Which tissue feature typically produces specular scattering in ultrasound imaging?

• A. Red blood cells.
• B. Smooth vessel walls.
• C. Bone trabeculae.
• D. Diffuse scatterers.

Answer: (C)

Specular scattering occurs when the ultrasound wave meets a large, smooth boundary relative to the wavelength, so energy reflects in a single, mirror-like direction. Bone trabeculae provide organized, plate-like interfaces with relatively smooth surfaces over distances large compared to the wavelength, allowing the beam to reflect coherently and produce a bright, specular echo. Red blood cells are much smaller than the wavelength and are randomly arranged, causing backscatter in many directions and creating a speckled, diffuse signal rather than a sharp reflection. Diffuse scatterers generate this grainy texture because they break up the wave in multiple directions, not in one focused reflection. Smooth vessel walls are indeed a smooth boundary, but the strong, well-defined reflections from the organized bone trabecular interfaces are a classic source of specular scattering in ultrasound.