What physical concept allows us to determine the location of an interface by measuring the elapsed time between the transmitted pulsed ultrasound wave and the detected echo from that interface?

What physical concept allows us to determine the location of an interface by measuring the elapsed time between the transmitted pulsed ultrasound wave and the detected echo from that interface?

• A. Huygen's Principle
• B. Echo Ranging
• C. Snell's Law
• D. Doppler Effect

Answer: (B)

Time-of-flight measurement is used to locate an interface in pulsed ultrasound. A short ultrasound pulse travels to a boundary, reflects back as an echo, and the elapsed time from emission to detection is used to determine distance. Since the pulse makes a round trip, the distance to the interface is d = (c × t) / 2, where c is the speed of sound in the tissue. In soft tissue, c is about 1540 m/s, so you can convert the measured time into depth. This approach is called echo ranging (time-of-flight). The other concepts don’t directly yield depth from a single echo: Huygens’ principle describes wavefront propagation, Snell’s law governs refraction at boundaries, and the Doppler effect concerns frequency shifts due to motion.

Time-of-flight measurement is used to locate an interface in pulsed ultrasound. A short ultrasound pulse travels to a boundary, reflects back as an echo, and the elapsed time from emission to detection is used to determine distance. Since the pulse makes a round trip, the distance to the interface is d = (c × t) / 2, where c is the speed of sound in the tissue. In soft tissue, c is about 1540 m/s, so you can convert the measured time into depth. This approach is called echo ranging (time-of-flight). The other concepts don’t directly yield depth from a single echo: Huygens’ principle describes wavefront propagation, Snell’s law governs refraction at boundaries, and the Doppler effect concerns frequency shifts due to motion.