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Ultrasound Physics > Doppler > Flashcards

Doppler Flashcards

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1
Q

change in frequency of a sound wave due to motion between source of sound and its receiver

A

doppler effect

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2
Q

difference between the transmitted and received frequencies

A

doppler shift

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3
Q

received > transmitted

A

positive

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4
Q

transmitted > received

A

negative

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5
Q

relationship between blood cell velocity and Doppler shift

A

direct

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6
Q

Doppler shift equation

A

reflected f - transmitted f

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7
Q

Doppler shift is within audible range of

A

20-20kHz

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8
Q

the process of extracting the doppler shift

A

demodulation

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9
Q

blood moving toward transducer elicits a

A

positive doppler shift

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10
Q

blood moving away from the transducer elicits a

A

negative doppler shift

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11
Q

true velocity x cosine of beam angle = ?

A

measured velocity

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12
Q

what does true velocity depend on

A

cosine of beam angle and direction of flow

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13
Q

distance RBC travels divided by speed

A

speed

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14
Q

defines magnitude and direction of travel

A

velocity

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15
Q

what does the 2 stand for in the doppler equation

A

double Doppler shift (one is transmitted, one is received)

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16
Q

relationship between Doppler shift and transducer frequency

A

direct

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17
Q

relationship between Doppler shift and speed

A

inverse

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18
Q

is there a Doppler shift when RBC aren’t moving?

A

no

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19
Q

a doppler that senses Doppler shift but does not provide any information about direction

A

nondirectional doppler

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20
Q

what does non-coherent mean

A

can’t tell if sound beam is coming toward or away from us

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21
Q

bidirectional doppler can distinguish between ___

A

positive and negative doppler shifts

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22
Q

technique used to process bidirectional doppler

A

phased quadrature

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23
Q

what do you called phased quadrature that detects alias

A

quadrature detection

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24
Q

of crystals in CW doppler

A

2

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25
Q

duty factor in CW

A

1 or 100%

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26
Q

is CW an imaging trx?

A

no

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27
Q

advantage of CW doppler

A

sensitive to high velocities

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28
Q

disadvantages of CW doppler

A

range ambiguity /

deep reflectors have a low amplitude and may falsely represent fewer reflectors

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29
Q

duplex imaging

A

2D and doppler

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30
Q

dedicated CW / PEDOF

A 
2 semicircular crystals with no backing material
undampened signal
narrow bandwidth
high Q factor
high sensitivity
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31
Q

Doppler shift is the ___ of two frequencies

A

difference

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32
Q

if the frequency of a sound wave changes when there is motion between the sound source and receiver, what other parameters change

A

wavelength and period

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33
Q

what’s the problem with continuous wave doppler

A

range ambiguity

34
Q

can you elicit a Doppler shift with a non directional doppler?

A

yes

35
Q

number of crystals in PW

A

1

36
Q

does PW have range ambiguity or range resolution

A

range resolution

37
Q

what does sample volume calculate

A

time of flight

38
Q

what does range resolution mean

A

you can choose the location for sample volume

39
Q

PW is used to

A

create images

40
Q

do PW doppler try have backing material?

A

yes

41
Q

is Q factor high or low in PW

A

low

42
Q

is bandwidth wide or narrow in PW

A

wide

43
Q

is PW highly sensitive?

A

no

44
Q

imaging at ___ degrees creates optimal images in PW

A

90

45
Q

imaging at __ degrees is best for velocity measurements in PW

A

0

46
Q

disadvantages of PW

A

aliasing

47
Q

defines when aliasing will occur

A

nyquist limit

48
Q

when will aliasing occur

A

when the f>half the PRF

49
Q

as PRF goes down, likelihood to alias ___

A

increases

50
Q

low sampling rate creates _______ display

A

erroneous

51
Q

increased sample volume depth = _____ nyquist limit

A

lower

52
Q

sampling rate is the same thing as…

A

PRF

53
Q

shallow sample volume = ___ PRF

A

high

54
Q

with deep sample volume, aliasing is (more/less) likely

A

more

55
Q

relationship between doppler f and transducer f

A

direct

56
Q

are low f trx more or less likely to alias

A

less

57
Q

how to avoid aliasing

A 
adjust scale
adjust baseline
use low f trx
obtain image at lowest depth
use CW
58
Q

gray shades of a spectrum are related to:

A 
amplitude of reflected signal /
# of RBC creating the reflection
59
Q

Doppler shift produces info about…

A

blood flow velocity

60
Q

units of Doppler effect

A

change in frequency in Hz

61
Q

which doppler has a high Q factor

A

CW

62
Q

relationship between depth and PRF

A

inverse

63
Q

fast moving blood is ___ likely to alias

A

more

64
Q

why do we need perpendicular incidence in color doppler

A

we need an angle other than 90 to see color

65
Q

if we see grayscale noise in spectral doppler, the gain is

A

too high

66
Q

when too much aliasing occurs in color doppler, adjust the ___

A

scale

67
Q

when the door scale is TOO high, what happens to the color

A

we lose important color (removes low flow)

68
Q

what does wall filter eliminate

A

low f doppler shifts
fixes “ghosting”
reduces ‘clutter’

69
Q

broad range of colors indicates

A

turbulent flow

70
Q

if doppler is too bright, adjust the

A

gain

71
Q

color map with only red and blue shown

A

velocity map

72
Q

what does it mean when a color doppler turns black

A

no flow / 90 degrees

73
Q

bright red and yellow doppler indicates what type of doppler

A

power doppler

74
Q

another name for spectral doppler mirror

A

crosstalk

75
Q

how is color doppler processed

A

autocorrelator

76
Q

how is spectral doppler processed

A

FFT

77
Q

does color doppler have range resolution?

A

yes

78
Q

relationship between color doppler packet size and frame rate? accuracy?

A

inverse, direct

79
Q

turbulent flow is shown on what side of a variance map

A

right side

80
Q

does power doppler alias?

A

no

Ultrasound Physics (24 decks)

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