Color Doppler Flashcards by Angela Mel

Color Doppler uses the Doppler effect and then correlates the frequency shift recorded to estimate the

Mean flow velocity

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Color Doppler obtains it’s information from how many sample gates

Multiple sample gates

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For color imaging is the transmit pulse time longer or shorter than used in B-mode

Longer transmit pulse time

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To register a mean Doppler shift color must transmit multiple acoustic lines, these multiple lines are referred to as

“Color Packets” or “Color Ensemble”

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For Color Doppler each line of site must be pulsed ______ times (pulse/listen cycles)

Multiple

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The accuracy of Doppler velocity measurements depends upon the ________ in the packet (the packet size)

Number of pulses

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The more pulses in the packet, the ______ the velocity measurement

More accurate

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Too small a packet size leads to ______ flow measurements

Inaccurate

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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

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Which Doppler has the worst temporal resolution?

Color Doppler

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Does Color Doppler have the best or worst temporal resolution

Worst temporal resolution

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Choosing a large packet produces smoother color with less noise but will sacrifice what?

Temporal resolution

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Autocorrelation (time correlated) is…

digital technique used to analyze color flow Doppler

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What is the digital technique used to analyze color flow Doppler?

Autocorrelation (time correlated)

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Autocorrelation correlates the data from the multiple sample sites and analyzes it for…

mean frequency, amplitude, and variance or turbulence

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The plus is assumed to be on the ___ and the minus on the ____

Top
Bottom

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What does the black band in the center of the color bar represent?

The baseline and the color wall filters

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An absence of color in the image is detected when?

No frequency shift (90•) or a low frequency is detected

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What are the 2 kinds of color maps?

Velocity Maps
Variance Maps

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Nyquist limit

Highest Doppler frequency or velocity that can be measured without the appearance of aliasing

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What is measured by velocity mode

A mean velocity

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Nyquist set too low a scale will cause?

Aliasing

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Nyquist set too high will result in

lack of color filling in the vessel

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PRF should be set at approximately _________

1/2 of the expected velocity

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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 ## Footnote 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

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:

1. Extreme sensitivity to low/slow flow states 2. Unaffected by Doppler angles 3. No aliasing

5 disadvantages of Power Doppler:

1. No measurement of velocity or direction 2. Lower FR's than Color Doppler 3. Susceptible to motion of the transducer, patient, or soft tissues, which may result in a burst of color or flash artifacts 4. More sensitive to motion than color 5. 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