Which parameter describes the center frequency of the emitted spectrum in pulsed-wave ultrasound?

• A. Bandwidth
• B. Wavelength
• C. Center frequency
• D. Q-factor

Answer: (C)

In pulsed-wave ultrasound, the emitted signal is a short burst that contains a range of frequencies. The energy isn’t confined to a single frequency; it clusters around a central value. That central value is what we mean by the center frequency—it's the frequency around which the spectrum’s energy is most concentrated and serves as the reference for describing the transmitted signal.

Bandwidth describes how wide that spectrum is—the spread of frequencies present—rather than the central value itself. Wavelength is linked to frequency through the speed of sound in the medium, but it doesn’t describe the spectrum’s central content. The Q-factor, meanwhile, describes how selective or sharp the resonance is, essentially the ratio of center frequency to bandwidth, not the central frequency alone.