Which color control was changed from image A to image B?

Which color control was changed from image A to image B?

• A. Gain
• B. Threshold
• C. PRF
• D. Transmit power

Answer: (C)

PRF controls how velocities are mapped into color in Doppler imaging. It sets the Nyquist limit, so changing PRF shifts the velocity range that can be displayed without aliasing. When PRF is adjusted, the same blood flow can appear with different colors or with altered aliasing, producing a noticeably different color display from one image to the next. The other controls don’t change the color map in the same way: increasing gain changes overall brightness of the color and grayscale, not the velocity encoding; threshold mainly decides which low-velocity signals are shown, affecting whether some color is present near the baseline; transmit power changes the strength of the echoes but not how velocities are color-encoded.

PRF controls how velocities are mapped into color in Doppler imaging. It sets the Nyquist limit, so changing PRF shifts the velocity range that can be displayed without aliasing. When PRF is adjusted, the same blood flow can appear with different colors or with altered aliasing, producing a noticeably different color display from one image to the next.

The other controls don’t change the color map in the same way: increasing gain changes overall brightness of the color and grayscale, not the velocity encoding; threshold mainly decides which low-velocity signals are shown, affecting whether some color is present near the baseline; transmit power changes the strength of the echoes but not how velocities are color-encoded.