What artifact occurs when there is a change in the speed of sound in the medium?

The artifact that occurs when there is a change in the speed of sound in the medium is known as the speed error artifact. This artifact manifests when ultrasound waves travel through media with different acoustic velocities, leading to a misplacement of the structures in the image.

In normal circumstances, ultrasound assumes a speed of sound within soft tissues to be approximately 1540 m/s. However, if the medium has a different speed of sound, such as in areas with varying densities or in specific tissues, the ultrasound machine may inaccurately calculate the depth of the echo returns. This results in either an appearance of structures being positioned inaccurately or possibly distorting their size.

For example, if the sound speed is increased, the structures may appear closer than they truly are, while a decreased speed can make them appear farther away. Thus, understanding the relationship between sound speed and imaging is crucial to interpreting ultrasound images accurately.