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Vascular II & Physics II > Physics Ch. 19 & 20 > Flashcards

Physics Ch. 19 & 20 Flashcards

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1
Q

A change in frequency that comes from motion between sound source and the receiver as they move closer and farther apart

A

Doppler shift

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2
Q

Another name for doppler shift

A

doppler frequency

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3
Q

What is doppler used to measure

A

velocity of blood in the circulation

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4
Q

Process of extracting the low doppler frequency change from the transducers transmitted frequency

A

demodulation

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5
Q

Doppler shift (HZ)=

A

reflected frequency - transmitted frequency

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6
Q

Doppler shifts are in the _____ range of frequencies (_______)

A

audible, 20Hz-20kHz

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7
Q

Doppler shifts are created when transmitted sound wave strikes

A

moving red blood cells

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8
Q

Blod flow moving toward the transducer is

A

positive doppler shift

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9
Q

Positive doppler shift: the _____ frequency is HIGHER than the _____ frequency

A

reflected, transmitted

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10
Q

Blood flow is moving away from the transducer

A

negative doppler shift

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11
Q

Negative doppler shift: the reflected frequency is _____ than the transmitted frequency

A

lower

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12
Q

Speed is _____ only

A

magnitude

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13
Q

Velocity is ______ and ______

A

magnitude, direction

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14
Q

Doppler shift is directly related to

A

velocity, frequency, cosine

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15
Q

Doppler shift is inversely related to

A

speed of sound in soft tissue

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16
Q

The faster the velocity, the _____ the doppler shift

A

greater

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17
Q

What is the doppler equation

A

2 x vel of blood x transducer frequency x cosine / prop speed

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18
Q

Why is there a 2 in the doppler equation

A

First when sound from transducer hits the moving blood cells / Second when the transducer receives the returning sound wave

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19
Q

Doppler shift is measured in units of

A

frequency

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20
Q

Velocity is measured in units of

A

cm/sec

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21
Q

If the transducers frequency is doubled, the measured ______ will also be doubled

A

doppler shift

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22
Q

What about velocity changes with transducer frequency

A

the calculated velocities will be the same regardless of the frequency of the transducer

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23
Q

The measurement of the doppler depends on the relationship between the

A

direction of blood flow and direction in which the sound wave propagates

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24
Q

When the blood cells are moving parallel to the sound beam (__ to __) the

A

0 degrees- 180 degrees, entire velocity is measured and 100% accurate

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25
Q

When blood cells are moving perpendicular (____) to the sound beam, there is

A

no doppler shift and no velocity measurement is attainable

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26
Q

If the sound beam and flow direction are not parallel, only a percentage of the true velocity is measured and that depends on the

A

cosine of the angle between the sound beam and the direction of flow

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27
Q

Measured velocity=

A

true velocity x cosine

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28
Q

Positive and negative doppler shift. Flow toward and away from the transducer

A

bidirectional doppler

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29
Q

Signal processing technique for bidirectional doppler

A

phase quadrature/quadrature detection

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30
Q

Doppler that requires TWO crystals

A

continuous wave doppler

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31
Q

What do the two CW doppler crystals do

A

one constantly transmits and the other constantly receives

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32
Q

What is the advantage of CW

A

ability to accurately measure very high velocities

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33
Q

Disadvantages of CW and what is the name for it

A

cannot determine exact location of the highest velocity, range ambiguity

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34
Q

Reflections created during CW from blood cells located deeper will have

A

lower amplitude (weaker signal) than reflections from shallower depths

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35
Q

What are CW transducers also called

A

dedicated CW transducer, blind transducer, pedoff transducer

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36
Q

CW transducers do not have

A

backing material

37
Q

What are the 4 qualities of a dedicated CW transducer

A

undampened transmitted signal, narrow bandwidth, high Q factor, higher sensitivity

38
Q

Simultaneous anatomic imaging and doppler is called

A

duplex imaging

39
Q

Only one crystal is necessary, alternates between sending and receiving

A

Pulsed wave doppler

40
Q

2 advantages of PW

A

select exact location for velocity measurement / use of sample volume or gate

41
Q

When choosing the exact location for PW, what is this called

A

range resolution, range specificity, range specific

42
Q

What does the sample volume/gate use

A

time of flight calculation

43
Q

What is the disadvantage of PW

A

inaccurate measurement of high velocity signals (aliasing)

44
Q

PW doppler transducers have backing material so they have

A

low Q factor, low sensitivity, wide bandwidth

45
Q

Doppler gain settings alter the gray scale content of the spectral display

A

spectral doppler gain

46
Q

Spectral doppler wall filters selectively eliminates ____ frequency doppler shifts near the ____ of the spectral display

A

low, baseline

47
Q

The wall filter does not affect the appearance of

A

higher velocity flows

48
Q

Most common error associated with doppler ultrasound

A

aliasing

49
Q

An alias is a ______ which is very _____ velocities in one direction are ____ displayed as going in the ______ direction

A

false identity, high, incorrectly, opposite

50
Q

The very top of the display is called

A

nyquist limit

51
Q

The part of the spectrum appearing at the bottom is called

A

aliasing

52
Q

Aliasing occurs when the

A

doppler PRF is too low in comparison to the measured blood velocities (nyquist limit surpassed)

53
Q

Nyquist limit=

A

PRF/2

54
Q

highest doppler shift or velocity that can be measured without the appearance of aliasing

A

nyquist limit

55
Q

Two ways to avoid aliasing

A

raise the nyquist limit (PRF), reduce the doppler shift

56
Q

The sampling rate of PW doppler is the

A

PRF

57
Q

When the sample volume is deep, the PRF is

A

low

58
Q

Deeper sample volume shave a lower _____ and create _____

A

PRF, aliasing

59
Q

When the sampler volume is shallow, the PRF is _____, Nyquist limit is _____

A

high, high

60
Q

Five techniques to avoid/correct aliasing

A
  1. adjust scale (PRF) to max 2. Use a different u/s window and shallower sam volume 3. lower frequency trans 4. adjust baseline 5. use cw doppler
61
Q

Gray shades of spectral display are related to

A

amplitude of reflected signal, number of blood cells creating the reflection

62
Q

Velocity info is coded into colors and superimposed on a 2D gray scale anatomic image

A

color flow doppler

63
Q

Color doppler provided info regarding ______ and is considered _____

A

direction of flow, semi-quantitative

64
Q

Color doppler reports/measures ____ or ____ velocities

A

average, mean

65
Q

Two most commonly used maps/dictionaries are called

A

velocity mode, variance mode

66
Q

The colors provide info on flow direction and mean velocity and is shown on the color map in which direction

A

velocity mode, top to bottom

67
Q

Provides more info, can distinguish between laminar and turbulent flow. What direction is the color map read

A

Cariance mode, side to side

68
Q

The multiple ultrasound pulses for blood velocities is called

A

packet/ensemble

69
Q

To correct aliasing on color doppler you

A

increase scale/PRF/Nyquist limit

70
Q

What does the color look like with aliasing

A

color wrap around reds to blues

71
Q

What does color look like with flow reversal

A

red to black to blue

72
Q

The wall filter selectively eliminateds _______ doppler shifts. The wall filter leaves the _________ unchanged.

A

low frequency, high velocity flows

73
Q

Identifies only the presence of a doppler shift

A

power doppler

74
Q

Does power doppler evaluate velocity or direction

A

no

75
Q

Power doppler is also called

A

energy mode or angio

76
Q

In power mode, the amplitude of the reflection is directly related to the

A

number of moving blood cells

77
Q

Advantages of power mode

A

increased sensitivity to low flow, unaffected dopp angles, no aliasing

78
Q

Disadvantage to power mode

A

no velocity or flow direction

79
Q

On spectral analysis, the artifacts are called

A

clutter

80
Q

With color doppler, the artifacts are called

A

ghosting

81
Q

How do we eliminate ghosting or clutter artifacts

A

wall filter

82
Q

Used to eliminate low frequency doppler shifts from moving anatomy rather than from moving blood cells (“reject”)

A

wall filter

83
Q

Special form of mirror image artifact that only arises with spectral doppler

A

crosstalk

84
Q

Appears as an identical doppler spectrum both above and below the baseline

A

crosstalk

85
Q

Tool that breaks the complex signal into basic building blocks and identifies the individual velocities that make up the reflected doppler signal

A

spectral analysis

86
Q

What are the two methods of spectral analysis

A

fast fourier transform (FFT), autocorrelation

87
Q

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

A

fast fourier transform

88
Q

Spectral display of an FFT distinguishes

A

laminar flow from turbulent flow

89
Q

Digital technique used to analyze color doppler, less accurate but faster

A

autocorrelation

Vascular II & Physics II (21 decks)

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