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Physics > Color Doppler > Flashcards

Color Doppler Flashcards

1
Q

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

A

Mean flow velocity

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2
Q

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

A

Multiple sample gates

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3
Q

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

A

Longer transmit pulse time

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4
Q

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

A

“Color Packets” or “Color Ensemble”

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5
Q

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

A

Multiple

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6
Q

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

A

Number of pulses

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7
Q

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

A

More accurate

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8
Q

Too small a packet size leads to ______ flow measurements

A

Inaccurate

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9
Q

What results from a packet having more pulses?

A
  • 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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10
Q

Which Doppler has the worst temporal resolution?

A

Color Doppler

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11
Q

Does Color Doppler have the best or worst temporal resolution

A

Worst temporal resolution

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12
Q

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

A

Temporal resolution

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13
Q

Autocorrelation (time correlated) is…

A

digital technique used to analyze color flow Doppler

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14
Q

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

A

Autocorrelation (time correlated)

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15
Q

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

A

mean frequency, amplitude, and variance or turbulence

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16
Q

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

A

Top
Bottom

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17
Q

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

A

The baseline and the color wall filters

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18
Q

An absence of color in the image is detected when?

A

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

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19
Q

What are the 2 kinds of color maps?

A

Velocity Maps
Variance Maps

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20
Q

Nyquist limit

A

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

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21
Q

What is measured by velocity mode

A

A mean velocity

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22
Q

Nyquist set too low a scale will cause?

A

Aliasing

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23
Q

Nyquist set too high will result in

A

lack of color filling in the vessel

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24
Q

PRF should be set at approximately _________

A

1/2 of the expected velocity

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25
Q

Poor blood flow visualization will (decrease/increase) distance to the target

A

Increase
(The color box is positioned too deep)

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26
Q

If the colors that touch each other in the image go through the map’s middle, this equals

A

Flow reversal (turbulence)

27
Q

If the colors that touch each other go around the outside of the map, then _______ is present

A

Aliasing

28
Q

What display seperates the primary colors (red, blue) with the baseline color (black) and mixture of other colors

A

turbulent

29
Q

______ will seperate the primary colors with other colors depending on the color map but never with black

A

aliasing

30
Q

What do variance maps display

A

different colors side to side

31
Q

Colors on the left side of the variance map indicate

A

laminar flow

32
Q

colors on the right side of the variance map

A

indicate turbulent flow

33
Q

What are the typical colors of variability

A

yellow and green

34
Q

Variance mode distinguishes ___ flow from ___ flow

A

laminar from turbulent

35
Q

How much flow is depicted when the flow is at a 90° angle to the transducer

A

No flow is depicted

36
Q

Color dropout exists not because there is an absence of flow but because the insonification is close to _____

A

90° (perpendicular)

37
Q

Optimal Doppler angle

A

parallel to the vector of blood flow

38
Q

Hue

A

determind by its wavelength

39
Q

Saturation

A

How much white is added compared to the original color

A color can appear lighter by adding white to it

40
Q

Brightness

A

how intense the color is and related to the amplitude of the signal

41
Q

Wall filters eliminate

A

color aliasing from slow velocity reflectors

42
Q

in essence wall filters serve as a “____” for Doppler

A

reject

43
Q

Color gain is

A

amplification applied to the color Doppler component of the image during processing

44
Q

Color gain amplifies

A

the signal after it has been received back from the patient

45
Q

What is color persistence?
(aka called temporal averaging/temporal compounding)

A

temporal smoothing technique to reduce noise

46
Q

What is the goal of color persistence
(aka temporal averaging/temporal compounding)

A

to “average” frames over time to improve the signal to noise ratio

47
Q

Color persistence positives:

A
  • Smoother image w/reduced noise
  • Higher signal to noise ratio
  • Improves image quality
48
Q

Color persistence limitations:

A
  • Reduces FR
  • Reduce temporal resolution
  • Most effective with slow moving structures
49
Q

Low Color Priority (threshold)

A

allows valid grey scale information to override Doppler information

50
Q

High Color Priority

A

allows color Doppler information to override grey scale information

51
Q

Lowering the threshold displays

A

more greyscale and less color

52
Q

low color priority results in

A

poor filling of the vessel lumen

53
Q

Power Doppler displays the _____ of the Doppler signal

A

Amplitude

54
Q

Power Doppler is approximately ___ times more sensitive than color and eliminates many color artifacts

A

3

55
Q

Power mode is ______ color Doppler

A

non-directional

56
Q

The power map emphasizes

A

the quantity of blood flow

57
Q

Power Doppler is used when

A

extreme sensitivity to low/slow flow is needed

58
Q

Power Doppler is ____ to Color Doppler in outlining vessel walls and depicting residual lumens in high grade stenotic lesions (superior/inferior)

A

Superior

59
Q

Power Doppler has no ____ since it is measuring the amount of flow and not frequency change

A

aliasing

60
Q

3 advantages of Power Doppler:

A
  1. Extreme sensitivity to low/slow flow states
  2. Unaffected by Doppler angles
  3. No aliasing
61
Q

5 disadvantages of Power Doppler:

A
  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
62
Q

The term blossoming is used to refer to a signal that

A

is over-gained so the signal bleeds into neighboring regions of the spectrum

63
Q

Twinkling artifact appearance:

A

region appears as rapidly changing mix of colors

64
Q

Twinkling artifact causes:

A

the presence of small strongly reflective objects within the Doppler study

Physics (2 decks)

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