Medical ultrasound utilises the pulse-echo principle to construct a two-dimensional image of anatomical structures within a patient.

This is essentially the same principle used by bats to catch insects through echo-location.

Ultrasound is not emitted continuously from the transducer, as there would be no way of knowing how long a wave had been travelling once it returned to the transducer. Instead, transducers oscillate between emitting a pulse of ultrasound, and then in the pause that follows, the time that elapses for the echoes to be detected is measured.