Which statement defines ultrasound frequency?

• A. Sound with a frequency greater than 20,000 cycles per second
• B. Light waves with high frequency
• C. A type of microwave radiation
• D. A thermal imaging technique using infrared

Answer: (A)

Ultrasound frequency is about the number of cycles a sound wave completes each second, and it refers to sounds that are too high to be heard. The boundary between sound we can hear and ultrasound is roughly 20,000 cycles per second (20 kHz). So anything above that is defined as ultrasound. In practice, ultrasound devices for therapy or imaging use frequencies in the megahertz range, but the defining idea is simply a frequency greater than the audible limit.

The other options describe waves or techniques that are not sound waves: light waves and microwaves are electromagnetic radiation, and infrared imaging uses infrared radiation for heat sensing, not sound.