ARDMS SPI Color Doppler and Artifacts 4 — Questions and Answers
Question 1: The Nyquist limit for color Doppler is defined as:
- The maximum detectable depth
- Half the pulse repetition frequency (Correct answer)
- The minimum detectable velocity
- The maximum ensemble length
Correct answer: Half the pulse repetition frequency
The Nyquist limit equals PRF/2; velocities producing Doppler shifts above this threshold will alias and wrap to the opposite color.
Question 2: Color priority threshold in color Doppler determines:
- Which pixels display color versus grayscale based on echo amplitude (Correct answer)
- The maximum velocity displayed
- How many pulses form one color line
- The color hue assigned to arterial flow
Correct answer: Which pixels display color versus grayscale based on echo amplitude
Color priority sets the brightness level above which grayscale tissue signal overrides color, preventing color from painting solid structures.
Question 3: Spectral broadening on a color Doppler-guided pulsed wave trace at a stenosis is caused by:
- Aliasing of the color signal only
- A wide range of velocities from turbulent flow filling the spectral window (Correct answer)
- Incorrect insonation angle
- An overly narrow sample volume
Correct answer: A wide range of velocities from turbulent flow filling the spectral window
Turbulent flow post-stenosis contains a broad distribution of velocities that fill the spectral window, producing spectral broadening.
Question 4: Which artifact can make a non-vascular structure such as a simple cyst appear to contain color Doppler signal?
- Twinkling artifact
- Color bleed (blooming) (Correct answer)
- Acoustic shadowing
- Bayesian noise
Correct answer: Color bleed (blooming)
Excessive color gain (blooming) can cause color signal to spill into adjacent avascular structures such as simple cysts.
Question 5: In color Doppler, increasing the color box angle (steering) away from perpendicular to the vessel:
- Reduces the detectable velocity range
- Improves Doppler angle and increases color sensitivity (Correct answer)
- Increases the PRF automatically
- Eliminates aliasing
Correct answer: Improves Doppler angle and increases color sensitivity
Steering the color box to achieve a smaller insonation angle increases the cosine factor, producing larger frequency shifts and better color filling.
Question 6: A patient's renal artery color Doppler shows a focal zone of aliasing followed by a color void. What does the color void most likely represent?
- Laminar flow at low velocity
- Complete occlusion distal to the stenosis
- An area of post-stenotic turbulence causing signal cancellation (Correct answer)
- Acoustic shadowing from calcification
Correct answer: An area of post-stenotic turbulence causing signal cancellation
Severe turbulence can cause destructive interference of returning signals, creating apparent color voids distal to a tight stenosis.
Question 7: The color Doppler 'ghosting' artifact differs from flash artifact in that ghosting:
- Is caused by high gain rather than motion
- Appears as persistent color in a specific location after the source has moved (Correct answer)
- Fills the entire color box
- Only occurs with power Doppler
Correct answer: Appears as persistent color in a specific location after the source has moved
Ghosting is a residual color signal that lingers at a location after a moving structure has passed, due to slow color frame updates.
ARDMS SPI Color Doppler and Artifacts 4
The Nyquist limit for color Doppler is defined as: