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Physics 3 > Doppler > Flashcards

Doppler Flashcards

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1
Q

What is the transducer used in doppler

A

The same as 2D and all doppler applications

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2
Q

What is the different about doppler frequency

A

Lower than the frequency for 2D images

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3
Q

Why is the frequency different for doppler than 2D images

A

It accounts for the attenuation from the RBC’s

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4
Q

How many pulses per cycle will the pulser generate for doppler to improve the accuracy

A

5-30

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5
Q

What is the doppler shift detection typically the result of

A

Quadratics phase detection

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6
Q

What is the quadratic phase detector

A

The transmitted signal is duplicated and stored

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7
Q

What is another name for the transmitted signal

A

Reference signal

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8
Q

The reference signals are the same except for what

A

They are 1/4 out of phase with each other

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9
Q

What is the returning signal compared to and why

A

The reference signal, to determine a positive or negative shift

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10
Q

What can the result signal be sent to for image processing

A

Loudspeaker

Spectral analyzer

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11
Q

Is the doppler shifted signal complex or simple

A

Complex

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12
Q

What does the doppler shifted signal contain

A

All the shifts that occur in the sample gate

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13
Q

The spectrum analyzer is a means of what

A

Separating the individual doppler shifts from the complex beat frequency

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14
Q

The spectrum analyzer is synonymous to what

A

A prism separating the different hues that comprise white light

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15
Q

Doppler signals are separated into what

A

Doppler shifted frequencies

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16
Q

What is the process that separates the doppler signals

A

Fast Fourier transformation (FFT)

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17
Q

What does the FFT analyze

A

The complex doppler shift signal

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18
Q

What does the FFT break the shifted doppler signal into

A

It’s component or separate frequencies, displaying both magnitude and amplitude

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19
Q

Depending of the speed of the processor, how many spectra can the FFT produce per second

A

100-1000

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20
Q

The separate doppler shifts are plotted on what

A

The y-axis over time

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21
Q

The magnitude of the doppler shift is

A

The amount of positive and negative shift

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22
Q

+4 kHz doppler shift is the same magnitude as what

A

A -4kHz

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23
Q

What are the factors effecting magnitude

A

RBC velocity
Angle of insonation
Operating frequency

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24
Q

The amplitude of the doppler shift represents what

A

The number of RBC’s that are contained within the sample volume

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25
Q

Amplitude of the doppler signal is also

A

How bright the signal is

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26
Q

Two 4 kHz doppler shifts have the same magnitude but may not have the same what

A

Amplitude

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27
Q

What are the factors effecting amplitude

A

RBC density
Attenuation
Power
Gain

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28
Q

What is the sample volume comprised of

A

Beam width
Gate length
Pulse length

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29
Q

What is another consideration about the sample volume of PW doppler

A

That it is actually a three-dimensional volume that changes in size relative to depth

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30
Q

What happens to the sample volume when it is placed in the far field

A

It becomes very large

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31
Q

Why does aliasing occur

A

Pulsed doppler is a sampling system and it is possible that the velocities of the RBC’s will exceed the sampling limit of the machine

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32
Q

What limits the amount of sampling

A

Depth

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33
Q

Aliasing occurs when

A

The nyquist limit is exceeded

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34
Q

What is the formula for the nyquist limit

A

Nyquist limit= 1/2 PRF

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35
Q

What are the 5 ways to correct for aliasing

A 
Change the baseline 
Increase the PRF 
Lower the frequency 
Increase the doppler angle 
Switch to CW
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36
Q

What are the only two practical ways to correct for aliasing in a clinical setting

A

Change the baseline

Increase the PRF

37
Q

If there is lots of aliasing occuring in an echo what is a good solution

A

Switching to a CW probe

38
Q

Some machines are capable of what

A

Operating in high PRf mode when the velocities exceed the nyquist limit

39
Q

What does operating in high PRF mode allow the machine to do

A

Fire the next pulse before all the echoes from the first pulse have returned

40
Q

What can operating in a high PRF help raise and what is the down fall

A

The nyquist limit, the downfall is the consequence of possible range ambiguity

41
Q

In high PRF mode what is possible

A

To pick up flow from more than one depth

42
Q

What could the resultant spectral tracing be when using high PRF mode

A

Very complex, displaying the flow profiles of multiple vessels

43
Q

The sweep speed of the spectral trace can be what

A

Altered to accommodate different types of measurements

44
Q

Fast sweeps are used for ____ and why

A

Intracycle measurements, due to the easier caliber placement and increased accuracy for systolic events

45
Q

Slow sweeps are more for what

A

Intercycle measurements

46
Q

What are examples of intercycle measurements

A

Rate

Rhythm

47
Q

CW works similar to

A

Pulsed doppler

48
Q

CW has what

A

An oscillator that produces a continuous AC voltage for motion detection

49
Q

The echo can be sent to what

A

A speaker or processed into an image

50
Q

Doppler is sensitive to what

A

Any motion, not just moving RBC’s

51
Q

What is the function of the wall filter

A

It reject the low frequencies from wall motion of pulsatile vessels

52
Q

What is the trade off of using a wall filter

A

If set too high, it can reject real blood velocities in the lower frequency range

53
Q

Colour doppler provides a complete what

A

Qualitative blood flow analysis over a wide field of view

54
Q

What does colour doppler combine

A

Anatomical detail from the 2D image and physiological hemodynamics with the colour overlay

55
Q

What are the synonyms for colour doppler

A

Colour doppler imaging
Colour flow imaging
Colour flow mapping
Colour doppler

56
Q

How many processes are required to display colour doppler

A

2

57
Q

What are the 2 processes required for colour doppler

A

Standard 2D processing

Doppler processing

58
Q

What do these processes mean

A

Several pulses per scan line are required, which has a huge impact on the frame rate

59
Q

What is the technique called for processing colour doppler

A

Autocorrelation

60
Q

What is autocorrelation

A

The mathematical means of rapidly determining the sign, mean, power and variance of the returning signal

61
Q

How many doppler samples are typically displayed per scan line

A

100-400

62
Q

What are the frames rates of 5-50 hZ typically dependant on

A

The depth and size of the field of view

63
Q

What is another name for ensemble length

A

Packet size

64
Q

What is ensemble length

A

The number of pulses used for each colour scan line

65
Q

The colour data represents what

A

A mean or average of the velocities present

66
Q

To calculate a mean velocity what is the minimum amount of pulses required

A

3

67
Q

How many pulses are commonly used to calculate a mean velocity

A

10-20

68
Q

What does a longer ensemble length mean

A

Slower frame rate

69
Q

What information does autocorrelation yield about the blood flow

A

Sign
Magnitude
Power
Variance

70
Q

What is another term for sign

A

Hue

71
Q

What is another term for magnitude

A

Saturation

72
Q

What is another term for power

A

Luminance

73
Q

What is the hue

A

The colour that you see

74
Q

What does hue represent

A

The sign or direction of flow

75
Q

Saturation is

A

The amount of colour in a mix with whiter

76
Q

What does saturation represent

A

The magnitude of the doppler shift or how fast the blood is travelling

77
Q

If more white is present what dies that mean

A

There is less saturation and faster flow

78
Q

Luminance is

A

The brightness of the hue and saturation presented

79
Q

Luminance represents what

A

The power of the flow and tells us the RBC density within the field of view

80
Q

More RBC’s travelling at the same velocity in a sample will appear what on the display

A

Brighter

81
Q

Variance displays what

A

The amount of velocities that different than the mean

82
Q

A variance map can give greater detail then what

A

The averaged velocities in a hue or saturation map

83
Q

What is another colour doppler control called that determines whether or not the colour overlay will overwrite low level echoes

A

Priority

84
Q

If priority is set low then what happens

A

Precedence is given to non-doppler-shifted weak echoes

85
Q

What does a high priority allow for

A

The colour to overwrite the low 2D echoes

86
Q

What is power doppler also know as

A

Energy mode

87
Q

What does the colour displayed in power doppler represent and as opposed to what

A

The strength of the doppler shift, opposed to the velocity

88
Q

Power doppler is

A

Free of aliasing
Less dependant on angle
Very sensitive to low flow states

89
Q

What is the downside of power doppler

A

No direction
Flow speed
Character information
Very susceptible to blooming artifacts

Physics 3 (5 decks)

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