What is the commonly used average speed of sound in soft tissue for diagnostic ultrasound?

• A. 1700
• B. 1540
• C. 1490
• D. 1600

Answer: (B)

When we convert the time it takes for a sound pulse to travel to a reflector and back into a depth, we rely on the speed of sound in the tissue. For diagnostic ultrasound, soft tissue is commonly approximated with a speed of about 1540 meters per second. This value is used as the practical average because most soft tissues fall near this speed, which keeps depth measurements and image geometry consistent across exams. The basic relation is d = (c × t)/2, where t is the round-trip time and c is the speed of sound. While actual tissues vary (fat and fluids around 1450–1490 m/s, muscle closer to 1540–1580 m/s, bone much higher), 1540 m/s provides a reliable standard. The other numbers listed do not reflect the typical soft-tissue average used in practice.