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Ultrasound Physics > Ch. 19/20 > Flashcards

Ch. 19/20 Flashcards

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1
Q

Doppler shift is also called ?

A

doppler frequency

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2
Q

When the sound source and receive move close together or far apart, what changes?

A

frequency of sound

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3
Q

A positive doppler shift means blood is moving ______ (from) the transducer. Which means the reflected frequency is higher or lower than transmitted frequency?

A

towards

higher frequency

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4
Q

A negative doppler shift means blood is moving _____ (from) the transducer. Which means the reflected frequency is higher or lower than transmitted frequency?

A

away

lower frequency

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5
Q

Doppler shift (Hz) = ________ subtracted from ________.

A

Reflected frequency subtracted from transmitted frequency

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6
Q

How is a doppler shift created?

A

when transmitted sound hits moving RBC’s.

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7
Q

What is doppler shift used for?

A

give us information about the
VELOCITY

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8
Q

What are the 2 things that indicate velocity?

A

magnitude and direction

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9
Q

What is the doppler shift equation?

A

Doppler shift = 2 x velocity of blood x transducer frequency x Cos divided by propagation speed

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10
Q

How is doppler shift related to propagation speed? directly or indirectly related?

A

indirectly

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11
Q

How is doppler shift related to velocity? directly or indirectly?

A

directly

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12
Q

How is doppler shift related to the frequency? directly or indirectly?

A

directly

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13
Q

How is doppler shift related to the cosine of the angle?

A

directly

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14
Q

Do the blood cells have to be parallel or perpendicular to the sound beam for the velocity to be measured 100% accurate?

A

parallel

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15
Q

When the angle is perpendicular to the sound beam, what happens to the doppler shift?

A

no doppler shift is detected, no velocity can be calculated

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16
Q

When the angle is in between parallel and perpendicular, can the velocity be measured?

A

yes, but it will be inaccurate since it will be above 60 degrees.

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17
Q

What degree of angle do we prefer when measuring velocity?

A

0 degrees

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18
Q

What degree of angles are ideal when measuring velocity that is going to get us close to the preferred angle?

A

between 0 and 60 degrees

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19
Q

What degree of angles should we avoid when measuring velocity?

A

anything above 60 degrees

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20
Q

What are the units for doppler shift?

A

Hz

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21
Q

Is there a positive or negative doppler shift ABOVE the baseline?

A

positive

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22
Q

Is there a positive or negative doppler shift BELOW the baseline?

A

negative

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23
Q

Doppler modalities include?

A

CW
PW
COLOR
POWER

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24
Q

A POSITIVE doppler shift indicates blood moving towards or away from the transducer?

A

towards

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25
A NEGATIVE doppler shift indicates blood moving towards or away from the transducer?
away
26
What is the advantage of using a CW doppler?
it accurately measures high velocities
27
What are the 2 disadvantages of using CW doppler?
-cannot determine the exact location of moving RBCs (called range ambiguity) -lacks time gain compensation 
28
How many crystals are used in a CW doppler transducer?
2 (one transmits, and one receives)
29
How many crystals do pulsed doppler transducers use?
one
30
Does a pulsed doppler transducer use damping material?
yes
31
Does a pulsed doppler transducer have a low or high Q-factor?
low
32
Does a pulsed doppler transducer have a wide or narrow bandwidth?
wide
33
Does a pulsed doppler transducer have low or high sensitivity?
low
34
Does a CW doppler transducer use damping material?
no
35
Does a CW doppler transducer have a high or low Q-factor?
High
36
Does a CW doppler transducer have a wide or narrow bandwidth?
narrow
37
Does a CW doppler transducer have high or low sensitivity?
high
38
What is the advantage of using a PW doppler?
able to select an exact location to measure velocity
39
What is the small marker used in a PW doppler to measure velocities called?
sample volume or gate
40
What is the disadvantage of using a PW doppler?
can inaccurately measure the height of the velocity signals. (Aliasing)
41
How are velocities calculated in PW doppler?
the frequency of returned signals corresponds to the depth of the sample volume
42
PRF determines what in PW doppler?
when the next sound waves are emitted
43
_____ (increased or decreased) depth requires _____ (increased or decreased) listening time and _____ (low or high) PRF.
increased depth increased listening time low PRF
44
What is PRF equal to?
Sample rate
45
How do you change the PRF?
by adjusting the depth
46
What is the formula for Nyquist limit?
Nyquist limit = PRF divided by 2.
47
What is the Nyquist limit?
The highest doppler frequency or velocity system can measure without aliasing.
48
Why does aliasing occur in a PW doppler?
when the doppler sample rate is too low in comparison to the velocities (Exceeds the speed limit)
49
How do you avoid aliasing?
-raise Nyquist limit -reduce the doppler shift (speed)
50
If you change the baseline, what happens to the Nyquist limit?
it is maintained
51
If you change the scale what happens to the Nyquist limit?
it increases or decreases
52
Less aliasing = _____ (slow or fast) velocity, _____ (high or low) frequency transducer and _____ (high or low) PRF
slow velocity low frequency high PRF
53
What does a color doppler do?
shows us the direction of flow at the average (mean) velocities
54
What does a spectral doppler (CW and PW) do?
measures the peak velocities
55
The top of the color map tells us that blood is moving (towards or away) from the transducer?
toward (positive doppler shift)
56
The bottom of the color map tells us that blood is moving (toward or away) from the transducer?
away (negative doppler shift)
57
If the blood is moving toward the probe, the frequency ______ (increases or decreases); if it's moving away, it _______ (increases or decreases)?
increases decreases (this is called doppler shift)
58
On the left side of a color map with solid red and blue means what kind of flow?
Laminar flow
59
On the right side of a color map with mixed colors (yellow, green, orange etc.) means what kind of flow?
Turbulent flow
60
Colors close to the black line indicate (fast or slow) velocities?
slow
61
Colors further from the black line indicate (fast or slow) velocities?
fast
62
What is variance mode?
distinguishes laminar flow from turbulent flow
63
What is a packet (ensemble)?
the number of ultrasound pulses transmitted along each scan line in color Doppler imaging
64
What is the advantage of large doppler packets?
accurately measure velocities and have increased sensitivity to low flow
65
What is the disadvantage of large doppler packets?
-more time required -reduces frame rate and temporal resolution
66
What is power doppler?
identifies the presence of a doppler shift by measuring amplitude, it cannot determine speed or direction
67
What are other names for power doppler?
energy mode or color angio
68
What are advantages of power doppler?
-increased sensitivity to low flow velocities (ideal for venous flow) -not affected by doppler angles -no aliasing
69
What are disadvantages of power doppler?
-no measurement of velocity or direction -reduced frame rate and temporal resolution -can cause flash artifacts from increased sensitivity to motion -
70
Does power doppler use many different colors?
no, only one color
71
Color doppler is best for (large or small) vessels? Power doppler is best for (large or small) vessels?
color doppler = large power doppler = small
72
What is ghosting?
-An artifact that occurs with color doppler. -Low-frequency doppler shifts cause color bleeding outside the vessel walls
73
What is clutter?
-An artifact that occurs in spectral Doppler imaging. -Low-frequency doppler shifts reduce the spectral window, making it harder to analyze blood flow accurately.
74
What is a wall filter used for?
help remove low-frequency signals that can cause artifacts like ghosting and clutter
75
What are two methods of spectral analysis?
-Fast Fourier Transform -Autocorrelation
76
Wall filters are also called?
High pass filters
77
What is FFT?
Associated with spectral Doppler -computer digital technique that is used to process PW and CW doppler signals.
78
What are advantages of FFT?
-Very accurate -Displays all individual velocities of complex reflected doppler signals
79
What does FFT help us distringush?
the spectral waveform between laminar and turbulent flow
80
What is autocorrelation?
Digital technique to analyze color flow doppler
81
How does autocorrelation differ from FFT?
-Faster than FFT -Less accurate than FFT
82
What is spectral broadening?
occurs with turbulent flow when the spectral window is completely filled in.

Ultrasound Physics (13 decks)

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