Which term describes red blood cells in the context of Doppler scatterers due to their small size?

Which term describes red blood cells in the context of Doppler scatterers due to their small size?

• A. Mie scatterers
• B. Rayleigh scatterers
• C. Specular reflectors
• D. Absorbers

Answer: (B)

In Doppler ultrasound, how particles scatter sound depends on their size relative to the acoustic wavelength. Red blood cells are about 6–8 micrometers in diameter, which is much smaller than the ultrasound wavelength at typical Doppler frequencies (for example, at 5–10 MHz in tissue, wavelengths are roughly 150–300 micrometers). Because the cells are so small compared with the wavelength, they fall into the Rayleigh scattering regime. In this regime, scatter is produced by many tiny particles in all directions, and the scattering characteristics scale with particle size in a specific way that matches what red blood cells do, making Rayleigh scatterers the best description. Mie scatterers would apply if the particles were about the same size as the wavelength; specular reflectors describe large, smooth surfaces that reflect like mirrors; absorbers primarily reduce energy rather than scatter it. The Doppler signal arises from the motion of these Rayleigh scatterers (the red blood cells) causing a frequency shift in the backscattered ultrasound.

In Doppler ultrasound, how particles scatter sound depends on their size relative to the acoustic wavelength. Red blood cells are about 6–8 micrometers in diameter, which is much smaller than the ultrasound wavelength at typical Doppler frequencies (for example, at 5–10 MHz in tissue, wavelengths are roughly 150–300 micrometers). Because the cells are so small compared with the wavelength, they fall into the Rayleigh scattering regime. In this regime, scatter is produced by many tiny particles in all directions, and the scattering characteristics scale with particle size in a specific way that matches what red blood cells do, making Rayleigh scatterers the best description.

Mie scatterers would apply if the particles were about the same size as the wavelength; specular reflectors describe large, smooth surfaces that reflect like mirrors; absorbers primarily reduce energy rather than scatter it. The Doppler signal arises from the motion of these Rayleigh scatterers (the red blood cells) causing a frequency shift in the backscattered ultrasound.