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DMSO Physics 2 > Doppler > Flashcards

Doppler Flashcards

1
Q

Doppler Shift (Doppler Frequency)

A

The change or variation in the freq of sound as a result of motion between the sound source and the receiver

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2
Q

What is the difference between received and transmitted frequencies?

A

Doppler shift

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3
Q

When reflected frequency is higher than transmitted?

A

positive change

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4
Q

reflected freq is less than transmitted?

A

negative change

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5
Q

Doppler measures _____ not _______

A

frequency shift, not amplitude

velocity, not speed

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6
Q

untis of freq

A

Hz

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7
Q

Typical audible values created when sound reflects off of RBC’s

A

20Hz-20 kHz

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8
Q

flow towards the transducers?

A

increased freq

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9
Q

flow away from the transducers

A

decreased frequencies

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10
Q

frequency shift is related to what?

A

velocity

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11
Q

2 MHz-10 MHz transducers are usedto preform doppler ultrasound studies, but doppler shift ranges from?

A

20Hz-20kHz

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12
Q

The process of extracting the Doppler freq (low) form the transducer frequency (high)?

A

demodulation

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13
Q

Doppler shift=

A

received freq - transmitted freq

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14
Q

doppler equation

A

doppler shift= 2xrefelctor speedxincident frequencyxcos angle/ prop speed

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15
Q

Doppler shift is directly related to:

A

RBC speed, frequency of transducer, cos of angle between flow and sound beam

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16
Q

Doppler shift is inversely related to:

A

speed of sound in the medium

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17
Q

velocity (measured)=

A

true velocityxcos angle

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18
Q

Non-choerent processing used with what

A

uni-directional doppler

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19
Q

ultrasound system that displays real-time images and Doppler simultaneously is called?

A

duplex

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20
Q

Phase quadrature processing used in?

A

bidirectional doppler

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21
Q

number of cyrstals in a CW doppler

A

2

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22
Q

Advantage of CW doppler

A

Able to measure very high velocities

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23
Q

Disadvantage of CW Doppler

A

range ambiguity

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24
Q

Echoes arise from entire length of overlap between the transmit and receive beams

A

range ambiguity

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25
Q

how manycrystals are needed for PW Doppler

A

1

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26
Q

Advantage of PW Doppler

A

Echoes only arise from the area of integration, ample volume or gate. We adjust the receive gate. Range resolution

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27
Q

Disadvantage of PW doppler

A

Aliasing, errors in measuring high velocities

28
Q

High velocity measurements are inaccurate if the pulsed Doppler sampling rate is too low in comparison to measured blood velocity?

A

Aliasing

29
Q

What should be done to improve the ability to measure the max velocity with Doppler?

A

Eliminate aliasing

30
Q

The doppler freq at which aliasing occurs

A

Nyquist limit (nyquist freq)

31
Q

PRF/2

A

Nyquist limit (kHz)

32
Q

Aliasing is more likely to occur with higher or lower frquencies?

A

Higher

33
Q

Five ways to eliminate aliasing

A
  1. adjust scale
  2. select transducers with low freq
  3. select new view with shallower sample volume
  4. use CW doppler
  5. baseline shift
34
Q

PRF and Nyquist limit are lower with shallower or deeper sample volumes?

A

deeper

35
Q

______ sampler volumes (gates) create Doppler spectra with larger, cleaner envelopes

A

smaller

36
Q

Larger sample volumes create doppler sepectra with smaller envelopes known as what?

A

Spectral broadening

37
Q

The horizontial axis of a doppler spectrum is?

A

time

38
Q

The vertical axis of a Doppler spectrum is?

A

doppler shift or velocity

39
Q

relationship between transducer frequency and doppler shift

A

when freq is halved, doppler shift is half

40
Q

Gray shades on a Doppler spectrum are related to:

A

Amplitude of the reflected signal or the number of RBC’s creating the reflection

41
Q

pulsed doppler

A
  1. Min of one crystal
  2. range resolution
  3. limit on max velocity
  4. damped, low Q, wide bandwidth
42
Q

Continuous Doppler

A
  1. min of two crystals
  2. range ambiguity, region of overlap
  3. unlimited max velocity
  4. undamped, high Q, narrow bandwidth
43
Q

imaging transducers

A
  1. normal incidence
  2. higher freq- improved resolution
  3. pulsed wave only
  4. at least 1 crystal
44
Q

Doppler transducers

A
  1. 0 to 180 degrees
  2. lower freq
  3. pulsed or CW
  4. 1 (PW) or 2 (CW) crystals
45
Q

color doppler reports

A

average velocities

46
Q

variance mode

A

color map that varies side to side. left side: laminar right side: turbulent

47
Q

Which setting has the greatest effect on jet size?

A

Color doppler gain

48
Q

Multiple ultrasound pulses are needed to accurately determine RBC velocities by doppler?

A

A packet or ensemble length

49
Q

Advantages of more pulses in the packet

A

greater accuracy of the velocity measurement sensitivity to low flow

50
Q

disadvantages of more pulses in the packet?

A

More time is required to acquire info

frame rate is reduced

temporal resolution is decreased

51
Q

Why does color doppler measure mean velocity?

A

the packet size must balance between accurate velocity measurements and temporal resolution

52
Q

Synonyms for power doppler

A

energy mode or color angio

53
Q

Advantages of power doppler

A
  1. increased sensitivity to low flow
  2. not effected by doppler angle unless 90 degrees
  3. no aliasing
54
Q

limitations of power doppler

A
  1. no measurement of velocity
  2. slower frame rates
  3. susceptible to motion (flash artifact)
55
Q

performed to extract or identify the individual freq making up a complex signal?

A

spectral analysis

56
Q

Spectral analysis method for pulsed or CW doppler

A

Fast Fourier transform

57
Q

spectral analysis for color flow doppler

A

autocorrelation or correlation function

58
Q

FFT and autocorrelation are what type of techniques

A

digital

59
Q

used due to the large amount of Doppler information that requires processing?

A

Autocorrelation

Slightly less accurate, but faster than FFT

60
Q

Can a successful Doppler exam be preformed regardless of a patients hematocrit?

A

yes

61
Q

Ghosting

A

Low velocity motion from pulsating vessel walls can also produce small doppler shifts that bleed into surrounding anatomy

62
Q

High pass filter

A

Eliminates low magnitude Doppler shifts that are created from moving anatomy rather than red blood cells

63
Q

Wall filters are used to reject?

A

Clutter

64
Q

color flash is also called?

A

ghosting

65
Q

Cross talk is in?

A

doppler only

66
Q

Special form of mirror image where the Doppler spectrum appears above and below the baseline?

A

Cross talk

67
Q

Cause of crosstalk

A

Doppler gain set too high

Incident angle near 90 degrees when flow is at focus

DMSO Physics 2 (26 decks)

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