Ultrasound Physics II Practice Exam

In ultrasound, the time delay is the round-trip travel time of the sound wave: the pulse goes to a structure and back to the transducer. Since the distance the wave must cover is twice the one-way distance (there and back), the delay t is related by t ≈ 2d / c, where c is the speed of sound in tissue (about 1540 m/s). With the speed of sound treated as roughly constant, a longer time delay means a larger distance to the reflector. Conversely, a shorter time delay means a closer structure. So the time delay corresponds to more distance.