Which type of reflections occur when the wave strikes a large, smooth surface at normal incidence?

• A. Specular
• B. Backscatter
• C. Speckle
• D. Diffuse

Answer: (A)

Specular reflection comes from a surface that is large and smooth compared with the ultrasound wavelength. When the wave strikes perpendicularly (normal incidence), the incident angle is 0 degrees relative to the surface normal, so the reflection travels back toward the transducer with the same angle it arrived—producing a clear, mirror-like echo. This coherent, well-defined reflection is what you expect from a smooth, flat interface.

Backscatter refers to energy returning from many small, irregular scatterers in tissue and tends to be diffuse rather than mirror-like. Speckle is the grainy interference pattern created by the combined echoes from numerous scatterers within a resolution cell. Diffuse reflection comes from rough surfaces that scatter energy in many directions. None of these match the clean, mirror-like return produced by a large smooth surface at normal incidence.