Which is most likely to create Rayleigh Scattering?

• A. Red Blood Cells
• B. Muscle
• C. Scattering
• D. Bone

Answer: (A)

Rayleigh scattering occurs when the scatterers are much smaller than the wavelength of the ultrasound. In diagnostic imaging, red blood cells—about 6–8 micrometers in diameter—are tiny compared with typical wavelengths in soft tissue (on the order of a tenth to a millimeter at common imaging frequencies). Because they are so small relative to the wavelength, they act as many individual, tiny scatterers that produce backscattered echoes with Rayleigh-type behavior, contributing to the speckle pattern seen in ultrasound images.

Larger structures, like muscle fibers or bone, are bigger than the wavelength, so they scatter sound in different ways (Mie or mostly directional/strong reflections) rather than Rayleigh scattering. The option “scattering” is too vague to be specific to Rayleigh, which is defined by the relative size of scatterers to the wavelength.

So, red blood cells are the most likely to create Rayleigh scattering.