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Doppler physics > Chapter 19 Pt. 2 > Flashcards

Chapter 19 Pt. 2 Flashcards

1
Q

The most common error associated with Doppler Ultrasound

A

Aliasing

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2
Q

High velocity flow in one direction that is incorrectly displayed as traveling in the opposite direction is?

A

Aliasing

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3
Q

The very top of the display is called?

A

Nyquist limit

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4
Q

Part of the spectrum appearing at the bottom

A

Aliasing

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5
Q

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

A

Nyquist frequency (limit)

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6
Q

Nyquist limit is ___________ of the pulse repetition frequency (PRF)?

A

half

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7
Q

Two ways to avoid aliasing are:

A
  1. raise the nyquist limit

2. reduce the Doppler shift

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8
Q

Higher frequency transducers create________ aliasing,

A

more

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9
Q

Higher frequency transducers create _________Doppler shifts and lower frequency transducers create ____ Doppler shifts

A

Higher, lower

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10
Q

5 techniques used to avoid aliasing

A
  1. Adjust the scale to its max
  2. Select a new ultrasonic view with a shallower sample volume
  3. Select a lower frequency transducer
  4. Use baseline shift
  5. Use continuous wave doppler
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11
Q

Color Doppler measures. . .

A

average or mean velocity

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12
Q

Spectral Doppler (continuous and pulsed) measures

A

peak velocity

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13
Q

In Velocity mode the colors above the black stripe indicate?

A

Blood cells moving towards the transducer, Positive Doppler shift

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14
Q

Colors below the black stripe indicate?

A

Blood cells moving away from the transducer, Negative Doppler shift

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15
Q

The black region in the middle of the color map indicates:

A

No Doppler shift

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16
Q

Variance mode distinguishes

A

laminar and turbulent flow

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17
Q

In variance mode, colors of the left side of the map indicate?

A

Laminar flow

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18
Q

In Variance mode, colors on the right side of the map indicate?

A

Turbulent flow

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19
Q

Multiple pulses used in color Doppler to accurately determine blood velocity

A

Packet or ensemble

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20
Q

Power mode is

A

Nondirectional Doppler

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21
Q

Power Doppler is also called

A

energy mode or color angio

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22
Q

On Spectral displays, low frequency Doppler shift artifacts are called

A

Clutter

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23
Q

With color Doppler low frequency Doppler shift artifacts are called?

A

Ghosting

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24
Q

Wall filters are used to eliminate what?

A

Clutter

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25
Q

a special form of “mirror” image artifact, that arises only with spectral Doppler

A

Crosstalk

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26
Q

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

27
Q

Two methods that spectral analysis is currently used for?

A
  1. Fast Fourier Transform (FFT)

2. Autocorrelation

28
Q

A digital technique, used to process both pulsed and continuous wave Doppler signals

A

Fast Fourier Transform (FFT)

29
Q

Two advantages of FFT

A
  • exceedingly accurate

- displays all individual velocity components that make up the complex reflected signal

30
Q

Spectral display of an FFT distiguishes

A

laminar from turbulent flow

31
Q

a wider range of velocities and Doppler shift within the sample volume

A

Spectral broadening

32
Q

a digital technique used to analyze color flow Doppler

A

Autocorrelation

33
Q

Identifies the highest velocity jets anywhere along the length of the ultrasound beam

A

Continuous wave Doppler

34
Q

Accurately identifies the location of flow

A

Pulsed wave

35
Q

Provides two dimensional flow information directly on anatomic image

A

Color flow

36
Q

Used with low velocity or small volume blood flow

A

Power mode

37
Q

With what Doppler modality does Range ambiguity occur?

A

Continuous wave Doppler

38
Q

With what Doppler modality does Range resolution occur?

A

Pulsed wave Doppler, Color Flow, and power mode

39
Q

Doppler modality that is most sensitive?

A

Continuous wave

40
Q

Pulsed wave Doppler is ____________ sensitive?

A

Moderately

41
Q

Moderately sensitive and the size of the color jet is most affected by color Doppler gain settings

A

Color flow

42
Q

What Doppler modality has greater sensitivity than color flow?

A

Power mode

43
Q

What Doppler modalities have Very good temporal resolution?

A

Continuous wave and pulsed wave

44
Q

Color flow has reduced temporal resolution due to ___________?

A

multilple packets

45
Q

What Doppler mode has the lowest temporal resolution?

A

Power mode

46
Q

__________has no aliasing

A

Continuous wave

47
Q

This modality is subject to aliasing

A

Pulsed wave

48
Q

Power mode is subject to __________ artifact, not to aliasing

A

flash

49
Q

Based on pulsed ultrasound, color flow is subject to

A

aliasing

50
Q

Which Doppler measures mean velocities

A

Color flow

51
Q

Which Doppler measures Peak velocities

A

Continuous wave and pulsed wave

52
Q

Which Doppler measures no velocities

A

Power mode

53
Q

Doppler shift is directly related to

A

velocity & transducer frequency

54
Q

Doppler shift is _______________ related to the cosine of the angle between the directions of flow and the direction of sound

A

directly

55
Q

CW transducer do not use __________

A

Backing material

56
Q

No use of backing material results in

A
  • undampened transmitted signal
  • narrow bandwidth
  • high quality factor
  • higher sensitivity
57
Q

CW transducers have ___________and they detect ___________ amplitude reflections and small Doppler shifts

A

increased sensitivity , low

58
Q

Pulsed Doppler Transducers are ________ transducers and contain__________

A

imaging, backing material

59
Q

Since PW transducers have backing material they have

A
  • low quality factor
  • lower sensitivity
  • wide bandwidth pulses
60
Q

Nyquist limit formula

A

nyquist limit(Hz) = PRF (Hz)/2

61
Q
  • slower blood velocity
  • lower frequency
  • shallow gate (high PRF)
A

Less aliasing

62
Q
  • Faster blood velocity
  • Higher frequency
  • deep gate (low PRF)
A

More aliasing

63
Q

Doppler shift formula

A

Doppler shift (Hz)= reflected frequency- transmitted frequency

64
Q

What two techniques to avoid aliasing have no disadvantages?

A

Selecting a new ultrasonic view, and lower frequency tranducer

Doppler physics (2 decks)

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