Used to fill in the missing data between scan lines in both gray scale and color Doppler.

• A. Demodulation
• B. Rejection
• C. Autocorrelation
• D. Interpolation

Answer: (D)

Interpolation is used to fill in the missing data between scan lines in both gray scale and color Doppler. In ultrasound, the image is built from discrete scan lines, and gaps can appear between them, especially with wider sectors or lower line density. Interpolation estimates the pixel values between those lines based on neighboring samples, creating a smoother grayscale image and a more continuous color Doppler map. This helps preserve spatial continuity and image quality without introducing new information. Other options perform different signal-processing roles: demodulation converts the RF signal to a form suitable for display, rejection removes unwanted signals or clutter, and autocorrelation is used to estimate Doppler velocity, not to fill spatial gaps.