What is the primary purpose of pulsing in order to determine depth?

• A. The transducer overheats
• B. The depth of the interface from which the echo originated can be determined
• C. The crystal breaks
• D. Lateral resolution improves

Answer: (B)

Pulsing sends a brief ultrasound burst into the tissue and waits for echoes. The time between emission and reception of those echoes is used, with the known speed of sound in tissue, to calculate how far away the reflecting interface is. Since the sound travels to the interface and back, depth is half the round-trip distance: depth ≈ (speed of sound × time) / 2. This is how the depth of structures is determined on the image. The other options refer to potential risks or different performance aspects (overheating, crystal damage, or lateral resolution), which are not the purpose of pulsing for depth measurement.