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Intro > Ch. 19 Doppler > Flashcards

Ch. 19 Doppler Flashcards

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1
Q

_________________________________ is the change in frequency of sound as the sound source and receiver move closer together or farther apart

A

Doppler Shift is the change in frequency of sound as the sound source and receiver move closer together or farther apart

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2
Q

Doppler Shift is also called Doppler _______________________

A

Doppler Shift is also called Doppler Frequency

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3
Q

Doppler Shift is a _____________ frequency that rides on top of the much higher transducer frequency

A

Doppler Shift is a low frequency that rides on top of the much higher transducer frequency

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4
Q

_________________________ is the process of extracting the low doppler frequency from the transducer’s carrier frequency

A

Demodulation is the process of extracting the low doppler frequency from the transducer’s carrier frequency

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5
Q

Short formula for Doppler Shift:

A

Doppler Shift (Hz) = reflected frequency - transmitted frequency

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6
Q

When the doppler shift is positive, the reflected sound has a __________________ frequency than the transmitted sound.

A

When the doppler shift is positive, the reflected sound has a higher frequency than the transmitted sound

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7
Q

When the doppler shift is negative, the reflected sound has a ____________________ frequency than the transmitted sound.

A

When the doppler shift is negative, the reflected sound has a lower frequency than the transmitted sound.

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8
Q

Doppler frequencies indicate _________________________, not speed.

A

Doppler frequencies indicate velocity, not speed

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9
Q

Speed is purely a ____________________________

A

Speed if purely a magnitude

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10
Q

Velocity is defined by a _______________ and a _________________

A

Velocity is defined by a magnitude and a direction

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11
Q

long formula for doppler shift:

A

Doppler Shift = 2 V Fo Cos / C

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12
Q

doppler shift is ____________________ related to the velocity of red blood cells

A

directly

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13
Q

The faster the velocity, the _____________________ the doppler shift

A

The faster the velocity, the greater the doppler shift

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14
Q

The x-axis of a doppler spectrum represents _______________

A

The x-axis of a doppler spectrum represents time

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15
Q

The y-axis of a doppler spectrum represents _________________________ or __________________________

A

The y-axis of a doppler spectrum represents Doppler shift or velocity

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16
Q

doppler shift is _________________ related to the frequency of the transmitted sound

A

doppler shift is directly related to the frequency of the transmitted sound

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17
Q

If the transducer frequency is doubled, the doppler shift will _______________

A

double

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18
Q

What is the range of frequencies for doppler shift?

A

20 Hertz - 20,000 Hertz (audiable range)

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19
Q

What is the relationship between the transmitted frequency and the doppler shift?

A

Directly related

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20
Q

When blood cells are moving __________ to the sound beam the entire velocity is measured

A

When blood cells are moving parallel to the sound beam the entire velocity is measured

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21
Q

The percentage of the true velocity that is measured depends on the ______________ of the angle between the sound beam and the direction of motion.

A

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

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22
Q

What information does doppler provide (4 things)?

A
  1. presence of flow
  2. direction of flow
  3. speed of flow
  4. characteristics of flow (laminar, turbulent)
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23
Q

cosine of 90 degrees

A

0%

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24
Q

cosine of 60 degrees

A

0.5 or 50%

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25
cosine of 0 degrees
100%
26
cosine of 180 degrees
- 1.0
27
The most common clinical doppler devices are _______________________________, which distinguish the direction of flow toward or away from the transducer
The most common clinical doppler devices are *Bidirectional*, which distinguish the direction of flow toward or away from the transducer
28
Are arterial velocities higher/lower than venous velocities
higher
29
Continuous wave doppler requires __________ crystals within the transducer
Continuous wave doppler requires *2* crystals within the transducer
30
What is the greatest advantage of continuous wave doppler?
Accurately measure very high velocities
31
Primary disadvantage of continuous wave doppler is?
The exact location of the moving blood cells cannot be determined
32
The limitation of continuous wave doppler is that the exact location of moving blood cells cannot be determined and this is called:
range ambiguity
33
Another disadvantage of continuous wave doppler is its lack of:
TGC's time gain compensation
34
A dedicated continuous wave transducer is simple because it does not create __________________________________
A dedicated continuous wave transducer is simple because it does not create *anatomic images*
35
Dedicated continuous wave transducers contain _____ elements, each shaped like a ___________________
Dedicated continuous wave transducers contain *2* elements, and each shaped like a *semicircle*
36
Simultaneous imaging and doppler imaging is called:
Duplex imaging
37
Dedicated continuous wave transducers do not use ______________________ which results in: - undampened transmitted signal - narrow bandwidth - high quality factor - higher sensitivity
Dedicated continuous wave transducers do not use *backing* which results in: - undampened transmitted signal - narrow bandwidth - high quality factor - higher sensitivity
38
In Pulsed wave doppler how many PZT crystals are necessary?
1
39
What is the greatest advantage of pulsed wave doppler?
the greatest advantage of pulsed wave doppler is being able to select the exact location where velocities are measured, called range resolution
40
The greatest advantage of pulsed wave doppler is called:
Range Resolution, Range Specificity, or freedom from range ambiguity artifact
41
With pulsed wave doppler the sonographer positions a small marker called the _______________________________________ on a 2D image
With pulsed wave doppler the sonographer positions a small marker called the *sample volume or sample gate* on a 2D image
42
What is the primary disadvantage of pulsed wave doppler?
Inaccurate measurement of high velocity signals
43
When high velocity flow is incorrectly displayed as traveling in the opposite direction the inaccuracy is called _______________________
When high velocity is incorrectly displayed as traveling in the opposite direction the inaccuracy is called *Aliasing*
44
Pulse wave doppler transducers are imaging transducers and contain _________________________________, which provide low Q-factor, lower sensitivity, and wide bandwidth pulses.
Pulse wave doppler transducers are imaging transducers and contain *backing material*, which provide low Q-factor, lower sensitivity, and wide bandwidth pulses.
45
_______________________ is the most common error associated with doppler ultrasound.
*Aliasing* is the most common error associated with doppler ultrasound
46
An alias is a:
false identity
47
Aliasing occurs only with __________________ doppler
Aliasing occurs only with *pulsed* doppler
48
Nyquist limit equation
Nyquist limit = PRF/2
49
______________________________ is the highest doppler frequency that can be measured without appearance of aliasing
*Nyquist limit* is the highest doppler frequency that can be measured without appearance of aliasing
50
2 ways to avoid aliasing are:
1. raise the nyquist limit 2. reduce the doppler shift
51
The sampling rate of pulsed doppler is the systems _____________
The sampling rate of pulsed doppler is the systems *PRF*
52
When sample volume is deep the PRF Is ___ and the nyquist limit is ___
low, low
53
Since deeper sample volumes have a lower PRF, __________ happens
Aliasing
54
Higher or Lower frequency transducers create more aliasing
Higher
55
5 techniques used to avoid aliasing artifact
1. adjust scale to max 2. select new ultrasonic view with shallower sample volume 3. select lower frequency transducers 4. use baseline shift 5. use continuous wave doppler
56
When the sonographer adjusts the scale to its max the ________________ is also increased to its max
When the sonographer adjusts the scale to its max the *PRF* is also increased to its max
57
What is the advantage of maximizing the PRF?
Maximizing the PRF, raises the nyquist limit and aliasing is less likely to occur
58
What is the disadvantage of raising the PRF to its max?
reduces sensitivity to low velocities
59
What is the advantage of selecting a lower frequency transducer?
lower shifts occur with lower frequency transducers
60
Advantage of zero baseline shift
High velocity flows are displayed in proper direction
61
Advantage of using continuous wave doppler
Aliasing never appears with continuous wave doppler
62
Eliminating aliasing improves the ability to measure the ____________________________ with doppler
Eliminating aliasing improves the ability to measure the *maximum velocity* with doppler
63
Gray shades on a Doppler spectrum are related to the ______________________ of reflected signal, or the number of ____________________________ creating the reflection.
Gray shades on a Doppler spectrum are related to the *amplitude* of reflected signal, or the number of *blood cells* creating the reflection.
64
_______________________________ is a form of 2D doppler where velocity information is coded into colors and superimposed on a 2 dimensional gray scale anatomic image
*Color Flow Doppler* is a form of 2D doppler where velocity information is coded into colors and superimposed on a 2 dimensional gray scale anatomic image
65
Color doppler provides information on the location of flow and therefore:
- is a pulsed ultrasound technique - has range resolution - is subject to aliasing
66
Color Doppler measures the ____ velocity.
Color Doppler measures the *mean* velocity
67
Spectral Doppler measures the _______________ velocity
Spectral Doppler measures the *peak* velocity
68
Color doppler uses a "dictionary" or a ___________________________ to concert measured velocities into colors that appear on the image
Color doppler uses a "dictionary" or a *lookup table* to concert measured velocities into colors that appear on the image
69
The two most commonly used dictionaries for color doppler are called:
Velocity mode and Variance mode
70
What do the colors mean in a velocity mode map mean?
Flow direction and velocity
71
What do the colors mean on a variance mode map?
In addition to direction and velocity, variance mode distinguishes laminar flow from turbulent flow
72
with the variance map, remember that the left side is always the __________________ side
with the variance map, remember that the left side is always the *laminar* side
73
The black region in the middle of the color map means?
No doppler shift
74
With color doppler multiple ultrasound pulses are used to accurately determine blood velocities, these multiple pulses are called a
packet or ensemble
75
Power mode only identifies the presence of a
Doppler shift
76
Power mode is _____________________ color doppler
Power mode is *non-directional* color doppler
77
Power Doppler is also known as:
~ energy mode ~ color angio
78
In power mode the ____________ of the reflected signal is processed without regard to the bloods direction or speed
In power mode the *strength* of the reflected signal is processed without regard to the bloods direction or speed
79
The amplitude of the reflection is _____________________ related to the number of moving blood cells
The amplitude of the reflection is *directly* related to the number of moving blood cells
80
3 advantages of power mode are:
1. Increased sensitivity 2. unaffected by doppler angles 3. no aliasing
81
3 disadvantages of power mode are:
1. no measurement of velocity or direction 2. lower frame rates 3. susceptible to motion of the transducer, patient, or soft tissues, which may result in a burst of color, or flash artifact
82
On spectral displays, the low frequency doppler shift artifacts are called _________________________
On spectral displays, the low frequency doppler shift artfiacts are called *clutter*
83
With color doppler, the low frequency doppler shifts are called ______________________________________
with color doppler, the low frequency doppler shifts are called *Ghosting Artifact*
84
What is used to eliminate low frequency doppler shifts from moving anatomy rather than from moving blood cells?
Wall filter
85
Wall Filters serve as a _____________________ for doppler
Wall Filters serve as a *Reject* for doppler
86
With color Doppler, _____________________ eliminate color arising from slow velocity reflectors
With color doppler, *wall filters* eliminate color arising from slow velocity reflectors
87
___________________________ is a special form of "mirror image" artifact that arises only with spectral doppler
*Crosstalk* is a special form of "mirror image" artfiact that arises only with spectral doppler
88
Crosstalk results from either:
1. Doppler gain is too high 2. incident angle is near 90°
89
_______________________________________ is a tool that breaks the complex signal into its basic "building blocks" and identifies the individual velocities that make up the reflected doppler signal.
*Spectral analysis* is a tool that breaks the complex signal into its basic "building blocks" and identifies the individual velocities that make up the reflected doppler signal
90
2 methods of spectral analysis are:
1. Fast Fourier Transform (FFT) 2. Autocorrelation
91
_____________________________________ is a digital (computer-based) technique that is used to process both pulsed and continuous wave doppler signals
*Fast Fourier Transformation* is a digital (computer-based) technique that is used to process both pulsed and continuous wave doppler signals
92
Fast Fourier Transformation has what 2 advantages?
1. exceedingly accurate 2. displays all individual velocities
93
The spectral display of an FFT distinguishes _______________________ flow from __________________________ flow
The spectral display of an FFT distinguishes *laminar flow* from *turbulent flow*
94
With laminar flow the region between the baseline and the spectrum that is "clear" and is called the
spectral window
95
With turbulence flow the spectral window is filled in and is known as
spectral broadening
96
The digital technique used to analyze color flow doppler is called ________________________________
The digital technique used to analyze color flow doppler is called *Autocorrelation*
97
Autocorrelation is somewhat less accurate but substantially faster to perform than ________________________________
Autocorrelation is somewhat less accurate but substantially faster to perform than *Fast Fourier Transformation*
98
The Doppler effect is presented as a ___________________ when the source and receiver are ________________
The Doppler effect is presented as a *frequency shift* when the source and receiver are *in motion relative to each other*
99
Starting from the same point, the sound source is moving toward the east at 12 miles/hour and the receiver is moving toward the west 10 miles/hour. The Doppler shift is ____________________ (positive or negative)
The Doppler shift is negative because the source and receiver are moving farther apart
100
Starting from the same point, the receiver is moving toward the west at 12 miles/hour and the source is moving toward the west at 10 miles/hour. The Doppler shift is _______________________ (positive or negative)
The Doppler shift is negative because the source and receiver are moving farther apart

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