Spectral analysis is used to:

• A. Determine the distribution and magnitude of frequency shifts in the reflected Doppler signal
• B. Eliminate aliasing from the reflected signal
• C. Color-encode the Doppler frequency shift
• D. Eliminate low-frequency shifts from the display

Answer: (A)

Spectral analysis examines the frequency content of a Doppler signal to reveal how fast and how broadly motion is shifting the frequency. By converting the time-domain Doppler signal into a spectrum, you can see the distribution of Doppler shifts and their magnitudes at a given moment, which corresponds to the different velocities present in the flow and how strongly they contribute. This is exactly what is meant by determining the distribution and magnitude of frequency shifts in the reflected Doppler signal.

Aliasing isn’t something spectral analysis cures by itself; it arises from sampling limits. To avoid aliasing you’d change the sampling rate or the PRF, not rely on spectral analysis to fix it. Color-encoding the Doppler shift is a visualization approach (color Doppler) separate from the spectral decomposition. Eliminating low-frequency shifts would be a filtering choice, not the primary purpose of spectral analysis, which is to reveal the frequency content rather than remove specific components.