ARDMS SPI Pulsed-Wave and CW Doppler 4 — Questions and Answers
Question 1: What is the primary purpose of the fast Fourier transform (FFT) in spectral Doppler ultrasound?
- To generate color-flow images
- To convert the raw Doppler audio signal into a frequency spectrum displayed over time (Correct answer)
- To correct for angle errors automatically
- To increase the pulse repetition frequency
Correct answer: To convert the raw Doppler audio signal into a frequency spectrum displayed over time
The FFT mathematically decomposes the complex Doppler signal into its individual frequency components, which are then displayed as a spectrum of velocities over time on the spectral waveform.
Question 2: A sonographer notes that the peak systolic velocity (PSV) appears falsely elevated when the sample volume is placed near a vessel bifurcation. What artifact is most likely responsible?
- Aliasing
- Mirror image artifact
- Intrinsic spectral broadening from a wide Doppler beam width at that depth (Correct answer)
- Range ambiguity
Correct answer: Intrinsic spectral broadening from a wide Doppler beam width at that depth
Intrinsic spectral broadening occurs because the Doppler beam has finite width; near a bifurcation the beam may intercept multiple vessels or disturbed flow regions, artificially broadening and elevating the displayed spectrum.
Question 3: In pulsed-wave Doppler, increasing the depth of the sample gate will require the system to:
- Increase PRF to maintain sensitivity
- Decrease PRF to allow sufficient time for echoes to return from the greater depth (Correct answer)
- Increase transmit frequency
- Decrease wall filter settings
Correct answer: Decrease PRF to allow sufficient time for echoes to return from the greater depth
Greater sample gate depth requires a longer round-trip travel time for the pulse echo, so PRF must be decreased to avoid range ambiguity.
Question 4: Which index is calculated as (PSV − EDV) / PSV and is used to describe the shape of an arterial Doppler waveform?
- Pourcelot (Resistivity) Index (Correct answer)
- Pulsatility Index
- S/D ratio
- Acceleration Index
Correct answer: Pourcelot (Resistivity) Index
The Resistivity Index (RI), also called the Pourcelot Index, is (PSV − EDV) / PSV and reflects downstream vascular resistance; values range from 0 (no resistance) to 1 (absent diastolic flow).
Question 5: A sample volume placed just distal to a significant arterial stenosis would be expected to show which spectral Doppler finding?
- A high-resistance triphasic waveform with sharp systolic upstroke
- A turbulent, broadened waveform with elevated peak velocity and possible aliasing (Correct answer)
- A normal monophasic low-resistance pattern
- Absent systolic peak with preserved diastolic flow
Correct answer: A turbulent, broadened waveform with elevated peak velocity and possible aliasing
Immediately distal to a stenosis, the high-velocity jet and turbulent post-stenotic flow cause spectral broadening, elevated velocities, and often aliasing on the PW Doppler tracing.
Question 6: The pulsatility index (PI) is calculated as (PSV − EDV) / mean velocity. Compared to the RI, the PI is preferred in which situation?
- When end-diastolic velocity is absent or reversed, making RI calculation impossible (Correct answer)
- When PSV exceeds 200 cm/s
- When the Doppler angle is greater than 60°
- When evaluating venous flow
Correct answer: When end-diastolic velocity is absent or reversed, making RI calculation impossible
When end-diastolic flow is absent or reversed (EDV = 0 or negative), the RI formula produces 1.0 or undefined values, but the PI can still differentiate degrees of high resistance using the time-averaged mean velocity.
Question 7: Which of the following best defines 'insonation angle' in Doppler ultrasound?
- The angle between two transducer crystals in a CW probe
- The angle between the ultrasound beam axis and the direction of blood flow (Correct answer)
- The angle of the sample volume gate relative to the vessel wall
- The angle of the spectral display baseline
Correct answer: The angle between the ultrasound beam axis and the direction of blood flow
The insonation angle (also called the Doppler angle or angle of incidence) is the angle between the ultrasound beam and the direction of blood flow, which must be known for accurate velocity calculation.
ARDMS SPI Pulsed-Wave and CW Doppler 4
What is the primary purpose of the fast Fourier transform (FFT) in spectral Doppler ultrasound?