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Ultrasound Physics > Chapter 19 > Flashcards

Chapter 19 Flashcards

Doppler & color doppler

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1
Q

Doppler shift is the apparent change in the ____ of a wave as a result of relative motion between the sound source and the observer.

A

Frequency

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2
Q

____ ____ is the principle used to measure the velocity of blood moving in the body.

A

Doppler shift

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3
Q

Doppler Shifts are created when transmitted sound waves strike moving ____ ____ ____.

A

Red blood cells

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4
Q

What is the equation for doppler shift?

A

Doppler shift (Hz) = reflected freq. – transmitted freq.

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5
Q

With a positive doppler shift, the red blood cells are moving ____ the transducer.

A

Towards

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6
Q

With a negative doppler shift, the red blood cells are moving ____ the transducer.

A

Away from

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7
Q

Doppler frequencies indicate ____ NOT speed.

A

Velocity

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8
Q

____ is a magnitude, indicates distance but not direction. Units are cm/sec.

A

Speed

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9
Q

____ is a magnitude and a direction (north, south, towards, away).

A

Velocity

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10
Q

The equation for velocity is:

A

Doppler shift x (1540 m/s) / 2 x transducer frequency x cosine angle

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11
Q

Doppler shift is ____ related to the velocity of the blood cells.

A

Directly

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12
Q

Doppler shift is ____ related to the transmitted frequency.

A

Directly

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13
Q

Doppler shift is ____ related to the Doppler angle.

A

Inversely

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14
Q

If the sound beam and flow direction are not parallel, the percentage of the true velocity that is measured depends on the ____ between the sound beam and the direction of motion.

A

Cosine of the angle

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15
Q

Doppler shift is ____ related to the cosine of the angle between flow direction and direction of sound.

A

Directly

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16
Q

If flow is perpendicular (90˚), then the cosine = ____.

A

0

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17
Q

With flow parallel to the sound beam, the angle would be ____ or ____.

A

0° or 180°

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18
Q

With flow perpendicular to the sound beam, the angle would be ____.

A

90°

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19
Q

____ doppler distinguishes the presence and direction of flow.

A

Bidirectional

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20
Q

Most common clinical Doppler devices are ____.

A

Bidirectional

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21
Q

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

A

Phase quadrature

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22
Q

Continuous wave doppler requires how many crystals in the transducer?

A

Two

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23
Q

Main advantage of ____ doppler is its ability to accurately measure very high velocities.

A

CW

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24
Q

The main disadvantage of CW is ____ ____, which is the inability to determine the exact location of the moving red blood cells that are creating the waveform.

A

Range ambiguity

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25
Q

Pulsed wave doppler requires how many crystals in the transducer?

A

One

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26
Q

A major advantage for ____ doppler is range resolution.

A

PW

27
Q

____ ____ is the ability to determine the exact location of the moving red blood cells that are creating the waveform.

A

Range resolution

28
Q

Aliasing exists only with ____ Doppler.

A

PW

29
Q

____ is when the PW Doppler sampling rate is too low in comparison to measured blood velocity, therefore cells moving at high velocities are displayed as moving in the wrong direction.

A

Aliasing

30
Q

____ ____ is the highest Doppler velocity that can be measured without the appearance of aliasing.

A

Nyquist limit

31
Q

How to you calculate the nyquist limit?

A

PRF/2

32
Q

Higher frequency transducers create ____ aliasing because they create higher Doppler shifts

A

More

33
Q

Lower frequency transducers create ____ aliasing because they create lower Doppler shifts.

A

Less

34
Q

What are the five techniques that may be used to avoid aliasing?

A
  1. Adjust the waveform scale to its maximum
  2. Move the baseline shift up or down so that the entire waveform fits in the appropriate area
  3. Select a new ultrasound view with a shallower sample
  4. Select a lower frequency transducer
  5. Use continuous wave Doppler
35
Q

The grey shades on a Doppler spectrum are related to the ____ of the reflected signal, or number of ____ creating the reflection.

A

Amplitude; redblood cells

36
Q

____ imaging is simultaneous anatomic imaging (2D greyscale image) and Doppler.

A

Duplex

37
Q

Best type of transducers for duplex imaging are ____.

A

Arrays

38
Q

____ doppler simply measures the presence of moving blood cells by detecting a Doppler shift. Does not distinguish direction of flow.

A

Power

39
Q

____ dopper is a form of two-dimensional Doppler. The velocity of blood flow is coded into colors and superimposed on a 2D greyscale, anatomic image.

A

Color flow doppler

40
Q

Color Doppler reports ____ velocities.

A

Average

41
Q

Pulsed and continuous wave doppler report ____ velocities.

A

Peak

42
Q

The colors in a velocity mode map present information on flow ____.

A

Direction

43
Q

The black region in the middle indicates ____ Doppler shift.

A

No

44
Q

The colors above the black region indicate blood cells moving ____ the transducer (positive Doppler shifts).

A

Toward

45
Q

The colors below the black region indicate blood cells moving ____ the transducer (negative Doppler shifts).

A

Away from

46
Q

Colors closer to the black region indicate ____ velocities, while colors further from the black region indicate ____ velocities.

A

Lower; higher

47
Q

Top and bottom (yellow and green on bar to left) represent the ____ ____.

A

Nyquist limit

48
Q

The ____ maps display different colors side to side.

A

Variance

49
Q

With variance maps, colors from the left side of the map indicate ____ flow.

A

Laminar

50
Q

With variance maps, colors from the right side of the map indicate ____ flow.

A

Turbulent

51
Q

With color Doppler, multiple ultrasound pulses are used to accurately determine blood cell velocities. These multiple pulses are called a ____ or ____.

A

Packet or ensemble

52
Q

On spectral displays (doppler graph), the low frequency doppler shift artifacts are called ____.

A

Clutter

53
Q

On color doppler, the low frequency doppler shift artifacts are called ____.

A

Ghosting

54
Q

____ ____ (aka high pass filters) eliminate low frequency Doppler shifts from moving anatomy rather than blood flow.

A

Wall filters

55
Q

Crosstalk is a special form of mirror image artifact that arises only with ____ doppler.

A

Spectral

56
Q

____ appears as an identical Doppler spectrum both above and below the baseline.

A

Crosstalk

57
Q

____ ____ 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

58
Q

Two methods of spectral analysis are:

A
  • Fast Fourier Transform (FFT)
  • Autocorrelation
59
Q

Fast Fourier Transform (FFT) is a digital (computer-based) technique used to process both ____ and ____ wave doppler signals.

A

Pulsed and continuous

60
Q

Because ____ displays all the individual frequencies, the spectral display can distinguish laminar flow from turbulent flow.

A

FFT

61
Q

Autocorrelation is the digital technique used to analyze ____ doppler. It determines the mean velocity.

A

Color flow

62
Q

____ is used to analyze color Doppler because of the huge amounts of data that is processed.

A

Autocorrelation

63
Q

Autocorrelation is ____ accurate than FFT but ____ at processing large amounts of data.

A

Less; faster

Ultrasound Physics (11 decks)

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