ARDMS Ultrasound Physics & Instrumentation Practice Exam

Which unit of measurement is appropriate for propagation speed in ultrasound?

1. Centimeters per second (cm/s)

2. Millimeters per microsecond (mm/μs)

3. Hertz (Hz)

4. Decibels (dB)

The correct answer is: Millimeters per microsecond (mm/μs)

Propagation speed in ultrasound refers to how fast the ultrasound wave travels through a medium. This speed is commonly measured in millimeters per microsecond (mm/μs). In the context of ultrasound, this unit is particularly useful because it allows precise measurements that correspond well to the scales typically encountered in medical imaging. For instance, the speed of sound in soft tissue is generally around 1540 meters per second, which translates to 1.54 mm/μs. This unit captures the rapid propagation of sound waves effectively and aligns with the dimensions of the structures being evaluated in ultrasound imaging. Other units provided in the options serve different purposes: centimeters per second (cm/s) and Hertz (Hz) measure different phenomena. Decibels (dB) is a unit used to express the intensity of sound or the gain of signal strength, not the speed of propagation. Thus, measuring propagation speed in mm/μs is both conventional and useful for understanding the behavior of ultrasound waves in medical applications.