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Physics CT > Doppler > Flashcards

Doppler Flashcards

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1
Q

what is the doppler effect?

A

the change in frequency or wavelength of echo signals that occurs when there is relative motion between the transducer (sound source) and reflecting surfaces (red blood cells)

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2
Q

flow toward the transducer is?

A

a positive doppler shift

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3
Q

flow away from the transducer is?

A

a negative doppler shift

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4
Q

what is the difference between the recieved and transmitted frequencies?

A

the doppler shift

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5
Q

what units are used to express doppler shift?

A

kilohertz or kHZ

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6
Q

the frequency transmittes by the transducer can also be referred to as?

A

transmitted frequency
emitted frequency
incident frequency
operating frequency

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7
Q

transmitted frequency and the change in frequency are inverslely related
true/false

A

false
they are directly related

ex: if the transmitted frequency is doubled, then the change in frequency is doubled.

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8
Q

where is the cosine of the angle measured?

A

between the direction of blood flow and the axis of the beam.

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9
Q

what are the cosines for the following angles?

0°
60°
90°

A

1
.5
0

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10
Q

what factors influence the magnitude of the doppler shift frequency?

A

range of the doppler shift frequencies
effects of beam angle
transmitted frequency

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11
Q

if the RBC’s are moving toward the transducer, what waveforms are displayed?

A

a positive doppler shift

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12
Q

if RBC’s are moving away from the transducer, what waveforms are displayed?

A

a negative doppler shift

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13
Q

if you have a faster flow velocity, you will have a higher doppler shift.
true/fasle

A

true

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14
Q

how many crystals does a CW probe use?

A

2

one sends & one receives

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15
Q

what are the advantages for CW?

A

ability to measure high velocities
no aliasing
small probe sizes
ability to use high frequencies

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16
Q

what is the biggest disadvantage for CW?

A

range ambiguity; inability to determine where the doppler signal is coming from

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17
Q

how many crystals are used for PW?

A

1

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18
Q

the term applied when only the information from the selected gate will be processed is?

A

range resolution

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19
Q

what is the nyquist limit? what is the formula?

A

the level at which aliasing will begin to occur

1/2PRF

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20
Q

aliasing occurs as the bottom of the spectrum wrapping around into the opposite half of the baseline
true/false

A

false

it is the top of the spectrum

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21
Q

what are ways to correct aliasing?

A
  • properly adjusting the spectral baseline &/or spectral scale
  • try a different window that gives a shallower depth
  • using a lower frequency transducer
22
Q

what is an advantage of PW doppler?

A

range resolution

23
Q

in spectral analysis, what is displayed on the horizontal axis?

A

time

24
Q

in spectral analysis, what is displayed on the vertical axis?

A

frequency shift or velocity

25
Q

a poitive doppler shift is below the baseline?

true/false

A

false; it is above the baseline.

26
Q

wave form brightness is also known as what?

A

the amplitude of the signal

27
Q

what does FFT stand for?

A

fast fourier transformer

28
Q

what is FFT?

A

a device that converts the doppler shift info into the visual spectral analysis

29
Q

FFT breaks down these complex signals into each individual frequency
true/false

A

true

30
Q

what is the range of packets per line of color?

A

3 to 30 pulses

31
Q

what is the number of pulses sent per line of color refered to as?

A

packet size or ensemble length

32
Q

for the color map, the top color is assigned to all velocities flowing in which direction?

A

toward the transducer

33
Q

for the color map, the bottom color is assigned to all velocities flowing in which direction?

A

away from the transducer

34
Q

faster velocities are represented by darker colors or hues

true/false

A

false; they are represented by ligher colors

35
Q

what is saturation?

A

the degree to which the original color is diluted with white

36
Q

the deeper the color, i.e. deep red or blue, represent faster flow
true/false

A

false; faster colors are represented by lighter hues

37
Q

color doppler is angle dependent

true/false

A

true

38
Q

what is triplex imaging consist of?

A

b-mode
color doppler
pulse wave doppler

39
Q

what is the disadvantage of color doppler?

A

aliasing

40
Q

where in a vessel are you likely to see aliasing?

A

after stenosis

41
Q

what is autocorrelation?

A

a technique used to rapidly obtain doppler shift frequencies used in color flow doppler

42
Q

autocorrelation has a decreased frame rate, which decreases which resolution?

A

temporal

43
Q

power doppler is angle dependent

true/false

A

false; power doppler is not angle dependent

44
Q

the most inaccurate doppler shift occurs when the angle is

A

90°

45
Q

as the angle between the transducer and flow decreses, the doppler shift:

A

increases

46
Q

noise in the doppler signal that is generally cause by high amplitude, doppler shifted echoes is called:

A

clutter

47
Q

the wall filter used in doppler is a type of?

A

reject control

48
Q

a faster but less accurate signal process used in color flow doppler is called?

A

autocorrelation

49
Q

signal processing of the doppler signal is accomplished by the?

A

fast fourier transform (FFT)

50
Q

color power/energy mode is also known as

A

color angio or power doppler

Physics CT (2 decks)

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