Which factor can disturb the spectral window aside from stenosis?

• A. Increased Sample Volume
• B. Large Insonification Angles
• C. Use Of CW Instead Of PW
• D. Overall Doppler Gain

Answer: (C)

The concept being tested is the spectral window in pulsed-wave Doppler and how it depends on depth-selective sampling. In PW Doppler, a defined gate samples velocities from a specific depth, producing a spectrum with a visible, relatively narrow window (the area between the baseline and the spectral envelope). When conditions broaden the range of velocities within that gate, or when the gate isn’t used, this window can be disturbed.

Why switching to continuous-wave Doppler is the best answer: CW Doppler has no depth discrimination or range gate. It samples along the entire beam path continuously, so a depth-local spectrum with a clean spectral window cannot be formed in the same way as with PW. Because the spectral window depends on the presence of a range-gated, depth-specific signal, using CW effectively eliminates or disturbs that window.

Other factors can affect the appearance of the spectrum within PW (such as increasing the sample volume or changing the angle or gain), but they don’t fundamentally remove the spectral window in the same way that eliminating the range gate with CW Doppler does.