 only)

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Option: Turning Points in Physics (A2 only)

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    MR ScannerPut in order
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