When color Doppler is activated to maintain frame rate, which may be reduced in the underlying B-mode image?

• A. The number of focal zones
• B. The scan line density
• C. The frame averaging
• D. A and B

Answer: (D)

When color Doppler is turned on, keeping the display frame rate high often means trimming how much B-mode data the system has to process for each frame. Two key ways this happens are reducing the number of focal zones and lowering scan line density.

Fewer focal zones cut the time spent steering and focusing the beam at multiple depths, which speeds up frame construction but at the cost of reduced depth-specific focusing and lateral resolution. Lower scan line density reduces the number of lines sampled across the image, speeding up data acquisition and processing but producing a less detailed lateral image.

Frame averaging is a temporal averaging process that already smooths the image over time and can lower temporal resolution; to maintain frame rate with color Doppler, the system typically adjusts spatial parameters (fewer focal zones and lower line density) rather than rely on frame averaging. That’s why the best answer is that the frame rate-maintaining trade-offs involve A and B.