Sound waves in the lung attenuate dramatically because of which mechanisms?

Sound waves in the lung attenuate dramatically because of which mechanisms?

• A. Reflection and Refraction
• B. Diffraction and Reflection
• C. Scattering and Refraction
• D. Scattering and Absorption

Answer: (D)

Sound waves attenuate in the lung primarily because of scattering and absorption. The lung is highly inhomogeneous with countless air-tissue interfaces at many scales. These interfaces break up the forward wave, sending energy in many directions, so less energy remains along the original path. At the same time, the tissue and fluids absorb part of the acoustic energy, converting it into heat through viscous and thermal losses. This combination—energy being scattered away from the forward beam and energy being absorbed by the tissue—causes the dramatic attenuation. Reflections and refractions do occur at interfaces, but they don’t remove as much energy from the forward path as scattering plus absorption, and diffraction mainly redistributes energy rather than causing the large, net loss seen here.

Sound waves attenuate in the lung primarily because of scattering and absorption. The lung is highly inhomogeneous with countless air-tissue interfaces at many scales. These interfaces break up the forward wave, sending energy in many directions, so less energy remains along the original path. At the same time, the tissue and fluids absorb part of the acoustic energy, converting it into heat through viscous and thermal losses. This combination—energy being scattered away from the forward beam and energy being absorbed by the tissue—causes the dramatic attenuation. Reflections and refractions do occur at interfaces, but they don’t remove as much energy from the forward path as scattering plus absorption, and diffraction mainly redistributes energy rather than causing the large, net loss seen here.