Infographics / Ultrasound Physics

Colour flow vs power Doppler imaging

Two-column comparison. Colour (flow) Doppler encodes mean blood velocity and direction: it shows toward and away flow, is angle-dependent (fails near 90 degrees), and can alias above the Nyquist limit. Power Doppler encodes the integrated Doppler signal power or amplitude: no direction and no velocity, but angle-independent, no aliasing, and more sensitive to slow or low flow while being more prone to flash motion artefact.

Colour Doppler versus power Doppler ultrasound Two-column comparison. Colour (flow) Doppler encodes mean blood velocity and direction: it shows toward and away flow, is angle-dependent (fails near 90 degrees), and can alias above the Nyquist limit. Power Doppler encodes the integrated Doppler signal power or amplitude: no direction and no velocity, but angle-independent, no aliasing, and more sensitive to slow or low flow while being more prone to flash motion artefact. Colour Doppler vs power Doppler — what each encodes Colour (flow) Doppler Power Doppler toward away flow present — any direction encodes mean velocity + direction encodes signal power (amplitude) Encoded quantity Mean velocity + direction Signal power (amplitude) Flow direction Yes — toward / away No Velocity value Yes No Angle (cosθ) Dependent — fails near 90° Independent — works near 90° Aliasing Can alias above PRF/2 None (no velocity scale) Slow / low flow Less sensitive More sensitive Flash / motion Less — wall-filtered More — motion-sensitive Both are pulsed-wave, range-gated; only colour Doppler wraps (aliases) because it displays velocity.
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