Magnetic Resonance Scanning
Physics: AQA A Level, topic 10.4.4
Magnetic Resonance (MR) Scanner
MR scanners use the magnetic properties of protons to form an image.
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
- 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
- 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.
Test yourself on Magnetic Resonance Scanning
MR Scanner
What is the typical strength of the magnetic field used in an MR scanner?
What do spinning protons absorb and re-emit when a patient is in an MR scanner?