Color Doppler Flashcards
Color Doppler uses the Doppler effect and then correlates the frequency shift recorded to estimate the
Mean flow velocity
Color Doppler obtains it’s information from how many sample gates
Multiple sample gates
For color imaging is the transmit pulse time longer or shorter than used in B-mode
Longer transmit pulse time
To register a mean Doppler shift color must transmit multiple acoustic lines, these multiple lines are referred to as
“Color Packets” or “Color Ensemble”
For Color Doppler each line of site must be pulsed ______ times (pulse/listen cycles)
Multiple
The accuracy of Doppler velocity measurements depends upon the ________ in the packet (the packet size)
Number of pulses
The more pulses in the packet, the ______ the velocity measurement
More accurate
Too small a packet size leads to ______ flow measurements
Inaccurate
What results from a packet having more pulses?
- Velocity measurement more accurate
- More time is required to collect data from each scan line
- More pulses are needed to make a single frame
- Frame rate is lower
- Temporal resolution is reduced
Which Doppler has the worst temporal resolution?
Color Doppler
Does Color Doppler have the best or worst temporal resolution
Worst temporal resolution
Choosing a large packet produces smoother color with less noise but will sacrifice what?
Temporal resolution
Autocorrelation (time correlated) is…
digital technique used to analyze color flow Doppler
What is the digital technique used to analyze color flow Doppler?
Autocorrelation (time correlated)
Autocorrelation correlates the data from the multiple sample sites and analyzes it for…
mean frequency, amplitude, and variance or turbulence
The plus is assumed to be on the ___ and the minus on the ____
Top
Bottom
What does the black band in the center of the color bar represent?
The baseline and the color wall filters
An absence of color in the image is detected when?
No frequency shift (90•) or a low frequency is detected
What are the 2 kinds of color maps?
Velocity Maps
Variance Maps
Nyquist limit
Highest Doppler frequency or velocity that can be measured without the appearance of aliasing
What is measured by velocity mode
A mean velocity
Nyquist set too low a scale will cause?
Aliasing
Nyquist set too high will result in
lack of color filling in the vessel
PRF should be set at approximately _________
1/2 of the expected velocity
Poor blood flow visualization will (decrease/increase) distance to the target
Increase
(The color box is positioned too deep)
If the colors that touch each other in the image go through the map’s middle, this equals
Flow reversal (turbulence)
If the colors that touch each other go around the outside of the map, then _______ is present
Aliasing
What display seperates the primary colors (red, blue) with the baseline color (black) and mixture of other colors
turbulent
______ will seperate the primary colors with other colors depending on the color map but never with black
aliasing
What do variance maps display
different colors side to side
Colors on the left side of the variance map indicate
laminar flow
colors on the right side of the variance map
indicate turbulent flow
What are the typical colors of variability
yellow and green
Variance mode distinguishes ___ flow from ___ flow
laminar from turbulent
How much flow is depicted when the flow is at a 90° angle to the transducer
No flow is depicted
Color dropout exists not because there is an absence of flow but because the insonification is close to _____
90° (perpendicular)
Optimal Doppler angle
parallel to the vector of blood flow
Hue
determind by its wavelength
Saturation
How much white is added compared to the original color
A color can appear lighter by adding white to it
Brightness
how intense the color is and related to the amplitude of the signal
Wall filters eliminate
color aliasing from slow velocity reflectors
in essence wall filters serve as a “____” for Doppler
reject
Color gain is
amplification applied to the color Doppler component of the image during processing
Color gain amplifies
the signal after it has been received back from the patient
What is color persistence?
(aka called temporal averaging/temporal compounding)
temporal smoothing technique to reduce noise
What is the goal of color persistence
(aka temporal averaging/temporal compounding)
to “average” frames over time to improve the signal to noise ratio
Color persistence positives:
- Smoother image w/reduced noise
- Higher signal to noise ratio
- Improves image quality
Color persistence limitations:
- Reduces FR
- Reduce temporal resolution
- Most effective with slow moving structures
Low Color Priority (threshold)
allows valid grey scale information to override Doppler information
High Color Priority
allows color Doppler information to override grey scale information
Lowering the threshold displays
more greyscale and less color
low color priority results in
poor filling of the vessel lumen
Power Doppler displays the _____ of the Doppler signal
Amplitude
Power Doppler is approximately ___ times more sensitive than color and eliminates many color artifacts
3
Power mode is ______ color Doppler
non-directional
The power map emphasizes
the quantity of blood flow
Power Doppler is used when
extreme sensitivity to low/slow flow is needed
Power Doppler is ____ to Color Doppler in outlining vessel walls and depicting residual lumens in high grade stenotic lesions (superior/inferior)
Superior
Power Doppler has no ____ since it is measuring the amount of flow and not frequency change
aliasing
3 advantages of Power Doppler:
- Extreme sensitivity to low/slow flow states
- Unaffected by Doppler angles
- No aliasing
5 disadvantages of Power Doppler:
- No measurement of velocity or direction
- Lower FR’s than Color Doppler
- Susceptible to motion of the transducer, patient, or soft tissues, which may result in a burst of color or flash artifacts
- More sensitive to motion than color
- Can provide false data on the existence of blood when used at extremely low PRF/scale settings
The term blossoming is used to refer to a signal that
is over-gained so the signal bleeds into neighboring regions of the spectrum
Twinkling artifact appearance:
region appears as rapidly changing mix of colors
Twinkling artifact causes:
the presence of small strongly reflective objects within the Doppler study
