Chapter 19 Flashcards
(168 cards)
1
Q
Doppler ultrasound can detect
_
A
The presence,
direction, velocity, and properties of blood
flow in vessels
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
3
Q
the change in frequency
between the transmitted frequency and the
received frequency
A
Doppler shift
4
Q
Doppler shifts are created when _
A
transmitted
sound waves strike moving red blood cells
5
Q
_ doppler shift: when blood cells
move toward the transducer; reflected
intensity is _ than the transmitted
frequency
A
positive
higher
6
Q
_ doppler shift: when blood cells
move away from the transducer; reflected
intensity is _ than the transmitted
frequency.
A
negative
lower
7
Q
If the transmitted frequency is higher than the reflected frequency,
what type of shift occurs?
A
negative
8
Q
If the reflected frequency is higher
than the transmitted frequency,
what type of shift occurs?
A
positive
9
Q
Doppler frequencies indicate _ not _
A
velocity
speed
10
Q
Speed or velocity:
Purely magnitude
A
speed
11
Q
Speed or velocity: Indicates the distance that a red blood cell
moves in 1 second
A
speed
12
Q
Speed or velocity: cm/s or other units of distance/time
A
speed
13
Q
Speed or velocity: Magnitude and direction
A
velocity
14
Q
The doppler equation
A
Doppler shift= (2 X velocity of blood X transducer frequency X cos) / propagation speed
15
Q
The two in the equation represents
A
that there
are actually two Doppler shifts during an
exam
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
17
Q
Relationship between doppler shift and velocity of RBC’s
A
direct
18
Q
The faster the velocity, the _ the doppler frequency
A
greater
19
Q
Modern ultrasound systems actually measure
A
the frequency difference (in hertz) between
received and transmitted waves
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
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
22
Q
Relationship between doppler shift and frequency of transmitted sound
A
direct
23
Q
If transducer’s frequency is doubled, the
measured Doppler shift will
A
also be doubled
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
25
When blood cells are moving parallel to the
| sound beam, the _ is measured
entire velocity
26
When an angle exists between the direction
of flow and the sound beam, the measured
velocity is _ than the true velocity
less
27
The percentage of the true velocity that is
| measured depends on
the cosine of the angle
between the sound beam and the direction of
motion.
28
Angle: 0
Cosine:
1.0
29
Angle: 30
Cosine:
0.87
30
Angle: 60
Cosine:
0.5
31
Angle: 90
Cosine:
0
32
Angle: 120
Cosine:
-0.5
33
Angle: 150
Cosine:
-0.87
34
Angle: 180
Cosine:
-1.0
35
Realtionship between doppler shift and cosine of the angle
direct
36
Relationship between doppler shift and the direction of sound
direct
37
If the cosine Θ is reduced by half, the
| measured Doppler shift will _
be halved
38
If flow is parallel to the sound beam, the angle between the direction of motion and sound is
0 degrees or 180 degrees
39
If flow is parallel to the sound beam, the measured and true velocities are _
equal
40
cosine 0 degrees is _, indicating flow _
1
| toward the transducer
41
cosine 180 degrees is _, indicating flow _
-1
| away from the transducer
42
If flow is perpendicular to the sound beam,
| the measured velocity is _. Cosine 90 degrees is _
zero
| zero
43
Doppler shifts and velocities cannot be
| measured with
perpendicular incidence
44
Most accurate measured velocity
Flow is parallel to the sound beam 0 degrees or 180 degrees
45
if blood moves at a 60° angle to the
| beam, the measured velocity is _ the actual velocity. Why?
1/2
| the cosine of 60 is 0.5
46
Bidirectional Doppler devices distinguish _
the
direction of flow toward or away from the
transducer.
47
A positive Doppler shift indicates flow _ the transducer
toward
48
A negative Doppler shift indicates flow _ the transducer
away from
49
Audio of bidirectional Doppler requires _
headphones or speakers, where sound from one
| speaker represents flow towards the transducer, and the other represents flow away from the transducer.
50
Flow toward the transducer is displayed _ the baseline
above
51
flow away from the
| transducer is displayed _ the baseline
below
52
Continuous Wave
| Doppler requires _ crystals
2
53
In continuous wave trandsucers, one crystal _ while the other _
constantly transmits
continuously receives
reflections from blood cells
54
Greatest advantage of continuous wave doppler is its ability to _
accurately measure very high velocities.
55
Disadvantages of continuous wave doppler
range ambiguity
| Lack of TGC
56
Range ambiguity
Exact location of the moving blood cells
| cannot be determined
57
Do continuous wave transducers use backing material?
No
58
Do continuous wave transducers have a matching layer?
Yes
59
In pulsed wave Doppler, _ PZT crystal is
| necessary.
only one
60
With pulsed wave doppler, sonographers position _. The US system calculates _
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.
61
Advantage of pulsed wave doppler:
the ability to select the exact location where velocities are measured.
62
AKA range resolution, range specificity, or
| freedom from range ambiguity artifact.
the ability to select the exact location where velocities are measured
63
Disadvantages of pulsed wave doppler
Inaccurate measurement of high velocity
signals.
High velocity flow in one direction is incorrectly
displayed as traveling in the opposite direction.
64
High velocity flow in one direction is incorrectly
| displayed as traveling in the opposite direction.
Aliasing
65
Studies that simultaneously perform imaging
| and pulsed Doppler are called
duplex exams
66
pulsed wave transducers: _ crystals, contains _, _ Q factor, _ sensitivity, _ bandwith
```
single
backing material
low
low
wide
```
67
Most common error associated with Doppler
| ultrasound.
Aliasing
68
Aliasing
Very high velocities in one direction are
incorrectly displayed as going in the opposite
direction.
69
```
Velocity of blood cells reach
the very top of the spectral
display and incorrectly
wrap around and appear at
the bottom of the display
```
Aliasing
70
The very top or bottom of the display
nyquist limit
71
Can aliasing occur in the opposite direction?
Yes
72
Aliasing only occurs with _ doppler
pulsed
73
Aliasing occurs when doppler sampling rate is _
too low in comparison to the measured blood
| velocities
74
Nyquist limit = _ PRF
1/2
75
Nyquist limit = _
PRF/2
76
Two ways to avoid aliasing:
Raise the Nyquist limit
| Reduce the Doppler shift
77
When the sample volume is deep, the
| PRF is _ and the nyquist limit is _. This can create _
low
low
aliasing
78
When the sample volume is shallow,
| the PRF is_ and the nyquist limit is _. The system
high
high
accurately measures
high velocity without aliasing.
79
_ frequency transducers create more
| aliasing.
higher
80
Relationship between doppler shift and transducer frequency
directly
81
At a particular velocity, higher frequency
| transducers create _ doppler shifts and lower frequency transducers create _doppler shifts
higher
| lower
82
Aliasing artifacts are less common with _ frequency transducers due to _
lower
the Doppler
shifts being less likely to exceed the Nyquist
limit.
83
Less aliasing: _ velocity, _ frequency transducer, _ gate, _ PRF
slower, lower, shallow, higher
84
More alaiasing: _ velocity, _ frequency, _ gate, _ PRF
faster, higher, deep, low
85
Five techniques may be used to avoid
| aliasing artifact:
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
Advanages of adjusting scale to its maximum
raises the nyquist limit and aliasing
| is less likely to appear
87
Disadvantages of adjusting scale to its maximum
higher PRF reduces sensitivity to low velocities.
With very high velocities, aliasing artifact persists,
even when the scale is maximized.
88
If the scale is adjusted to its maximum, the PRF is _
also adjusted to its
| maximum. (increase PRF increases Nyquist limit)
89
Advantages of selecting a new ultrasonic view with a shallower sample volume
PRF is increased, Nyquist limit increased,
| aliasing is reduced
90
Disadvantages of selecting a new ultrasonic view with a shallower sample volume
None
91
Advantages of selecting a lower frequency transducer
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
Disadvantages of selecting a lower frequency transducer
No significant disadvantages other than producing
| a lower quality anatomic image
93
Baseline usually appears _
in the middle of the display
94
_ simply slides the display baseline up or down so
| that the entire velocity scale is devoted to one direction.
Baseline shift
95
Advantages of baseline shift
High velocity flows are displayed in the proper direction.
| Measurements remain accurate even after shifting the baseline
96
Disadvantages of baseline shift
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
Advantages of continuous wave doppler
Aliasing never appears
| with continuous wave Doppler.
98
Disadvantages of continuous wave doppler
```
Range ambiguity
Velocities along the entire region of
overlap between the transmit and receive
beams blend together to form the
spectrum
```
99
Techniques that eliminated aliasing:
Method: Adjust scale
Strategy: _
Increase nyquist limit
100
Techniques that eliminated aliasing:
Method: new, shallower view
Strategy: _
increase nyquist limit
101
Techniques that eliminated aliasing:
Method: lower transducer frequency
Strategy: _
decrease doppler shift
102
Techniques that eliminated aliasing:
Method: zero baseline shift
Strategy: _
aliasing remains but display is more appealing
103
Techniques that eliminated aliasing:
Method: Continuous wave doppler
Strategy: _
never aliases, but range ambiguity
104
Gray shades
on a doppler
spectrum are
related to
```
amplitude of
the reflected
signal or
number of
blood cells
creating the
reflection
```
105
Pulsed doppler transducers: _ crystals, (dampened or undampened), _ Q factor, _ bandwidth, _ sensitivity
ateast one, dampened, low, wide, lower
106
Continuous wave doppler transducers: _ crystals, (dampened or undampened), _ Q factor, _ bandwidth, _ sensitivity
atleast 2, undampened, high, narrow, higher
107
Imaging vs doppler: Imaging: _ incidence, _ frequency, (pulsed or continuous wave), _ crystals
normal, higher, pulsed only, minimum of 1
108
Imaging vs doppler: doppler: _ incidence, _ frequency, (pulsed or continuous wave), _ crystals
0 or 180 degrees, lower, pulsed or continuous, minimum of 1 (pulsed) or 2 (continuous)
109
Color flow is a form of _
| doppler
2D
110
Color flow doppler: Velocity info is coded into _ and _
colors
| superimposed on a 2D gray scale anatomic image.
111
Color flow doppler is a _ ultrasound technique
pulsed
112
Is color flow doppler subject to aliasing?
Yes
113
Color flow doppler is associated with range _
resolution/specificity
114
IS the angle between direction of sound and flow more or less important with color than with pulsed or continuous wave doppler?
less
115
Color flow doppler reports _
average or mean velocities
116
Pulsed and continuous wave doppler reports _
Peak velocities
117
“Dictionary” used to convert
measured velocities into
colors that appear on the
image.
Color maps
118
Color maps are used to convert _ into _
measured velocities
| color
119
Velocity mode: Colors provide information on
flow direction and velocity
120
Black region in the middle of a color map indicates _
no doppler shift
121
velocity mode: Colors above black line
| indicate
flow towards
| transducer
122
Velocity mode: Colors below black line
| indicate
flow away from
| transducer
123
Velocity mode: Color change
always up and down, never side to side
124
Variance Mode: provides information on _
speed, direction, and distinguishes between turbulent and laminar flow
125
Variance mode: colors on the left side indicate _
laminar
126
Variance mode: colors on the right indicate _
turbulence
127
With color Doppler, multiple ultrasound pulses are
used to accurately determine blood velocities
(called _)
a packet or ensemble
128
Larger packets have two advantages:
More accurate velocity measurement
| Increased sensitivity to low flow
129
Disadvantages of larger packets:
More time needed to acquire data
Reduced frame rate
Decreased temporal resolution
130
_ Only identifies presence of a
| Doppler shif
power doppler
131
Does power doppler evaluate speed or direction?
No
132
Power doppler: All vessels have _
the same
color, regardless of the
direction of the blood flow
133
Power doppler AKA
energy mode or
| color angio
134
Power doppler: Strength of reflected signal is processed _(with or without)_ regard to the blood’s direction or speed.
without
135
Advantages of power doppler
Increased sensitivity to low flow or velocity
Unaffected by Doppler angles, unless the angle is exactly 90°
No aliasing (velocity information is ignored)
136
Disadvantages of power doppler
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
Doppler shifts generally arise from
moving blood
138
Slowly moving anatomy may also create
very low frequency doppler shifts
139
low frequency Doppler shift
| artifacts on a spectral display
Clutter
140
low frequency
| Doppler shift artifacts with color doppler
ghosting
141
Clutter
low frequency Doppler shift
| artifacts on a spectral display
142
Ghosting
low frequency
| Doppler shift artifacts with color doppler
143
A _ is used to eliminate low frequency Doppler shifts from moving anatomy rather than moving blood cells
wall filter
144
Wall filter serves as a _ for doppler
"reject"
145
_wall filter eliminates _ but has no effect on _. Called _
low frequency doppler shifts around the baseline of a spectral display.
the higher frequency doppler shifts.
high pass filter
146
With color, wall filters eliminate _
color arising from slow velocity reflectors.
147
A special form of “mirror image” artifact that
| arises only with spectral Doppler.
cross talk
148
Crosstalk results from either:
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
All blood cells within a sample volume _(do or do not)_ travel at the same speed or direction.
do not
150
_ is a tool that breaks the
complex signal into basic building blocks and
identifies the individual velocities that make
up the reflected Doppler signal
Spectral analysis
151
Two methods of spectral analysis:
Fast Fourier Transform (FFT)
| Autocorrelation
152
A digital technique that is used to process both
| pulsed and continuous wave Doppler signals
Fast Fourier
| Transform
153
_ 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
FFT
154
2 advantages of FFT
Exceedingly accurate
Displays all individual velocity components that
make up the complex reflected signal.
155
FFT distinguishes _
laminar from turbulent flow
156
Fourier analysis is the process of _. When algebraically combined, these components _
separating a
waveform into a series of single-frequency sine-
wave components.
Yield the original waveform
157
With laminar flow, most blood cells within the
| sample volume travel at _ velocities
similar
158
Spectral trace is a_ line
narrow, well defined
159
FFT: Laminar flow: Region between the baseline and the
| spectrum, called the _, is _
window
| clear
160
FFT: with turbulence, _ directions and speeds are within the sample volume
many different
161
FFT: turbulence: pulsed soppler spectral window is _
filled in
162
Spectral broadening
wider range of velocities and shifts in the sample volume
163
spectral broadening can be caused by _
large gate
164
Autocorrelation AKA
correlation function
165
Digital technique used to analyze color flow
| Doppler
Autocorrelation
166
Is autocorrelation less accurate than FFT?
yes, somewhat
167
Is autocorrelation faster than FFT?
Yes, substantially
168
Autocorrelation is used with _ due to the enormous
| amount of data that is processed.
color doppler
