What artifact is caused by random interference of echoes from tissue microstructure, producing a grainy appearance?

• A. Shadowing
• B. Speckle
• C. Ring down
• D. Enhancement

Answer: (B)

Speckle is the granular, grainy texture you see on ultrasound images. It comes from random interference of echoes bouncing off many tiny tissue scatterers within each resolution element. The different echoes combine with varying phases, creating bright and dark spots that give that grainy look. This texture is not from a distinct structure but from how the echoes interfere inside the tissue.

This matches the description of a grainy appearance caused by random interference. Other artifacts have different causes: shadowing appears as a dark area beyond a strongly attenuating structure, enhancement appears as a brighter region beyond a low-attenuation lesion like a cyst, and ring-down is a specific reverberation from gas bubbles. Speckle is intrinsic to the image and can be mitigated with techniques like spatial or frequency compounding.