_____ and ____ give rise to the echoes signals that are displayed on the monitor.

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

Answer: (C)

In ultrasound imaging, the monitor shows echoes that come back to the transducer after the emitted pulse interacts with tissue. The two main ways those back signals arise are reflection and scattering. Reflection occurs at interfaces where the acoustic impedance changes, sending part of the energy back toward the transducer. Scattering happens when the wave encounters small inhomogeneities or rough surfaces, producing many backscatter echoes that contribute to the image.

Refraction changes the direction of the transmitted wave as it enters a new medium, but it doesn’t by itself create the strong backecho that the transducer detects. Diffraction describes how waves bend around obstacles but isn’t the primary source of the returned echo signals in standard imaging. So the combination of reflection and scattering best explains the echoes displayed on the monitor.