Which Doppler modality provides velocity information but does not provide depth information?

Which Doppler modality provides velocity information but does not provide depth information?

• A. Color Doppler
• B. Power Doppler
• C. Pulsed-wave Doppler
• D. Continuous-wave Doppler

Answer: (D)

The key idea is that depth localization requires range gating, while velocity information can be obtained without it in certain setups. Continuous-wave Doppler transmits continuously and receives signals at the same time, so Doppler shifts are measured along the entire beam path rather than at a specific depth. Because there’s no range resolution, you can detect how fast something is moving along the line of sight, but you can’t tell exactly where along that path the measurement comes from. That’s why this modality provides velocity information but not depth information. By contrast, pulsed-wave Doppler uses short pulses and time-of-flight to pinpoint a specific depth (range gate), so you get velocity data tied to a particular location. Color Doppler wraps velocity information over a 2D image, linking color to precise spatial locations in the image, which provides depth context. Power Doppler shows the presence and strength of flow across a region, again mapped to depth in the image, though it doesn’t measure velocity.

The key idea is that depth localization requires range gating, while velocity information can be obtained without it in certain setups.

Continuous-wave Doppler transmits continuously and receives signals at the same time, so Doppler shifts are measured along the entire beam path rather than at a specific depth. Because there’s no range resolution, you can detect how fast something is moving along the line of sight, but you can’t tell exactly where along that path the measurement comes from. That’s why this modality provides velocity information but not depth information.

By contrast, pulsed-wave Doppler uses short pulses and time-of-flight to pinpoint a specific depth (range gate), so you get velocity data tied to a particular location. Color Doppler wraps velocity information over a 2D image, linking color to precise spatial locations in the image, which provides depth context. Power Doppler shows the presence and strength of flow across a region, again mapped to depth in the image, though it doesn’t measure velocity.