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Ultrasound Physics > Doppler > Flashcards

Doppler Flashcards

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
duty factor in CW
1 or 100%
26
is CW an imaging trx?
no
27
advantage of CW doppler
sensitive to high velocities
28
disadvantages of CW doppler
range ambiguity / | deep reflectors have a low amplitude and may falsely represent fewer reflectors
29
duplex imaging
2D and doppler
30
dedicated CW / PEDOF
``` 2 semicircular crystals with no backing material undampened signal narrow bandwidth high Q factor high sensitivity ```
31
Doppler shift is the ___ of two frequencies
difference
32
if the frequency of a sound wave changes when there is motion between the sound source and receiver, what other parameters change
wavelength and period
33
what's the problem with continuous wave doppler
range ambiguity
34
can you elicit a Doppler shift with a non directional doppler?
yes
35
number of crystals in PW
1
36
does PW have range ambiguity or range resolution
range resolution
37
what does sample volume calculate
time of flight
38
what does range resolution mean
you can choose the location for sample volume
39
PW is used to
create images
40
do PW doppler try have backing material?
yes
41
is Q factor high or low in PW
low
42
is bandwidth wide or narrow in PW
wide
43
is PW highly sensitive?
no
44
imaging at ___ degrees creates optimal images in PW
90
45
imaging at __ degrees is best for velocity measurements in PW
0
46
disadvantages of PW
aliasing
47
defines when aliasing will occur
nyquist limit
48
when will aliasing occur
when the f>half the PRF
49
as PRF goes down, likelihood to alias ___
increases
50
low sampling rate creates _______ display
erroneous
51
increased sample volume depth = _____ nyquist limit
lower
52
sampling rate is the same thing as...
PRF
53
shallow sample volume = ___ PRF
high
54
with deep sample volume, aliasing is (more/less) likely
more
55
relationship between doppler f and transducer f
direct
56
are low f trx more or less likely to alias
less
57
how to avoid aliasing
``` adjust scale adjust baseline use low f trx obtain image at lowest depth use CW ```
58
gray shades of a spectrum are related to:
``` amplitude of reflected signal / # of RBC creating the reflection ```
59
Doppler shift produces info about...
blood flow velocity
60
units of Doppler effect
change in frequency in Hz
61
which doppler has a high Q factor
CW
62
relationship between depth and PRF
inverse
63
fast moving blood is ___ likely to alias
more
64
why do we need perpendicular incidence in color doppler
we need an angle other than 90 to see color
65
if we see grayscale noise in spectral doppler, the gain is
too high
66
when too much aliasing occurs in color doppler, adjust the ___
scale
67
when the door scale is TOO high, what happens to the color
we lose important color (removes low flow)
68
what does wall filter eliminate
low f doppler shifts fixes "ghosting" reduces 'clutter'
69
broad range of colors indicates
turbulent flow
70
if doppler is too bright, adjust the
gain
71
color map with only red and blue shown
velocity map
72
what does it mean when a color doppler turns black
no flow / 90 degrees
73
bright red and yellow doppler indicates what type of doppler
power doppler
74
another name for spectral doppler mirror
crosstalk
75
how is color doppler processed
autocorrelator
76
how is spectral doppler processed
FFT
77
does color doppler have range resolution?
yes
78
relationship between color doppler packet size and frame rate? accuracy?
inverse, direct
79
turbulent flow is shown on what side of a variance map
right side
80
does power doppler alias?
no

Ultrasound Physics (24 decks)

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