These two images show a Pseudoaneurysm sac. What control was optimized in image B to allow the color to write over the gray-scale echoes?

These two images show a Pseudoaneurysm sac. What control was optimized in image B to allow the color to write over the gray-scale echoes?

• A. PRF
• B. Wall filter
• C. Gain
• D. Threshold

Answer: (D)

Color Doppler overlay on gray-scale tissue echoes is controlled by the display threshold for Doppler signals. Lowering this threshold lets more Doppler signals—especially weaker flow often seen in a pseudoaneurysm sac—be displayed as color. With the threshold reduced, the color information can write over the gray-scale echoes, making the flow in the sac visible as colored pixels atop the grayscale image. The other controls affect different aspects: PRF changes the velocity range, wall filter removes low-velocity tissue signals, and gain amplifies echoes, but none specifically govern the displayed sensitivity of color over gray-scale in this way.

Color Doppler overlay on gray-scale tissue echoes is controlled by the display threshold for Doppler signals. Lowering this threshold lets more Doppler signals—especially weaker flow often seen in a pseudoaneurysm sac—be displayed as color. With the threshold reduced, the color information can write over the gray-scale echoes, making the flow in the sac visible as colored pixels atop the grayscale image. The other controls affect different aspects: PRF changes the velocity range, wall filter removes low-velocity tissue signals, and gain amplifies echoes, but none specifically govern the displayed sensitivity of color over gray-scale in this way.