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Chapter 19 Flashcards

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1
Q

Doppler ultrasound can detect

_

A

The presence,
direction, velocity, and properties of blood
flow in vessels

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2
Q

The Doppler effect is a phenomenon in

which

A

an apparent change in the frequency
of sound is observed if there is relative
motion between the source of the sound and
the receiver

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3
Q

the change in frequency
between the transmitted frequency and the
received frequency

A

Doppler shift

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4
Q

Doppler shifts are created when _

A

transmitted

sound waves strike moving red blood cells

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5
Q

_ doppler shift: when blood cells
move toward the transducer; reflected
intensity is _ than the transmitted
frequency

A

positive

higher

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6
Q

_ doppler shift: when blood cells
move away from the transducer; reflected
intensity is _ than the transmitted
frequency.

A

negative

lower

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7
Q

If the transmitted frequency is higher than the reflected frequency,
what type of shift occurs?

A

negative

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8
Q

If the reflected frequency is higher
than the transmitted frequency,
what type of shift occurs?

A

positive

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9
Q

Doppler frequencies indicate _ not _

A

velocity

speed

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10
Q

Speed or velocity:

Purely magnitude

A

speed

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11
Q

Speed or velocity: Indicates the distance that a red blood cell
moves in 1 second

A

speed

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12
Q

Speed or velocity: cm/s or other units of distance/time

A

speed

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13
Q

Speed or velocity: Magnitude and direction

A

velocity

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14
Q

The doppler equation

A

Doppler shift= (2 X velocity of blood X transducer frequency X cos) / propagation speed

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15
Q

The two in the equation represents

A

that there
are actually two Doppler shifts during an
exam

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16
Q

First doppler shift _

Second doppler shift _

A

when sound strikes moving blood cells

transducers reception of the sound wave from moving red blood cells

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17
Q

Relationship between doppler shift and velocity of RBC’s

A

direct

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18
Q

The faster the velocity, the _ the doppler frequency

A

greater

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19
Q

Modern ultrasound systems actually measure

A

the frequency difference (in hertz) between

received and transmitted waves

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20
Q

The Doppler equation is programmed into the
ultrasound system’s computer. The computer
uses the data to determine _

A

the velocity of blood

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21
Q

Doppler equation programmed into US system: Actual data is _, with units of _. Derived information is _, with units of _

A

frequency
hertz
velocity
m/s

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22
Q

Relationship between doppler shift and frequency of transmitted sound

A

direct

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23
Q

If transducer’s frequency is doubled, the

measured Doppler shift will

A

also be doubled

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24
Q

The measurement of the Doppler frequency

depends on

A

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

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25
Q

When blood cells are moving parallel to the

sound beam, the _ is measured

A

entire velocity

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26
Q

When an angle exists between the direction
of flow and the sound beam, the measured
velocity is _ than the true velocity

A

less

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27
Q

The percentage of the true velocity that is

measured depends on

A

the cosine of the angle
between the sound beam and the direction of
motion.

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28
Q

Angle: 0
Cosine:

A

1.0

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29
Q

Angle: 30
Cosine:

A

0.87

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30
Q

Angle: 60
Cosine:

A

0.5

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31
Q

Angle: 90
Cosine:

A

0

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32
Q

Angle: 120
Cosine:

A

-0.5

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33
Q

Angle: 150
Cosine:

A

-0.87

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34
Q

Angle: 180
Cosine:

A

-1.0

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35
Q

Realtionship between doppler shift and cosine of the angle

A

direct

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36
Q

Relationship between doppler shift and the direction of sound

A

direct

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37
Q

If the cosine Θ is reduced by half, the

measured Doppler shift will _

A

be halved

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38
Q

If flow is parallel to the sound beam, the angle between the direction of motion and sound is

A

0 degrees or 180 degrees

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39
Q

If flow is parallel to the sound beam, the measured and true velocities are _

A

equal

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40
Q

cosine 0 degrees is _, indicating flow _

A

1

toward the transducer

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41
Q

cosine 180 degrees is _, indicating flow _

A

-1

away from the transducer

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42
Q

If flow is perpendicular to the sound beam,

the measured velocity is _. Cosine 90 degrees is _

A

zero

zero

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43
Q

Doppler shifts and velocities cannot be

measured with

A

perpendicular incidence

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44
Q

Most accurate measured velocity

A

Flow is parallel to the sound beam 0 degrees or 180 degrees

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45
Q

if blood moves at a 60° angle to the

beam, the measured velocity is _ the actual velocity. Why?

A

1/2

the cosine of 60 is 0.5

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46
Q

Bidirectional Doppler devices distinguish _

A

the
direction of flow toward or away from the
transducer.

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47
Q

A positive Doppler shift indicates flow _ the transducer

A

toward

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48
Q

A negative Doppler shift indicates flow _ the transducer

A

away from

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49
Q

Audio of bidirectional Doppler requires _

A

headphones or speakers, where sound from one

speaker represents flow towards the transducer, and the other represents flow away from the transducer.

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50
Q

Flow toward the transducer is displayed _ the baseline

A

above

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51
Q

flow away from the

transducer is displayed _ the baseline

A

below

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52
Q

Continuous Wave

Doppler requires _ crystals

A

2

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53
Q

In continuous wave trandsucers, one crystal _ while the other _

A

constantly transmits

continuously receives
reflections from blood cells

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54
Q

Greatest advantage of continuous wave doppler is its ability to _

A

accurately measure very high velocities.

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55
Q

Disadvantages of continuous wave doppler

A

range ambiguity

Lack of TGC

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56
Q

Range ambiguity

A

Exact location of the moving blood cells

cannot be determined

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57
Q

Do continuous wave transducers use backing material?

A

No

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58
Q

Do continuous wave transducers have a matching layer?

A

Yes

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59
Q

In pulsed wave Doppler, _ PZT crystal is

necessary.

A

only one

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60
Q

With pulsed wave doppler, sonographers position _. The US system calculates _

A

a small marker called
the sample volume or
gate on a 2-D image.
time of flight for a sound pulse traveling to and from the gate.

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61
Q

Advantage of pulsed wave doppler:

A

the ability to select the exact location where velocities are measured.

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62
Q

AKA range resolution, range specificity, or

freedom from range ambiguity artifact.

A

the ability to select the exact location where velocities are measured

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63
Q

Disadvantages of pulsed wave doppler

A

Inaccurate measurement of high velocity
signals.
High velocity flow in one direction is incorrectly
displayed as traveling in the opposite direction.

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64
Q

High velocity flow in one direction is incorrectly

displayed as traveling in the opposite direction.

A

Aliasing

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65
Q

Studies that simultaneously perform imaging

and pulsed Doppler are called

A

duplex exams

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66
Q

pulsed wave transducers: _ crystals, contains _, _ Q factor, _ sensitivity, _ bandwith

A 
single
backing material
low
low
wide
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67
Q

Most common error associated with Doppler

ultrasound.

A

Aliasing

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68
Q

Aliasing

A

Very high velocities in one direction are
incorrectly displayed as going in the opposite
direction.

69
Q 
Velocity of blood cells reach 
the very top of the spectral 
display and incorrectly 
wrap around and appear at 
the bottom of the display
A

Aliasing

70
Q

The very top or bottom of the display

A

nyquist limit

71
Q

Can aliasing occur in the opposite direction?

A

Yes

72
Q

Aliasing only occurs with _ doppler

A

pulsed

73
Q

Aliasing occurs when doppler sampling rate is _

A

too low in comparison to the measured blood

velocities

74
Q

Nyquist limit = _ PRF

A

1/2

75
Q

Nyquist limit = _

A

PRF/2

76
Q

Two ways to avoid aliasing:

A

Raise the Nyquist limit

Reduce the Doppler shift

77
Q

When the sample volume is deep, the

PRF is _ and the nyquist limit is _. This can create _

A

low
low
aliasing

78
Q

When the sample volume is shallow,

the PRF is_ and the nyquist limit is _. The system

A

high
high
accurately measures
high velocity without aliasing.

79
Q

_ frequency transducers create more

aliasing.

A

higher

80
Q

Relationship between doppler shift and transducer frequency

A

directly

81
Q

At a particular velocity, higher frequency

transducers create _ doppler shifts and lower frequency transducers create _doppler shifts

A

higher

lower

82
Q

Aliasing artifacts are less common with _ frequency transducers due to _

A

lower
the Doppler
shifts being less likely to exceed the Nyquist
limit.

83
Q

Less aliasing: _ velocity, _ frequency transducer, _ gate, _ PRF

A

slower, lower, shallow, higher

84
Q

More alaiasing: _ velocity, _ frequency, _ gate, _ PRF

A

faster, higher, deep, low

85
Q

Five techniques may be used to avoid

aliasing artifact:

A
  1. Adjust the scale to its maximum
  2. Select a new ultrasonic view with a shallower sample volume
  3. Select a lower frequency transducer
  4. Use baseline shift
  5. Use continuous wave Doppler
86
Q

Advanages of adjusting scale to its maximum

A

raises the nyquist limit and aliasing

is less likely to appear

87
Q

Disadvantages of adjusting scale to its maximum

A

higher PRF reduces sensitivity to low velocities.
With very high velocities, aliasing artifact persists,
even when the scale is maximized.

88
Q

If the scale is adjusted to its maximum, the PRF is _

A

also adjusted to its

maximum. (increase PRF increases Nyquist limit)

89
Q

Advantages of selecting a new ultrasonic view with a shallower sample volume

A

PRF is increased, Nyquist limit increased,

aliasing is reduced

90
Q

Disadvantages of selecting a new ultrasonic view with a shallower sample volume

A

None

91
Q

Advantages of selecting a lower frequency transducer

A

Lower doppler shifts occur with lower frequency
transducers and reduces the height of the doppler
spectrum.
Lower doppler shifts are less likely to exceed the
Nyquist limit and less likely to alias

92
Q

Disadvantages of selecting a lower frequency transducer

A

No significant disadvantages other than producing

a lower quality anatomic image

93
Q

Baseline usually appears _

A

in the middle of the display

94
Q

_ simply slides the display baseline up or down so

that the entire velocity scale is devoted to one direction.

A

Baseline shift

95
Q

Advantages of baseline shift

A

High velocity flows are displayed in the proper direction.

Measurements remain accurate even after shifting the baseline

96
Q

Disadvantages of baseline shift

A

Only changes the visual appearance of flow
If audio is used, the sound will still be heard from incorrect
speaker
Will be ineffective when the doppler shift is so high that the
signal completely wraps around itself.

97
Q

Advantages of continuous wave doppler

A

Aliasing never appears

with continuous wave Doppler.

98
Q

Disadvantages of continuous wave doppler

A 
Range ambiguity
Velocities along the entire region of 
overlap between the transmit and receive 
beams blend together to form the 
spectrum
99
Q

Techniques that eliminated aliasing:
Method: Adjust scale
Strategy: _

A

Increase nyquist limit

100
Q

Techniques that eliminated aliasing:
Method: new, shallower view
Strategy: _

A

increase nyquist limit

101
Q

Techniques that eliminated aliasing:
Method: lower transducer frequency
Strategy: _

A

decrease doppler shift

102
Q

Techniques that eliminated aliasing:
Method: zero baseline shift
Strategy: _

A

aliasing remains but display is more appealing

103
Q

Techniques that eliminated aliasing:
Method: Continuous wave doppler
Strategy: _

A

never aliases, but range ambiguity

104
Q

Gray shades
on a doppler
spectrum are
related to

A 
amplitude of 
the reflected 
signal or 
number of 
blood cells 
creating the 
reflection
105
Q

Pulsed doppler transducers: _ crystals, (dampened or undampened), _ Q factor, _ bandwidth, _ sensitivity

A

ateast one, dampened, low, wide, lower

106
Q

Continuous wave doppler transducers: _ crystals, (dampened or undampened), _ Q factor, _ bandwidth, _ sensitivity

A

atleast 2, undampened, high, narrow, higher

107
Q

Imaging vs doppler: Imaging: _ incidence, _ frequency, (pulsed or continuous wave), _ crystals

A

normal, higher, pulsed only, minimum of 1

108
Q

Imaging vs doppler: doppler: _ incidence, _ frequency, (pulsed or continuous wave), _ crystals

A

0 or 180 degrees, lower, pulsed or continuous, minimum of 1 (pulsed) or 2 (continuous)

109
Q

Color flow is a form of _

doppler

A

2D

110
Q

Color flow doppler: Velocity info is coded into _ and _

A

colors

superimposed on a 2D gray scale anatomic image.

111
Q

Color flow doppler is a _ ultrasound technique

A

pulsed

112
Q

Is color flow doppler subject to aliasing?

A

Yes

113
Q

Color flow doppler is associated with range _

A

resolution/specificity

114
Q

IS the angle between direction of sound and flow more or less important with color than with pulsed or continuous wave doppler?

A

less

115
Q

Color flow doppler reports _

A

average or mean velocities

116
Q

Pulsed and continuous wave doppler reports _

A

Peak velocities

117
Q

“Dictionary” used to convert
measured velocities into
colors that appear on the
image.

A

Color maps

118
Q

Color maps are used to convert _ into _

A

measured velocities

color

119
Q

Velocity mode: Colors provide information on

A

flow direction and velocity

120
Q

Black region in the middle of a color map indicates _

A

no doppler shift

121
Q

velocity mode: Colors above black line

indicate

A

flow towards

transducer

122
Q

Velocity mode: Colors below black line

indicate

A

flow away from

transducer

123
Q

Velocity mode: Color change

A

always up and down, never side to side

124
Q

Variance Mode: provides information on _

A

speed, direction, and distinguishes between turbulent and laminar flow

125
Q

Variance mode: colors on the left side indicate _

A

laminar

126
Q

Variance mode: colors on the right indicate _

A

turbulence

127
Q

With color Doppler, multiple ultrasound pulses are
used to accurately determine blood velocities
(called _)

A

a packet or ensemble

128
Q

Larger packets have two advantages:

A

More accurate velocity measurement

Increased sensitivity to low flow

129
Q

Disadvantages of larger packets:

A

More time needed to acquire data
Reduced frame rate
Decreased temporal resolution

130
Q

_ Only identifies presence of a

Doppler shif

A

power doppler

131
Q

Does power doppler evaluate speed or direction?

A

No

132
Q

Power doppler: All vessels have _

A

the same
color, regardless of the
direction of the blood flow

133
Q

Power doppler AKA

A

energy mode or

color angio

134
Q

Power doppler: Strength of reflected signal is processed (with or without) regard to the blood’s direction or speed.

A

without

135
Q

Advantages of power doppler

A

Increased sensitivity to low flow or velocity
Unaffected by Doppler angles, unless the angle is exactly 90°
No aliasing (velocity information is ignored)

136
Q

Disadvantages of power doppler

A

No measurement of velocity or direction
Lower frame rates (reduced temporal resolution)
Susceptible to motion of the transducer, patient, or
soft tissues, which may result in flash artifact

137
Q

Doppler shifts generally arise from

A

moving blood

138
Q

Slowly moving anatomy may also create

A

very low frequency doppler shifts

139
Q

low frequency Doppler shift

artifacts on a spectral display

A

Clutter

140
Q

low frequency

Doppler shift artifacts with color doppler

A

ghosting

141
Q

Clutter

A

low frequency Doppler shift

artifacts on a spectral display

142
Q

Ghosting

A

low frequency

Doppler shift artifacts with color doppler

143
Q

A _ is used to eliminate low frequency Doppler shifts from moving anatomy rather than moving blood cells

A

wall filter

144
Q

Wall filter serves as a _ for doppler

A

“reject”

145
Q

_wall filter eliminates _ but has no effect on _. Called _

A

low frequency doppler shifts around the baseline of a spectral display.
the higher frequency doppler shifts.
high pass filter

146
Q

With color, wall filters eliminate _

A

color arising from slow velocity reflectors.

147
Q

A special form of “mirror image” artifact that

arises only with spectral Doppler.

A

cross talk

148
Q

Crosstalk results from either:

A

Doppler gain is set too high
(electronic crosstalk)
or
The incident angle is near 90° between the sound beam and the flow direction, when flow is at the beam’s focus

149
Q

All blood cells within a sample volume (do or do not) travel at the same speed or direction.

A

do not

150
Q

_ is a 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

151
Q

Two methods of spectral analysis:

A

Fast Fourier Transform (FFT)

Autocorrelation

152
Q

A digital technique that is used to process both

pulsed and continuous wave Doppler signals

A

Fast Fourier

Transform

153
Q

_ is the process of separating a
waveform into a series of single-frequency sine-
wave components. When algebraically combined,
these components yield the original waveform

A

FFT

154
Q

2 advantages of FFT

A

Exceedingly accurate
Displays all individual velocity components that
make up the complex reflected signal.

155
Q

FFT distinguishes _

A

laminar from turbulent flow

156
Q

Fourier analysis is the process of _. When algebraically combined, these components _

A

separating a
waveform into a series of single-frequency sine-
wave components.
Yield the original waveform

157
Q

With laminar flow, most blood cells within the

sample volume travel at _ velocities

A

similar

158
Q

Spectral trace is a_ line

A

narrow, well defined

159
Q

FFT: Laminar flow: Region between the baseline and the

spectrum, called the _, is _

A

window

clear

160
Q

FFT: with turbulence, _ directions and speeds are within the sample volume

A

many different

161
Q

FFT: turbulence: pulsed soppler spectral window is _

A

filled in

162
Q

Spectral broadening

A

wider range of velocities and shifts in the sample volume

163
Q

spectral broadening can be caused by _

A

large gate

164
Q

Autocorrelation AKA

A

correlation function

165
Q

Digital technique used to analyze color flow

Doppler

A

Autocorrelation

166
Q

Is autocorrelation less accurate than FFT?

A

yes, somewhat

167
Q

Is autocorrelation faster than FFT?

A

Yes, substantially

168
Q

Autocorrelation is used with _ due to the enormous

amount of data that is processed.

A

color doppler

Physics (25 decks)

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