Shadowing behind the lateral borders of a cyst is produced by which source?

Shadowing behind the lateral borders of a cyst is produced by which source?

• A. Redirection of the sound beam at an interface with different propagation speeds and a curved surface.
• B. Bending of the sound beam due to different media propagation speeds.
• C. Increased attenuation of the sound beam at the borders of the cyst.
• D. Lateral misregistration of the cyst due to a multipath artifact.

Answer: (B)

Shadowing along the lateral borders of a cyst is due to refraction—the bending of the ultrasound beam when it passes from one medium to another with a different propagation speed. The cyst wall is curved, so the rays hitting the boundary are refracted, often bending away from the edge. This shifts the beam away from behind the border, producing a shadow in that region. While attenuation and other artifacts can affect imaging, the distinct edge shadow at a curved boundary most directly results from beam bending from the speed difference between tissues.

Shadowing along the lateral borders of a cyst is due to refraction—the bending of the ultrasound beam when it passes from one medium to another with a different propagation speed. The cyst wall is curved, so the rays hitting the boundary are refracted, often bending away from the edge. This shifts the beam away from behind the border, producing a shadow in that region. While attenuation and other artifacts can affect imaging, the distinct edge shadow at a curved boundary most directly results from beam bending from the speed difference between tissues.