If you’re new to ultrasound, an image may look like nothing more than a swirling array of grey tones on the screen. Interpretation requires an understanding of anatomy and physiology, but also of how ultrasound technology functions.
Consider the sonar produced by a bat in flight. The bat emits high frequency sounds, which then bounce off of objects in its proximity and return to the bat. The animal uses the strength, direction, and timing of the returning sound to determine where those objects are and to avoid a collision.