# Ch 19: Doppler Flashcards

1
Q

Relative motion between the sound source and the receiver creates…

A

a frequency change.

2
Q

The frequency of sound changes when the sound source and the receiver move…

A

closer together or farther apart.

3
Q

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

A

demodulation.

4
Q

When the Doppler shift is positive, blood cells are traveling __ the transducer.

A

towards

5
Q

Doppler shifts range from __ and are in the range of audible sound.

A

20 Hz to 20,000 Hz

6
Q

reflected frequency - transmitted frequency =

A

Doppler shift (Hz)

7
Q

When blood cells move away from the transducer, the Doppler shift is…

A

negative.

8
Q

When the Doppler shift is negative, the reflected frequency is __ than the transmitted frequency.

A

lower

9
Q

T/F? Speed is magnitude and direction.

A

FALSE, just magitude

10
Q

This indicates the distance that a red blood cell moves in one second.

A

speed

11
Q

Speed is reported in units of…

A

distance divided by time (cm/s).

12
Q

This is defined by magnitude and direction.

A

velocity

13
Q

Doppler shift is __ related to the velocity of the RBCs.

A

directly. The faster the veloctiy, the greated the Doppler frequency.

14
Q

How many Doppler shifts are there during an ultrasound exam?

A

two

15
Q

How do ultrasound systems report blood velocity?

A

in cm/s, not Hz

16
Q

The Doppler shift is __ related to the frequency of the transmitted sound.

A

directly. If the frequency is doubled, the shift will also be doubled.

17
Q

When the blood cells are moving __ to the sound beam, the entire velocity is measured.

A

parallel

18
Q

When an angle exists between the direction of the flow and the sound beam, the measured velocity is…

A

less than the true velocity.

19
Q

The percentage of the velocity that is measured depends on the __ between the sound beam and the direction of motion.

A

cosine of the angle

20
Q

The Doppler shift is __ related to the consine of the angled between the direction of flow and the sound.

A

directly. If the cosine is reduced by half, the measured shift will be halved.

21
Q

What is the relationship between the true velocity and the measured velocity when blood moves parallel to the beam?

A

They are equal.

22
Q

What is the relationship between true and measured velocities when blood moves perpendicular to the sound beam/

A

Trick question! Cannot be measured.

23
Q

What is the relationship between true and measured velocities when blood moves at a 60 degree angle to the beam?

A

Measured will be one half the true velocity.

24
Q

This is a commonly used signal processing technique for bidirectional Doppler.

A

25
Q

What is the advantage of continuous wave Doppler?

A

Its ability to accurately measure very high velocities.

26
Q

What is the primary disadvantage of continuous wave Doppler?

A

The exact location of the moving blood cells cannot be determined.

27
Q

The limitation of continuous wave Doppler wherein signals arise from all blood cells in the region of of the beam is called…

A

range ambiguity.

28
Q

What is the secondary disadvantage of continuous wave Doppler?

A

Its lack of time gain compensation.

29
Q

Doppler shifts produced by continuous wave from deeper blood cells may be incorrectly interpreted as having been created by __ blood cells.

A

fewer

30
Q

Dedicated continuous wave transducers are made with how many elements?

A

two

31
Q

Simultaneous anatomic imaging and Doppler is called…

A

duplex imaging.

32
Q

Dedicated continuous wave transducers do not use backing material which results in the following…

A
1. undampened tranmitted signal
2. narrow bandwidth
3. high quality factor
4. high sensitivity
33
Q

Dedicated continuous wave transducers have increased…

A

sensitivity.

34
Q

T/F? Dedicated continuous wave transducers do not have a matching layer.

A

FALSE, yes they do.

35
Q

How many crystals are necessary in pulsed wave Doppler?

A

one

36
Q

What is the greatest advantage of pulse Doppler?

A

Being able to select the exact location where velocities are measured.

37
Q

This is the ability to select the exact location where velocities are to be measured.

A

range resolution, range specificity, freedom from range ambiguity artifact

38
Q

What is the primary disadvantage of pulsed Doppler?

A

Inaccurate measurement of high velocity signals.

39
Q

This is when high velocity flow in one direction is incorrectly displayed as traveling in the opposite direction.

A

aliasing

40
Q

Studies that simultaneously perform imaging and pulsed Doppler are called..

A

duplex examinations.

41
Q

T/F? Pulsed Doppler transducers contain backing material.

A

true

42
Q

This is the very top and bottom of the spectral display.

A

Nyquist limit

43
Q

What conditions create aliasing?

A
1. pulsed (not continuous wave) Doppler

2. the samping rate being to low

44
Q

The Nyquist limit is __ of the pulse repetition frequency.

A

one half

45
Q

Two ways to avoid aliasing are…

A
1. raise the Nyquist limit

2. reduce the Doppler shift

46
Q

When the sample volume is deep, the PRF is __ and the Nyquist limit is __.

A

low, low

47
Q

Because the velocity is sampled fewer times at deeper volumes, the system is unable to…

A

accurate measure high velocities and creates aliasing.

48
Q

When the sample volume is shallow, the PRF is __ and the Nyquist limit is __.

A

high, high

49
Q

Because the velocity is sampled more times at shallower volumes, the system is able to…

A

meaure high velocities without aliasing.

50
Q

How does transducer frequency affect aliasing?

A

The higher the frequency, the more aliasing created.

51
Q

T/F? Aliasing artifacts are less common with higher frequency transducers.

A

FALSE, lower

52
Q

Five techniques to avoid aliasing…

A
1. adjust the scale to its max
2. select a new view with a shallower sample volume
3. select a lower frequency transducer
4. use baseline shift
5. use continuous wave Doppler
53
Q

When the PRF is increased, the Nyquist limit is…

A

increased, too.

54
Q

What is the disadvantage to maximizing the scale to avoid aliasing?

A

Loss of sensitivity to low velocities. Aliasing may persist anyway.

55
Q

When a shallower sample volume is selected, the PRF is…

A

increased.

56
Q

What is the disadvantage to selecting a shallower sample volume?

A

none

57
Q

Why does a lower frequency transducer reduce aliasing?

A

Because lower frequencies create lower Doppler shifts that are more likely to be less than the Nyquist limit.

58
Q

What is the disadvantage of selecting a lower frequency transducer to reduce aliasing?

A

The anatomic image may be of lower quality.

59
Q

What is the advantage of shifting the baseline to avoid aliasing?

A

High velocity flows are displayed in the proper direction.

60
Q

What is the disadvantage of shifting the baseline to avoid aliasing?

A

The sound still comes from the wrong speaker. The shift may be so high that it doesn’t help.

61
Q

T/F? Aliasing never appears with continuous wave Doppler.

A

true

62
Q

What is the disadvantage of using continuous wave Doppler to avoid aliasing?

A

Range ambiguity

63
Q

Gray shades on a Doppler spectrum are related to…

A
1. amplitude of the reflected signal

2. number of blood cells creating the reflection

64
Q

This is a form of two dimensional Doppler.

A

color flow

65
Q

T/F? Color Doppler is a continuous wave technique.

A

FALSE, pulsed

66
Q

T/F? Color Doppler has range resolution.

A

true

67
Q

T/F? Color Doppler is not subject to aliasing.

A

FALSE, is too

68
Q

T/F? Color Doppler measures average velocities.

A

true

69
Q

Pulsed and continuous wave Doppler report __ velocities.

A

peak

70
Q

This is displayed as a vertical bar of various colors, with a black region in the center, during color flow imaging.

A

the dictionary, or lookup table

71
Q

These are the two most commonly used dictionaries in color flow.

A
1. velocity mode

2. variance mode

72
Q

The colors on the color flow dictionary provide information about __ and __.

A

flow direction and velocity

73
Q

The black region in the middle of the color ma indicates…

A

no doppler shift.

74
Q

A

variance mode

75
Q

Variance mode provides information on…

A

direction, speed, and laminar vs turbulent flow.

76
Q

Colors on the left side of a variance mode dictionary indicate __ flow.

A

laminar

77
Q

Colors on the right side of a variance mode dictionary indicate __ flow.

A

turbulent

78
Q

This is a collection of multiple ultrasound pulses used to accurately determine blood velocities.

A

packet or ensemble

79
Q

What are the advantages of larger doppler packets?

A
1. more accurate velocity measurement

2. increased sensitivity to low flow

80
Q

What are the disadvantages of larger doppler packets?

A
1. more time needed to acquire data
2. reduced frame rate
3. decreased temporal resolution
81
Q

This is non-directional color Doppler.

A

power Doppler

82
Q

Power Doppler is also known as…

A

energy mode or color angio.

83
Q

T/F? Power Doppler does not evaluate speed or direction.

A

true

84
Q

What are the advantages of power mode?

A
1. increased sensitivity to low flow or velocity (venous)
2. unaffected by Doppler angles (unless it’s 90 exactly)
3. no aliasing, since velocity is ignored
85
Q

What are the disadvantages of power mode?

A
1. no measurement of velocity or direction
2. lower frame rates
3. susceptible to flash artifact
86
Q

Low frequency Doppler shift artifacts are called…

A

clutter.

87
Q

Low frequency color Doppler shift artifacts are called…

A

ghosting artifact.

88
Q

This is used to eliminate low frequency Doppler shifts from moving anatomy rather than from moving blood cells.

A

wall filter

89
Q

Wall filters are also known as…

A

high pass filters.

90
Q

This special form of ‘mirror image’ artifact arises only with spectral Doppler.

A

crosstalk

91
Q

Crosstalk results from either…

A
1. Doppler gain set too high

2. incident angle near 90

92
Q

This is a tool that breaks the complex signal into its basic ‘building blocks’ and identifies the individual velocities that make up the reflected Doppler signal.

A

Spectral analysis

93
Q

The two methods of spectral analysis currently used are…

A
1. fast fourier transform (FFT)

2. autocorrelation

94
Q

This is a digital technique, used to process both pulsed and continuous wave Doppler signals.

A

Fast Fourier Transform (FFT)

95
Q

What are the advantages of FFT?

A
1. exceedingly accurate

2. displays all individual velocity components

96
Q

The spectral display of an FFT distinguishes __ flow from __ flow.

A

laminar, turbulent

97
Q

A wider range of velocities and shift within a FFT sample volume as seen during turbulent flow is called…

A