The standard speed of sound used to calculate distances in ultrasound tissue phantoms is closest to which value?

• A. 1500 m/s
• B. 1540 m/s
• C. 1600 m/s
• D. 1400 m/s

Answer: (B)

In ultrasound, distances are determined from the time it takes for a sound pulse to travel to a reflector and back. Because the pulse makes a round trip, the depth is calculated as depth = (c × t) / 2, where c is the speed of sound in the medium and t is the measured round-trip time. For tissue phantoms, a standard reference speed is used to keep measurements consistent, and the typical value for soft tissue is 1540 m/s. This chosen speed reflects the average velocity of ultrasound through soft tissues and provides a common baseline for calibrating phantoms and comparing results across equipment. Other numbers (like 1500, 1600, or 1400 m/s) correspond to different materials or tissues and would yield different depth estimations, so they’re not the standard for soft-tissue phantoms.