What term is used to describe the reduction in the intensity of sound as it propagates through tissue?

• A. Diffraction
• B. Absorption
• C. Attenuation
• D. Refraction

Answer: (C)

Attenuation is the reduction in sound intensity as it propagates through tissue. As the ultrasound wave travels, energy is lost due to several processes: absorption, where the wave’s energy is converted to heat within the tissue; scattering, where energy is redirected out of the main beam; and some energy is reflected at interfaces between tissues. All of these factors combine to decrease the forward-going intensity. This is why higher-frequency beams attenuate more rapidly, limiting how deeply we can image. In practice, attenuation is described by how much energy is lost per unit distance, often quantified with an attenuation coefficient. Absorption is a big part of this overall loss, but attenuation refers to the total decrease in intensity, not just a single mechanism.