Pulsed-Wave and CW Doppler Flashcards

What is the effect of increasing the pulse repetition frequency (PRF) on maximum detectable depth in PW Doppler?

Answer: Maximum depth decreases because less time is allowed for echoes to return from deep structures

Increasing PRF sends pulses more frequently, leaving less time for echoes from deep structures to return before the next pulse is sent, which reduces the maximum detectable depth.

In spectral Doppler, what does the spectral broadening of the waveform indicate?

Answer: A wide range of velocities within the sample volume, often indicating turbulence or disturbed flow

Spectral broadening — filling in of the spectral window — indicates that many different velocities exist within the sample volume simultaneously, which is characteristic of turbulent or disturbed flow.

Which statement correctly describes range ambiguity artifact in PW Doppler?

Answer: It occurs when echoes from a previous pulse return after the next pulse has been transmitted, causing signals from two depths to be displayed simultaneously

Range ambiguity occurs when a high PRF is used and echoes from deep structures return after the next pulse is already transmitted, causing signals from multiple depths to be displayed as if from the gate location.

The wall filter (high-pass filter) in Doppler ultrasound is used primarily to:

Answer: Eliminate low-frequency signals from slow-moving vessel walls and tissue clutter

The wall filter removes low-frequency, high-amplitude Doppler signals produced by slow-moving vessel walls and surrounding tissues (clutter) so that weaker signals from blood flow can be displayed.

When performing angle correction for Doppler velocity calculations, ARDMS guidelines recommend keeping the Doppler angle at:

Answer: 60° or less to minimize angle-related velocity errors

Angles ≤60° are recommended because small errors in angle estimation cause proportionally larger velocity errors as the angle increases, especially above 60°.

In a normal triphasic arterial waveform seen in peripheral arteries, which component represents the brief reverse-flow phase?

Answer: The second component — a brief dip below the baseline

The second component of the triphasic waveform is a brief reversal of flow below the baseline that occurs in early diastole due to the elastic recoil of the arterial wall.

Which of the following best explains why CW Doppler is NOT affected by aliasing?

Answer: CW Doppler continuously transmits and receives without a PRF limitation, so there is no Nyquist limit constraint

Because CW Doppler continuously transmits on one element and receives on another with no pulsed repetition interval, there is no PRF and therefore no Nyquist limit to cause aliasing.