When can scattering occur?
If the boundary between two media has irregularities (with a size similar to or a bit smaller than the pulse's wavelength), then the wave may be chaotically redirected in all directions

What is Specular Reflection?
Reflections from a smooth reflector (mirror) are specular and return in one direction.

Under what conditions does Rayleigh Scattering occur?
If a reflector is much smaller than the wavelength of sound, sound is uniformly distributed in all directions (omnidirectional).  Higher frequency sound undergoes more Rayleigh scattering.  A red blood cell is a Rayleigh scatterer.

What is the Attenuation Coefficient in soft tissue?
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In soft tissue, the attenuatio coefficient (dB/cm) is approximately one-half of the frequency (MHz).

0.5dB/cm/MHz
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