Which term best describes the mechanism that reduces signal strength with distance in ultrasound?

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

Answer: (A)

Attenuation describes the decrease in ultrasound signal strength as it propagates through tissue. As the wave travels, energy is lost through absorption—where tissue converts part of the energy into heat—and scattering, which redirects energy away from the forward beam. The beam also spreads over a larger area with distance, so the intensity at a given depth drops. Together, these processes explain why the signal weakens as it travels deeper. Refraction would change direction at boundaries, not the overall loss of amplitude. Diffraction affects beam shape around obstacles but isn’t the primary distance-related loss. Reflection involves energy bouncing back at interfaces, not the forward attenuation with depth.