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Vascular > Doppler > Flashcards

Doppler Flashcards

1
Q

Who first described the Doppler shirt/effect?

A

Christian Johann Doppler (1803-1853) an Austrian physicist

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2
Q

What is the Doppler effect?

A

A change in frequency of sound, light or waves caused by motion of the source or observer

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3
Q

What is the Doppler shift in ultrasound?

A

Change in frequency of sound caused by motion of RBC

Difference b/w transmitted freq and received freq

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4
Q

What happens to the frequency if the RBC are moving towards the transducer?

A

Echo freq will be larger then the transducer therefore antegrade flow

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5
Q

What happens to the frequency if the RBC are away from the transducer?

A

The echo frequency will be smaller therefore retrograde flow

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6
Q

What is the shift dependant on? (3)

A
  1. Transmitted freq
  2. Velocity of moving blood
  3. Angle b/w moving blood and the sound beam
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7
Q

What are the methods to detect and analyze Doppler shifts? (3)

A

Color flow
Spectral waveforms
Audible sounds

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8
Q

What is the most important factor that influences the calculation of the Doppler shift?

A

Angle of insonation

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9
Q

What angle would cause an ideal orientation for allowing the largest Doppler shift? What’s the COS?

A

Angle of 0

Cos0=1

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10
Q

What occurs when the blood flow when the angle is at 90deg?

A

There is no flow/shift detected because there is no measurable frequency

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11
Q

What is the angle of the transducer to the body to create blood flow?

A

30-60 deg to the blood vessel

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12
Q

Why do we want an insonation angle of 60deg?

A

Reduces the margin of error and is reproducible

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13
Q

What occurs when the Doppler angle is greater then 60deg?

A

Difficult to quantify because the errors in estimating the Doppler angle relative to the reflector velocity and spectral broadening which lead to errors in estimates of peak frequencies

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14
Q

How does the angle of insonation affect venous flow? (3)

A
  1. Angle is not important
  2. Velocities are not used
  3. Angle correct is set to zero
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15
Q

Examples of how the angles of insonation affects velocities

A

60deg - vel 124cm/s
34 deg - vel 68cm/s
79deg - vel 286cm/s

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16
Q

What is the simplest Doppler device?

A

CW Doppler

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17
Q

What happens to the returning signals of CW Doppler?

A

Returning signals are amplified and filtered therefore only allowing US frequencies or higher

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18
Q

Is there an image produced with CW Doppler?

A

No

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19
Q

Is it possible to set a depth and region to sample with CW Doppler? Why?

A

No because of the continuous nature of the transmitting frequency

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20
Q

What is an advantage of CW?

A

It can measure high velocities so there is no aliasing!

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21
Q

What is pulsed Doppler?

A

Sound pulses produced by the transducer at regular intervals

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22
Q

Can the operator adjust the controls to isolate signals from a desired depth in pulsed Doppler? Why?

A

Yes because the pulses are sent at set intervals

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23
Q

Can pulsed Doppler accurately receives signals from all depths?

A

No it is limited to certain depths

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24
Q

What factor limits the accurate measurement of high velocities by producing aliasing?

A

PRF

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25
Q

When does aliasing occur?

A

When the Doppler shift exceeds 1/2 PRF

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26
Q

What is the name of the limit that determines if aliasing occurs?

A

Nyquist limit

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27
Q

What is the Nyquist limit?

A

When the Doppler shift exceeds 1/2 PRF

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28
Q

Why does aliasing occur?

A

Insufficient time to collect signal information before the next pulse is sent out

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29
Q

What is Duplex Doppler?

A

The combination of Doppler instruments and realtime B mode

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30
Q

What is Fast Fourier transform?

A

The separation of the received Doppler shifts into individual frequency components and then displayed on a monitor

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31
Q

What does quadrate detection do?

A

Processes the signal as a + or - valve depending on direction of flow relative to the Doppler beam

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32
Q

What is pulsatility?

A

Relationship of the peak to min velocities over the mean velocity of an entire cycle

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33
Q

What are the types of pulsatility waveforms?

A

Low, moderate or high pul. Waveforms

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34
Q

What is resistivity?

A

Relationship of peak systolic velocity to end diastolic velocity

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35
Q

What type of resistance waveforms are there?

A

Low or high

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36
Q

Describe low resistance waveforms

A

Diastolic flow above zero

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37
Q

Describe high resistance waveforms

A

Shows reversed flow in early diastole

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38
Q

What type of waveform that provides a constant flow of blood? What organs need this?

A

Low resistance waveforms

Brain, kidneys, liver, spleen

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39
Q

What type of assessment does resistivity provide?

A

Qualitative and Quantitative

40
Q

What is the most common type of flow pattern?

A

Laminar flow

41
Q

Describe the laminar flow pattern

A
  • all particles moves forward in concentric rings

- highest velocity in the centre and gradually decreases as they approach the wall

42
Q

What is the average velocity of laminar parabolic flow equal to?

A

1/2 the maximum velocity

43
Q

What profiles describe parabolic flow?

A

Plug and Blunt

44
Q

What are factors affecting parabolic flow? (3)

A
  • Velocity
  • Changes in diameter of vessel
  • Curves, bifurcations and branch origins
45
Q

Describe disturbed pattern

A
  • Friction and energy looses start to disrupt laminar flow
  • Still forward flow but in diverging directions
  • Mild version of turbulence
46
Q

Is disturbed flow considered normal?

A

Yes

47
Q

Describe turbulent flow

A
  • non-linear flow
  • multiple directions (back and forth)
  • multiple velocity of blood particles
48
Q

Is turbulent flow considered normal?

A

No

49
Q

What does the adjutant of gain allow for?

A

Allow visualization without unwanted signal

50
Q

What does to high of gain cause?

A

False spectral broadening

Background noise or mirror image

51
Q

What does baseline do?

A

Adjusts to allow entire spectral signal to be seen

52
Q

What happens when the baseline is to high?

A

Aliasing

53
Q

What does a wall filter do?

A

Eliminates low frequency noise

54
Q

How should the wall filter be adjusted to optimize image?

A

Adjust so that low velocities are not missed on arterial or venous flow states

55
Q

How should scale, PRF and velocity range be adjusted?

A

Adjusted so all peak and min velocities are seen

56
Q

What are the 2 main methods to display Color?

A
  1. Standard method color

2. Power Doppler

57
Q

What is power Doppler?

A

Power or intensity of the signal so measured rather then Doppler shift

58
Q

What is power Doppler based on?

A

Density of RBCs not speed

59
Q

Does aliasing occur with spectral Doppler?

A

No

60
Q

Is power Doppler more or less sensitive of the Doppler angle?

A

More sensitive and independent

61
Q

What is power Doppler used to access?

A

Small vessels
Tissue perforation
Slow flow

62
Q

Why is power Doppler the preferred method when contrast is used?

A

Less subject to blooming

63
Q

Why is power Doppler not suitable when motion of tissue or pt is unavoidable?

A

Because it has a very slow FR

64
Q

Can flow direction be detected with power Doppler?

A

Not usually - power directional Doppler must be used to determine direction of flow

65
Q

What is color Doppler?

A

Stationary reflectors make up the gray scale portion of the image
Moving reflectors generate a Doppler shift and are shown within boundaries of color box

66
Q

What creates the Doppler shift in color Doppler?

A

Interference with moving RBCs

67
Q

What does color Doppler represent?

A

Mean frequency shift

68
Q

What is the significance of color coding in color Doppler?

A

Corresponds to the direction and velocity

69
Q

How does color Doppler create a real time image of frequency shifts related to movement?

A

Uses hundreds of scan sites along multiple scan lines

70
Q

What is autocorrelation?

A

Uses 6-20 pulses per scan line to provide info about received echos

71
Q

What information does a returning echo provide?

A
  • direction
  • average frequency shift
  • power or amplitude
  • variance
72
Q

Is color Doppler qualitative or quantitative?

A

Qualitative

73
Q

Why does color mode degrade the B mode image?

A

Because color mode reduces the PRF

74
Q

When adding color flow to imaging, what happens to the frame rate?

A

FR decreases

75
Q

Does the height affect the FR?

A

No

76
Q

What happens to the FR when the box is narrowed?

A

FR increases

77
Q

What is the color flow derived from?

A

Weak echos from RBCs

78
Q

What type of bar or wheel color maps are available?

A

Shifting hue
Changing shade
Variance maps

79
Q

What is the most common color map?

A

Shifting hue

80
Q

What is another name for changing shade?

A

Saturation

81
Q

Which color map has the ability to “tag” certain frequencies?

A

Variance maps

82
Q

How do you optimize velocity range?

A

High flow/ high PRF

Low flow/ low PRF

83
Q

How does the FOV (depth) affect color optimization?

A

Greater depth to an area of interest degrades the image and ability to display flow

84
Q

What happens when the Color scale (PRF) is to low?

A

Aliasing

85
Q

What happens to the image when the Color scale (PRF)to to high?

A

Flow not being detected and/or poor color fill in

86
Q

What is the most underused control?

A

Gain

87
Q

What results when insufficient gain is used?

A

Poor color fill in

88
Q

How do you properly adjust for gain?

A

Increased to a point of blooming/bleeding artifact then back to the thereshold

89
Q

What’s the threshold for gain?

A

Gain level just before blooming occurs

90
Q

What is color priority?

A

Image processing priority- color vs grey scale

91
Q

What happens when the wall filter is set to high?

A

Eliminate low flow information (near baseline)

92
Q

Why should the baseline be adjusted to the middle of scale?

A

To accommodate more red or blue velocities (not usually done)

93
Q

When is power/angio used?

A

In cases of trickle flow or low flow states

94
Q

What is mirror image artifact?

A

Reflection of the image produced below
Seen in grey scale, color and spectral
See pg. 17

95
Q

What can occur if your color gain is set to high?

A

May obscure pathology

96
Q

When would color flash occur?

A

When transmitted pulses or adjacent motion will cause color to flash outside the vessel (heart motion)

97
Q

What is visible bruit?

A

Soft tissue vibration adjacent to area of high flow

Vascular (5 decks)

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