The propagation speed of ultrasound in the AIUM test object is:

• A. 1 m/s
• B. 1.54 mm/microsec
• C. 1.54 m/s
• D. 1 km/s

Answer: (B)

The value being tested is how fast ultrasound travels through the AIUM test object, which is a medium with a known propagation speed. In soft-tissue–like materials used for ultrasound phantoms, the speed of sound is typically about 1540 meters per second. In practical units used in clinical ultrasound, that speed is expressed as roughly 1.54 millimeters per microsecond. Therefore, the correct option is the one that states 1.54 mm/µs, since 1.54 mm/µs equals 1540 m/s. The other choices are not consistent with the standard speed for these phantoms and would not yield the expected timing or depth calculations.