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CNIH > PHY- Doppler > Flashcards

PHY- Doppler Flashcards

1
Q

define Doppler effect

A

change in frequency caused by the motion of a source, reflector or receiver

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2
Q

examples of doppler affect? (4)

A
  1. weather forecasting
  2. police radar
  3. door openers
  4. burgler alarms
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3
Q

Define dopper shift and give examples

A
  • quantification of the change in frquency

getting closer, frequency ↑ (positive shift)
getting farther, frequency ↓ (negative shift)

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4
Q

Doppler 4 steps?

A
  1. Transducer sends a pulse to moving object
  2. transducer receives the new frequency and calculates doppler shift doppler shift
  3. doppler shift depends on the objects velocity
  4. machine calculated speed based on doppler shift
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5
Q

what does the doppler shift depend on?

A
  • Objects velocity

- cosine of doppler angle

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6
Q

if the angle of interrogation is non-zero what will occur?

A

Lesser dopper shift with occur

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7
Q

why do we incorporate cos 0 to dopper shift?

A

to compensate for the lesser shift

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8
Q

What is doppler angle?

A

the angle of incident beam to the direction of blood flow

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9
Q

cosine 0, 30, 60, 90 degrees?

A

cos 0= 1
cos 30= 0.87
cos 60= 0.5
cos 90= 0

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10
Q

to achieve an angle close to zero the sonographer must?

A
  • heel-toe

- phase (steer)

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11
Q

define doppler ultrasound characteristics (4)

A

presence, speed, character and direction of blood flow

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12
Q

what are the 3 characteristics of doppler ultrasound display?

A
  1. colour
  2. spectral
  3. audible
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13
Q

what information are we getiing from colour doppler (4)

A
  1. presence
  2. speed
  3. character
  4. direction
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14
Q

how is doppler shift detected?

A
  • beam former sends digitized voltages to signal processor

- signal processor detect dopper shifted echoes using autocorrelation

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15
Q

what detects shifted echos and using what?

A
  • signal processor detects doppler shifted echos using autocorrelation
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16
Q

define autocorrelation

A

mathematical technique that determines mean and variance of doppler shift signal

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17
Q

what 4 things does autocorrelation determine?

A
  1. mean of doppler shift signal
  2. variance of doppler shift signal
  3. power
  4. sign
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18
Q

how many pulses are sent out per scan line?

A

3-32

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19
Q

pros and cons of multiple pulses being sent out per scan line

A

pros: increased accuracy and sensitivity (picking out weaker echoes/shifts)
cons: decreased frame rate

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20
Q

what does autocorrelation calculate and display? (4)

A
  • average velocity
  • distribution of velocities
  • strength of echoes
    sign -/+
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21
Q

what is power? what is it related to?

A
  • the intensity of an echo

- related to the amplitude

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22
Q

what does power depend on? (3)

A
  • reflectors
  • impedance
  • concentration of RBC’s
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23
Q

more relection =

A

more reflection, more echo

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24
Q

higher delta z =

A

more echo

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25
Q

higher concentration of RBC’s =

A

more reflectors, more echo

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26
Q

what does power doppler use?

A

ONLY uses the power/strength of doppler shifts

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27
Q

pros of power doppler?

A
  • increased sensitivity
  • no angle dependence
  • no aliasing
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28
Q

cons of power doppler? (4)

A
  • no direction
  • no flow sleed
  • no flow character info
  • cannot detect a stenosis
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29
Q

3 colour display parameters?

A
  1. hue
  2. saturation
    3, luminance
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30
Q

what is saturation?

A

richness of colour

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31
Q

what is luminance?

A

brightness of colour

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32
Q

9 colour controls?

A
  1. box
  2. colour map
  3. colour invert
  4. baseline
  5. PRF
  6. gain
  7. wall filter
  8. ensemble length
  9. priority
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33
Q

baseline AKA?

A

zero point

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34
Q

to show more positive flows what should you do to the baseline?

A

move it down

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35
Q

changing PRF will change our?

A

scale

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36
Q

what does lowering the PRF do?

A
  • allows to pick up slower flow

- increases chance of aliasing

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37
Q

aliasing depends on?

A

Nyquist limit

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38
Q

pros of aliasing?

A

can highlight the fastest speeds within a stenosis

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39
Q

where in the instrument does gain occur?

A

amplifiers of beam former

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40
Q

what is wall filter?

A

cutting off slower flows/tissue motion

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41
Q

ensemble length AKA?

A

packet size

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42
Q

what is ensemble length?

A

number of pulses used for each colour scan line

43
Q

priority AKA?

A

threshold

44
Q

what is priority?

A
  • echos below cut-off amplitude will show colour

- stronger echoes show as grayscale

45
Q

if priority iof set too low what occurs?

A
  • noise or artifacts within the vessel are displayed with little colour
46
Q

if priority of set too high what occurs?

A

fills the vessel with colour

- when there is a low signal-to-noise ratio

47
Q

4 colour limitaitons?

A
  1. angle dependence
  2. low FR
  3. lack of spectral info
  4. sonographer skill
48
Q

what is duplex scanning?

A
  • doppler = gray scale imaging
  • Transducer does one at a time
  • simultaneous does exist but decreased FR- rapidly switches between the two
49
Q

In practice, approximately _____ pulses are required to obtain one line of color Doppler information?

A

10

50
Q

Lack of color in a vessel with blood flow may be attributable to ______ (3)

A
  • low colour gain
  • high wall filter setting
  • low priority setting
51
Q

Increasing ensemble length ____ color sensitivity and accuracy and ________ FR

A
  • improves, decreases
52
Q

What color control helps with clutter?

A

wall filter

53
Q

Color map baselines are always represented by what color?

A

black

54
Q

steering the color window to the right or left changes _____? (2)

A
  • doppler shift

- doppler angle

55
Q

In a single frame, color can be different ( red and blue) in a vessel because of ____? (4)

A
  • Vessel curvature
  • Sector format
  • Helical flow
  • Diastolic flow reversal
56
Q

Doppler power imaging indicates the _______ of flow

A

presence

57
Q

what info are we getting from spectral doppler? (4)

A
  1. presence
  2. direction
  3. character
  4. speed
58
Q

Pulse generates pulses _____ cycles long

A
59
Q

what determines doppler shift accurately?

A

longer pulse

60
Q

spectral doppler characteristics? (3)

A
  1. pulser
  2. detector
  3. spectrum analyzer
61
Q

the detector is part of what element?

A

signal processor

62
Q

function of detector?

A
  • echo voltages are amplified

- doppler shifts determined by comparing to pulser frequency

63
Q

2 things that contribute to the detecor?

A
  1. mixer (fR+ fT) and (fR-fT)

2. filter (gets rid of sum)

64
Q

function of spectrum analyzer?

A

generates doppler shift spectral displays using fast Fourier transform

65
Q

the spectrum analyzer generates doppler shift spectral displays using?

A

fast fourier transform

66
Q

what is fast fourier transform?

A

mathematical technique for spectral doppler

** remember autocorrelation is the mathematical tequnique for colour doppler

67
Q

The amplitude or power of each Doppler shift is shown as?

A

brightness

68
Q

dark spots on spectral display means that doppler shift is?

A

very weak or nonexistant

69
Q

what is range gating?

A

ability to take motion information from a specific depth

70
Q

gate amplifier is found in?

A

beam former

71
Q

the gate amplifier takes samples from? (2)

A
  1. specific sample volume (gate)

2. specific depth

72
Q

what is gate width?

A

wb

- At the sample volume depth

73
Q

when to use longer gate- gate length?

A

when searching for a vessel or flow location

74
Q

when to use a shorter gate- gate length?

A

for spectral analysis and evaluation

75
Q

a shorter gate improves?

A

the quality of the spectral display

76
Q

What is spectral broadening? when is it seen? what does it cause?

A
  • vertical thickening of the spectral trace
  • seen with wider range of velocities
  • causes narrowing of window
77
Q

reasons for spectral broadening?

A
  • disturbed or turbulent flow
78
Q

what is artificial spectral broadening?

A
  • excessive doppler gain

- excessive sample volume length

79
Q

8 spectral controls?

A
  1. gate size/ sample volume
  2. gain
  3. spectral invert
  4. baseline
  5. PRF
  6. wall filter
  7. angle correct
  8. audio
80
Q

with gain there is potential for?

A
  • amplifications of echos

- potential for noise and spectral broadening

81
Q

increasing angle, decreases?

A
  • doppler frequency
  • velocity
  • makes it seem lower than it is
82
Q

audio- higher frequency =

A

higher pitch

83
Q

what is CW doppler?

A
  • 2 transducer elements- one to send, one to receive
  • very small probe
  • sample volume is large in overlapping area
84
Q

beacuse sample volume is large with CW doppler what occurs?

A
  • poor range resolution and ability to determine depth of reflectors
85
Q

T or F CW doppler can alias?

A
  • False

- no PRF in CW

86
Q

If angle correction is set at 60 degrees but should be zero degrees, the display indicates a flow speed of 100 cm/s
The correct flow speed is _____ cm/s.

A

50

87
Q

If angle correction is set at 0 degrees but should be 60 degrees, the display indicates a flow speed of 100 cm/s
The correct flow speed is _____ cm/s.

A

200

88
Q

If a 5-kHz Doppler shift corresponds to 100 m/s, a 2.5-kHz shift corresponds to ____ m/s

A

50

89
Q

Which of the following is increased if Doppler angle is increased?

a. Aliasing
b. Doppler shift
c. Effect of angle error
d. b and c
e. None of the above

A

effect of angle error

90
Q

Color-Doppler frame rates are ______ gray-scale rates

A

less than

91
Q

Decreased distal resistance normally causes end diastolic flow to ________.

A

increase

92
Q

Flow reversal in diastole indicates ______.

A

high distal resistance

93
Q

T or F With angle correct incorporated, higher flow speed always produces a higher Doppler shift on spectral display.

A

true

94
Q

Higher operating frequency produces a higher Doppler shift on spectral display. T or F

A

true

95
Q

Does higher freq transducer overestimate velocity?

A

no

96
Q

As stenosis progresses, which of the following increases?

a. Lumen diameter
b. Systolic Doppler shift
c. Diastolic Doppler shift
d. Spectral broadening
e. more than one of the above

A

e. (b,c,d)

97
Q

Disturbed flow produces narrower spectrum?

A

false

98
Q

T or F- Turbulent flow produces a narrower spectrum?

A

false

99
Q

If all the cells in a vessel were moving at the same constant speed, the spectral trace would be _____________.

a. thin horizontal line
b. thick horizontal line
c. as in descending aorta
d. tardus parvus
e. depends on velocity

A

thin horizontal line

100
Q

stenosis effect?

A 
Peak systolic flow speed
End diastolic flow speed
Spectral broadening
Window
Envelope
101
Q

T or F: Doppler ultrasound provides information about flow conditions only at the site of measurement.

A

False

102
Q

Doppler signal power (or amplitude) is proportional to _______.

A

cell concentration

103
Q

Compared with Doppler-shift imaging, Doppler-power imaging is _______.

A

More sensitive
Angle independent
Aliasing free
Speed independent

104
Q

Doppler-power imaging indicates (with color) the _____ of the flow.

A

presence

CNIH (69 decks)

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