Which of the following statements best describes a characteristic of frequency in ultrasound?

• A. It is determined by the medium.
• B. It is the number of cycles per second.
• C. It is the speed of light.
• D. It is unaffected by the transducer.

Answer: (B)

Frequency in ultrasound is the number of cycles that occur each second, measured in hertz. This value is set by the transducer’s electrical drive, so the emitted frequency is determined by the transducer rather than the tissue. As the wave travels through the medium, its frequency remains the same—the medium only affects how fast the wave travels and what its wavelength is, via the relationship v = f·λ. The speed of light is not involved in ultrasound. So, describing frequency as the number of cycles per second is the most accurate characterization.