PhysicsChapter 11: Medical Imaging
Doppler Ultrasound and Blood Flow
Doppler ultrasound
Definition
Doppler ultrasound uses the Doppler effect to measure motion, particularly the movement of blood.
Formula / Key Relation
When ultrasound reflects from moving blood cells, the reflected frequency can differ from the transmitted frequency. This difference is called the Doppler shift. The shift depends on: transmitted frequency; blood speed; speed of sound in tissue; angle between beam and blood flow. A common relation is: Δf = 2f₀v cosθ / c where: `Δf` = Doppler frequency shift `f₀` = transmitted frequency `v` = blood speed `θ` = beam-flow angle `c` = sound speed The factor `2` occurs because the Doppler interaction effectively involves the incident and reflected wave paths. **Δf = 2f₀v cosθ/c**
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Review the key facts, formulas and checks before you move on.Doppler Ultrasound and Blood Flow
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DOPPLER
- Moving blood → frequency shift
- `Δf ∝ v cosθ`
60-second revision
- Frequency shift gives information about blood velocity.
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