What does the Doppler spectral display depict?

What does the Doppler spectral display depict?

• A. Depth to each vessel
• B. Volume flow rate
• C. Relative signal power at each frequency in the Doppler signal
• D. Transmit frequency

Answer: (C)

The Doppler spectral display conveys how moving blood within the sampled volume is distributed across different velocities. It does this by plotting the relative power or amplitude of the Doppler signal against Doppler frequency shifts. Since the Doppler shift is proportional to the blood’s velocity along the beam, each frequency in the spectrum corresponds to a velocity, and the height of the spectrum at that frequency shows how much blood is moving at that velocity. Positive shifts indicate flow toward the transducer, negative shifts indicate flow away, and the shape of the spectrum reveals peak velocity and spectral broadening. This view isn’t about depth to vessels (that comes from the B-mode or color positioning), and it isn’t a direct measure of volume flow rate (you’d need vessel area and a velocity profile to calculate that). It also doesn’t display the transmit frequency itself—the spectrum reflects the Doppler shifts produced by motion, not the transducer’s fundamental frequency.

The Doppler spectral display conveys how moving blood within the sampled volume is distributed across different velocities. It does this by plotting the relative power or amplitude of the Doppler signal against Doppler frequency shifts. Since the Doppler shift is proportional to the blood’s velocity along the beam, each frequency in the spectrum corresponds to a velocity, and the height of the spectrum at that frequency shows how much blood is moving at that velocity. Positive shifts indicate flow toward the transducer, negative shifts indicate flow away, and the shape of the spectrum reveals peak velocity and spectral broadening.

This view isn’t about depth to vessels (that comes from the B-mode or color positioning), and it isn’t a direct measure of volume flow rate (you’d need vessel area and a velocity profile to calculate that). It also doesn’t display the transmit frequency itself—the spectrum reflects the Doppler shifts produced by motion, not the transducer’s fundamental frequency.