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Physics > Doppler > Flashcards

Doppler Flashcards

1
Q

What is the Doppler principle?

A

The physical principle used to measure the velocity of blood in circulation

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2
Q

Define demodulation in the context of Doppler.

A

The process of extracting the low Doppler frequency from the transducer’s carrier frequency

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3
Q

What are positive Doppler shifts?

A

When blood cells move toward the transducer, causing the reflected frequency to be higher than the transmitted frequency

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4
Q

What are negative Doppler shifts?

A

When blood cells move away from the transducer, causing the reflected frequency to be lower than the transmitted frequency

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5
Q

What does the Doppler shift represent?

A

The difference between the reflected frequency and the transmitted frequency

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6
Q

Fill in the blank: Doppler shift (Hz) = _______.

A

reflected freq. - transmitted freq.

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7
Q

What is measured velocity in Doppler?

A

Defined by a magnitude and a direction

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8
Q

What is the formula for Doppler shift?

A

Doppler shift = 2 x velocity of blood x transducer freq. x cosine

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9
Q

What does the cosine factor represent in the Doppler shift formula?

A

The angle between sound and vessels

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10
Q

What does bidirectional Doppler distinguish?

A

The direction of flow toward or away from the transducer

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11
Q

What does a spectral tracing below the baseline indicate?

A

A negative shift or flow away from the transducer

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12
Q

What does a spectral tracing above the baseline indicate?

A

A positive shift or flow toward the transducer

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13
Q

What is Continuous Wave (CW) Doppler?

A

A commonly used signal processing technique for bidirectional Doppler

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14
Q

What are the advantages of CW Doppler? List at least two.

A
  • Ability to accurately measure very high velocities
  • Very small Doppler shifts can be detected
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15
Q

What is a disadvantage of CW Doppler?

A

Cannot determine the exact location of moving blood cells due to range ambiguity

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16
Q

What does range ambiguity refer to?

A

The inability to determine depth of reflections due to overlap of transmit and receive beams

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17
Q

Fill in the blank: Simultaneous anatomic imaging and Doppler fusion is achieved with _______.

A

2D US + MRI/CT

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18
Q

What does duplex imaging/scanning refer to?

A

Velocities sampled every second in blood circulation

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19
Q

What are the two Doppler shifts in the Doppler shift formula?

A
  • Reception of sound wave by moving RBC
  • Transducer’s reception of the sound wave from the moving RBC
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20
Q

What is the significance of the number 2 in the Doppler shift equation?

A

Represents that there are actually 2 Doppler shifts involved

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21
Q

What does PW Doppler stand for?

A

Pulsed Wave Doppler

PW Doppler is a type of ultrasound that measures blood flow velocities.

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22
Q

What is range resolution in the context of PW Doppler?

A

The ability to select the exact location where velocities are measured

This is achieved by placing a small marker called the gate or sample volume on a 2D image.

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23
Q

What is aliasing in Doppler ultrasound?

A

Inaccurate measurement of high velocity signals

It can result in high velocity flow being displayed as traveling in the opposite direction.

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24
Q

What is the Nyquist limit?

A

The highest Doppler frequency or velocity that can be measured without aliasing

It is defined as Nyquist limit (Hz) = PRF / 2.

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25
Q

What does the color map do in Color Flow Doppler?

A

Converts measured velocities into colors on the image

It displays flow direction and velocity through a vertical bar of various colors.

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26
Q

What is the primary advantage of PW Doppler?

A

Ability to select the exact location for velocity measurement

This is facilitated by the use of a gate or sample volume.

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27
Q

Fill in the blank: The most common error associated with Doppler ultrasound is that high velocity flow in one direction is incorrectly displayed as traveling in the _______.

A

opposite direction

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28
Q

What are the two most common dictionaries used in Color Flow Doppler?

A
  • Velocity mode
  • Variance mode
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29
Q

True or False: Aliasing never occurs with Continuous Wave (CW) Doppler.

A

True

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30
Q

What is the relationship between the amplitude of the reflected signal and the number of blood cells?

A

Related to the number of blood cells creating the reflection

A higher number of blood cells leads to a stronger reflected signal.

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31
Q

What type of information does Color Flow Doppler provide?

A

Direction of flow and average or mean velocities

This is done through color-coded velocity information superimposed on a gray scale image.

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32
Q

What is the effect of scanning deeper regions in relation to Doppler sampling rate?

A

Aliasing can occur if the sampling rate is too low compared to measured blood velocities

This is particularly relevant when measuring high velocity flows.

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33
Q

What is the significance of the black bar in the Color Map?

A

Indicates ‘no Doppler shift’

It serves as a reference point for determining flow direction.

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34
Q

How does Color Flow Doppler differ from PW Doppler regarding the importance of angle knowledge?

A

Knowledge of angle is less important than in CW or PW Doppler

This allows for more flexibility in imaging techniques.

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35
Q

What is a characteristic of the Velocity mode in Color Flow Doppler?

A

Reports average or mean velocities

This mode provides a simplified representation of flow dynamics.

36
Q

Fill in the blank: Color Flow Doppler is considered _______.

A

semi-quantitative

37
Q

What is Variance Mode used for?

A

To distinguish laminar flow from turbulent flow

Variance Mode provides color change side-to-side as well as up and down.

38
Q

What are Doppler Packets?

A

Groups of multiple ultrasound pulses used to determine blood velocities

Larger packets or longer ensemble lengths result in more accurate velocity measurements.

39
Q

What is Power Doppler?

A

Non-directional color Doppler that detects flow without velocity or direction information

The amplitude of the reflection is directly related to the number of moving blood cells.

40
Q

What does Spectral Analysis involve?

A

Breaking complex signals into basic building blocks to identify velocities

It can be performed using methods like Fast Fourier Transform (FFT) and Autocorrelation.

41
Q

Fill in the blank: The digital technique used to process both PW and CW Doppler signals is _______.

A

[Fast Fourier Transform (FFT)]

42
Q

What is the purpose of the Spectral Window in Doppler analysis?

A

To indicate the range of velocities in a spectral trace

A clear spectral window suggests laminar flow, while spectral broadening indicates turbulent flow.

43
Q

What are the advantages of using Fast Fourier Transform (FFT)?

A
  • Exceedingly accurate
  • Displays all individual velocity components
  • Distinguishes laminar from turbulent flow
44
Q

What are the disadvantages of using larger Doppler packets?

A
  • More time needed to acquire data
  • Reduced frame rate
  • Decreased temporal resolution
  • Subject to aliasing
45
Q

True or False: Color change in Velocity Mode is always up and down.

A

True

46
Q

What is Autocorrelation?

A

A digital technique used to analyze color flow Doppler signals

It is substantially faster than FFT but less accurate.

47
Q

What does a filled spectral window indicate?

A

Turbulent flow

It represents a wider range of velocities and Doppler shifts within the sample volume.

48
Q

Fill in the blank: The packet size should be selected to balance accurate velocity measurements and adequate _______.

A

[temporal resolution]

49
Q

What is the primary concern with conventional color flow Doppler?

A

Prone to aliasing and lower frame rates

This reduces temporal resolution.

50
Q

What is the effect of slight motion of the transducer or patient on Power Doppler?

A

Prone to ‘lash artifact’

This can affect the accuracy of the flow detection.

51
Q

What is Doppler Shift measured in?

A

Hertz

52
Q

What factors are directly related to Doppler Shift?

A
  • Velocity
  • Transducer frequency
  • Cosine of the angle between flow direction and sound direction
53
Q

What is the effect of an angle of 30 degrees on aliasing?

A

Less aliasing

54
Q

What angle results in maximum aliasing?

A

180 degrees

55
Q

What factors affect aliasing?

A
  • Slower blood velocity
  • Lower frequency transducer
  • Shallow gate (high PRF)
56
Q

What is the first technique to eliminate aliasing?

A

Adjust the scale (PRF) to its maximum

57
Q

What is the second technique to eliminate aliasing?

A

New, shallower view (sample volume)

58
Q

What is the third technique to eliminate aliasing?

A

Lower transducer frequency

59
Q

What is the fourth technique to eliminate aliasing?

A

Use baseline shift (down/zero)

60
Q

What does range resolution affect?

A

The ability to distinguish between two closely spaced objects

61
Q

What is the maximum velocity limitation related to?

A

Nyquist limit

62
Q

What is the result of increasing the Nyquist limit?

A

Increases the ability to measure maximum velocity with Doppler

63
Q

What is the disadvantage of using a higher frequency transducer?

A

Less sensitive to very small Doppler shifts/low velocities

64
Q

What is a characteristic of Continuous Wave (CW) Doppler?

A

No aliasing

65
Q

What is a consequence of using a deep gate in Doppler?

A

Increases Nyquist limit

66
Q

Fill in the blank: Aliasing remains, but display is more ______.

A

appealing

67
Q

True or False: Aliasing is ineffective if the Doppler shift wraps around itself completely.

A

True

68
Q

What happens when the sample volume is shallower?

A

Less aliasing

69
Q

What is the effect of a lower frequency transducer on aliasing?

A

Reduces aliasing

70
Q

What is a key component of a Pulsed Doppler Transducer?

A

At least one crystal

The crystal is essential for converting electrical signals into ultrasound waves.

71
Q

What type of backing material is used in a Pulsed Doppler Transducer?

A

Dampened PZT

PZT stands for lead zirconate titanate, which is commonly used in ultrasound transducers.

72
Q

What is the Q-factor of a Pulsed Doppler Transducer?

A

Low Q-factor

A low Q-factor contributes to a wider bandwidth in the transducer’s operation.

73
Q

What is one advantage of using higher frequency in Doppler imaging?

A

Improves resolution

Higher frequency ultrasound waves provide better detail in imaging.

74
Q

What is the incidence angle for normal Doppler imaging?

A

90 degrees

Normal incidence is crucial for accurate Doppler measurements.

75
Q

What phenomenon is characterized by the appearance of a second vessel color flow below the anatomical region of interest?

A

Mirror image

This artifact occurs in color flow Doppler imaging due to reflection.

76
Q

What is the primary purpose of Color Flow Doppler?

A

Provides 2D flow information directly on anatomic image

This allows visualization of blood flow patterns in relation to structures.

77
Q

What type of Doppler modality is most sensitive?

A

Continuous Wave

Continuous Wave Doppler is designed to detect high-velocity blood flow without aliasing.

78
Q

What is a disadvantage of using Pulsed Wave Doppler?

A

Subject to aliasing

Aliasing occurs when the velocity exceeds the Nyquist limit.

79
Q

Fill in the blank: The __________ mode is used with low velocity or small volume blood flow.

A

Power Mode

Power Mode is particularly effective for detecting low-velocity flows.

80
Q

What is the effect of increasing the Wall Filter in Doppler imaging?

A

Rejects low-frequency Doppler signals

This helps to eliminate clutter and improve the quality of the Doppler signal.

81
Q

What is the minimum number of crystals required for a Continuous Wave Doppler Transducer?

A

At least 2 crystals

Continuous Wave requires two crystals for simultaneous transmission and reception.

82
Q

True or False: Pulsed Wave Doppler provides good range resolution.

A

True

Pulsed Wave Doppler is known for its ability to accurately identify the location of flow.

83
Q

What happens to the temporal resolution in Color Flow Doppler due to multiple packets?

A

Reduced temporal resolution

Using multiple packets can slow down the acquisition of frames, affecting temporal resolution.

84
Q

What is a common artifact seen in Color Flow Doppler imaging?

A

Clutter

Clutter can obscure true blood flow signals, making interpretation difficult.

85
Q

What does the term ‘range ambiguity’ refer to in Doppler modalities?

A

Ambiguity in determining the exact location of flow

This can occur in Continuous Wave Doppler due to its inability to provide depth information.

86
Q

What is the primary measurement outcome of Doppler modalities?

A

Peak velocity measurements

Doppler imaging primarily measures the maximum velocity of blood flow.

87
Q

Fill in the blank: The __________ spectrum appears both above and below the baseline in Pulsed Wave Doppler.

A

Mirror image

This occurs due to reflections and can complicate the interpretation of flow.

Physics (24 decks)

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