Ace the Ultrasound Physics 2026 Challenge – Dive Into Waves of Success!

Scattering in ultrasound depends on how the size of the structures compares to the wavelength. When the boundary is smooth and its dimensions exceed the wavelength, the wave reflects in a single preferred direction—this is specular reflection. Vessel walls act like smooth interfaces that are larger than the ultrasound wavelength, so you see a clear, specular echo from them.

When there are many tiny particles much smaller than the wavelength, each scatters in various directions and the backscatter is diffuse. This Rayleigh-type scattering from numerous small scatterers builds up the speckle you see in the image. Red blood cells are only a few micrometers across, far smaller than typical tissue wavelengths, so they produce this diffuse backscatter.

So the best description is: specular scattering from smooth surfaces larger than the wavelength (vessel wall), and Rayleigh scattering from many small scatterers smaller than the wavelength (red blood cells).