What is the velocity of sound in human soft tissue at 37°C (approximately)?

• A. 1.54 mm/µs
• B. 0.154 mm/µs
• C. 15.4 mm/µs
• D. 154 mm/µs

Answer: (A)

The key idea is the typical speed of ultrasound in soft tissue at body temperature. In soft tissue, sound travels at about 1540 meters per second, which converts to roughly 1.54 millimeters per microsecond. This is the figure used in clinical ultrasound to convert time delays into distances.

To see the conversion: 1540 m/s equals 1,540,000 mm/s. Since there are 1,000,000 microseconds in a second, that becomes 1.54 mm per microsecond. The other options are off by factors of 10 to 100 and don’t match the known soft-tissue speed.