In color Doppler imaging, what is a color packet?

• A. A single acoustic beam
• B. A color map update
• C. Multiple acoustic beams transmitted to acquire samples at a location
• D. A spectral sample

Answer: (C)

A color packet is the ensemble of Doppler samples acquired at a single location by transmitting multiple acoustic beams in quick succession. This group of beams provides enough data to estimate the Doppler frequency shift at that point, which is then converted into the color display. Using several beams (an ensemble) improves the reliability of velocity estimation and noise suppression, but it increases the time needed to update the color map, lowering frame rate. A single acoustic beam wouldn’t yield enough information for reliable Doppler estimation. A color map update refers to refreshing the color overlay, not how the data at each location are acquired. A spectral sample is the Doppler waveform from one location, not the color-encoded ensemble.