Which term describes the phenomenon in which scatterers are much smaller than the wavelength, affecting backscatter?

• A. Rayleigh scattering
• B. Mie scattering
• C. Specular reflection
• D. Backscatter

Answer: (A)

Rayleigh scattering describes how very small targets interact with ultrasound waves. When scatterers are much smaller than the wavelength, the scattered field is dominated by those tiny targets (like red blood cells), and the backscattered signal becomes highly sensitive to frequency, producing characteristic speckle in the image. This contrasts with other regimes: Mie scattering occurs when scatterers are similar to the wavelength and has different angular distribution and frequency behavior; specular reflection comes from smooth, large boundaries and isn’t driven by tiny scatterers; backscatter is a general term for energy returned toward the transducer, not a size-dependent scattering regime.