Which structure among the following is a Rayleigh scatterer?

Which structure among the following is a Rayleigh scatterer?

• A. Renal capsule
• B. Arterial wall
• C. Red blood cell
• D. Bowel gas

Answer: (C)

Rayleigh scattering happens when the scattering centers are much smaller than the wavelength of the incident wave. In diagnostic ultrasound, the wavelength in soft tissue at common frequencies is on the order of a few tenths of a millimeter. Red blood cells are about 6–8 micrometers in diameter, which is far smaller than the ultrasound wavelength, so they behave as Rayleigh scatterers. The other structures are larger than the wavelength, so they scatter light or sound by different mechanisms (Mie or geometric scattering) rather than Rayleigh. Bowel gas contains air pockets with a range of sizes, many not small compared to the wavelength, so their scattering isn’t Rayleigh either.

Rayleigh scattering happens when the scattering centers are much smaller than the wavelength of the incident wave. In diagnostic ultrasound, the wavelength in soft tissue at common frequencies is on the order of a few tenths of a millimeter. Red blood cells are about 6–8 micrometers in diameter, which is far smaller than the ultrasound wavelength, so they behave as Rayleigh scatterers.

The other structures are larger than the wavelength, so they scatter light or sound by different mechanisms (Mie or geometric scattering) rather than Rayleigh. Bowel gas contains air pockets with a range of sizes, many not small compared to the wavelength, so their scattering isn’t Rayleigh either.