ARDMS SPI Pulsed-Wave and CW Doppler 3 — Questions and Answers
Question 1: What is the effect of increasing the pulse repetition frequency (PRF) on maximum detectable depth in PW Doppler?
- Maximum depth increases
- Maximum depth decreases because less time is allowed for echoes to return from deep structures (Correct answer)
- Maximum depth is unaffected by PRF
- Maximum depth doubles
Correct 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.
Question 2: In spectral Doppler, what does the spectral broadening of the waveform indicate?
- A homogeneous laminar flow profile
- A wide range of velocities within the sample volume, often indicating turbulence or disturbed flow (Correct answer)
- Instrument malfunction
- Very low wall filter settings
Correct 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.
Question 3: Which statement correctly describes range ambiguity artifact in PW Doppler?
- It occurs when the sample gate is placed incorrectly
- 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 (Correct answer)
- It is caused by side lobe interference
- It only occurs with color Doppler, not spectral Doppler
Correct 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.
Question 4: The wall filter (high-pass filter) in Doppler ultrasound is used primarily to:
- Remove high-velocity arterial signals
- Eliminate low-frequency signals from slow-moving vessel walls and tissue clutter (Correct answer)
- Increase the Nyquist limit
- Reduce acoustic noise from the transducer
Correct 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.
Question 5: When performing angle correction for Doppler velocity calculations, ARDMS guidelines recommend keeping the Doppler angle at:
- 90° for the most accurate measurement
- Greater than 75° for best sensitivity
- 60° or less to minimize angle-related velocity errors (Correct answer)
- Exactly 45° at all times
Correct 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°.
Question 6: In a normal triphasic arterial waveform seen in peripheral arteries, which component represents the brief reverse-flow phase?
- The first forward peak (systolic peak)
- The second component — a brief dip below the baseline (Correct answer)
- The third component — a small forward diastolic peak
- The spectral window
Correct 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.
Question 7: Which of the following best explains why CW Doppler is NOT affected by aliasing?
- CW Doppler uses a lower transmit frequency
- CW Doppler continuously transmits and receives without a PRF limitation, so there is no Nyquist limit constraint (Correct answer)
- CW Doppler applies a higher wall filter
- CW Doppler uses phase-quadrature detection
Correct 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.
ARDMS SPI Pulsed-Wave and CW Doppler 3
What is the effect of increasing the pulse repetition frequency (PRF) on maximum detectable depth in PW Doppler?