A broadening of the spectrum of frequencies reflected back to the transducer describes what term?

• A. Doppler shift
• B. Aliasing
• C. Spectral broadening
• D. Attenuation

Answer: (C)

The essential idea is that when there are multiple velocities within the sampled region or turbulent flow, the range of Doppler frequency shifts becomes wider. This distribution of velocities causes the reflected frequencies to spread, so the Doppler spectrum broadens instead of showing a sharp, single peak. In spectral Doppler, a broader spectrum indicates more complex or disturbed flow, such as turbulence or flow in small vessels, where scatterers move at different speeds. The other terms describe different phenomena: Doppler shift is the basic change in frequency due to motion, aliasing occurs when the sampling rate isn’t high enough to capture fast flows, and attenuation is the loss of signal strength with depth. Thus, the description fits spectral broadening.