What are the differences between pulse-wave Doppler and continuous-wave Doppler, and when is each used?

What are the differences between pulse-wave Doppler and continuous-wave Doppler, and when is each used?

• A. PW samples velocity at a single site; CW measures velocity along the entire beam; CW is used for high-velocity flows but cannot localize depth
• B. PW samples velocity along the entire beam; CW samples velocity at a single site; CW is used for high-velocity flows but cannot localize depth
• C. PW uses color Doppler; CW uses spectral Doppler; used for measurement of valve area
• D. PW samples velocity at a single site; CW measures velocity along the entire beam; CW is used for high-velocity flows but cannot localize depth

Answer: (D)

Pulse-wave Doppler gathers velocity information from a single, user-selected location along the ultrasound beam. By sending a short pulse and listening for echoes from a specific depth (a sample gate), you get velocity at that precise site, which is essential for measuring flows like mitral inflow, LVOT, or across a valve at a known position. The trade-off is a limited velocity range set by the Nyquist limit; if the flow is too fast, aliasing can occur, distorting the measurement. Continuous-wave Doppler, in contrast, transmits and receives continuously along the entire beam path. It captures velocities from all points along that line, so there’s no depth localization. This allows accurate measurement of very high velocities without aliasing, which is why it’s preferred for high-velocity jets such as severe stenosis. The drawback is you don’t know exactly where along the beam the measured velocity originates. So, the best summary is: pulse-wave samples at a single depth, enabling depth localization with a limited velocity range; continuous-wave measures along the entire beam, yielding high-velocity measurements without aliasing but without depth information.

Pulse-wave Doppler gathers velocity information from a single, user-selected location along the ultrasound beam. By sending a short pulse and listening for echoes from a specific depth (a sample gate), you get velocity at that precise site, which is essential for measuring flows like mitral inflow, LVOT, or across a valve at a known position. The trade-off is a limited velocity range set by the Nyquist limit; if the flow is too fast, aliasing can occur, distorting the measurement.

Continuous-wave Doppler, in contrast, transmits and receives continuously along the entire beam path. It captures velocities from all points along that line, so there’s no depth localization. This allows accurate measurement of very high velocities without aliasing, which is why it’s preferred for high-velocity jets such as severe stenosis. The drawback is you don’t know exactly where along the beam the measured velocity originates.

So, the best summary is: pulse-wave samples at a single depth, enabling depth localization with a limited velocity range; continuous-wave measures along the entire beam, yielding high-velocity measurements without aliasing but without depth information.