The reduction of echo amplitude from reflectors behind a strong attenuating structure is known as:

• A. Shadowing
• B. Signal to Noise Ratio
• C. Spatial Compounding
• D. A-Mode

Answer: (A)

Shadowing happens when a strongly attenuating structure, such as bone, calcifications, or a dense implant, absorbs or scatters most of the ultrasound energy. Because less energy reaches deeper reflectors, the echoes from those behind-the-structure reflectors are markedly weaker, producing a dark region or shadow just beyond the structure. This posterior shadowing is a telltale sign of a dense object and can obscure deeper anatomy. The other terms describe different ideas: signal-to-noise ratio is about the overall balance of true signal versus background noise, spatial compounding is a technique that combines images from multiple angles to reduce artifacts, and A-mode is an old one-dimensional display of echoes rather than a reflection of this attenuation effect.