Doppler Effect & Doppler Instrumentation

Doppler Effect

Change in frequency of a wave in relation to an observer moving relative to the wave source.

Doppler shift

Helps detect blood flow direction, velocity, and turbulence.

Christian Doppler

He first described how the observed frequency of waves (sound, light, etc.) changes due to the relative motion between the source of the waves and the observer

1842

In what year did Christian Doppler discovered Doppler Effect?

Positive Doppler Shift

Flow towards the transducer

Negative Doppler Shift

Flow away from the transducer

f' = f(v + vo) / (v - vs)

Doppler shift formula

• Continuous Wave (CW) Doppler

• Pulsed Wave (PW) Doppler

• Color Doppler

• Power Doppler

Types of Doppler Ultrasound

Continuous Wave (CW) Doppler

• Use two crystals: one sends, one receives.

• Measure high-velocity flows accurately (e.g., cardiac valves)

• No range resolution—can’t pinpoint exact depth.

Pulsed Wave (PW) Doppler

• Uses one crystal that sends and receives alternately.

• Allows depth-specific sampling (range resolution).

• Subject to aliasing when velocity is too high.

Color Doppler

• Overlays flow information in color on B-mode image.

• Red = toward, Blue = away (remember: BART).

• Useful for visualizing flow patterns.

Red

Toward

Blue

Away

Power Doppler

• Detects strength of Doppler signal, not direction.

• More sensitive to low flow or small vessels

• No info on flow direction or speed.

1. Radar Systems

2. Sonar Systems

3. Medical Imaging

4. Optical Doppler

Doppler Instrumentation

Cardiology

Assess valve diseases and heart chamber pressures.

Obstetrics

Monitor fetal circulation in umbilical artery or middle cerebral artery.

Vascular Imaging

Detect blood clots, stenosis, or arterial plaque.

Organ Perfusion

Check kidney, liver, or transplant viability.