Echo signals displayed on the monitor arise from which interactions?

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

Answer: (C)

Echo signals on the monitor come from sound waves bouncing back after meeting interfaces or structures in the tissue. When a pulse encounters a boundary with a different acoustic impedance, part of its energy is reflected toward the transducer, creating a clear echo that indicates a boundary. In addition, many small or rough structures scatter energy in multiple directions, and some of that scattered energy returns to the transducer as weaker, diffuse echoes. The combination of these returned reflections and backscatter forms the image you see.

Refraction and diffraction influence how the beam travels and spreads but do not primarily generate the echoes that are displayed. Refraction changes direction when speeds differ across interfaces, and diffraction affects beam spread, but the detectable echoes mainly arise from reflections and scattering.