Which of the following is a typical unit for amplitude of an ultrasound signal?

• A. Hz
• B. msec
• C. cm
• D. watts

Answer: (C)

Amplitude is the magnitude of the wave’s oscillation, essentially how far tissue particles move from their rest position. That displacement is a length, so its unit is a measure of distance. Among the given choices, centimeters reflect that displacement amplitude, making it the appropriate unit. The other options describe frequency (cycles per second), a time interval, and power (energy per time), which are properties unrelated to the magnitude of the oscillation itself. In ultrasound, while amplitude can also be discussed in terms of pressure or intensity, a displacement-based view uses length units like cm, fitting this question.