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Physics 3 > Doppler > Flashcards

Doppler Flashcards

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
Amplitude of the doppler signal is also
How bright the signal is
26
Two 4 kHz doppler shifts have the same magnitude but may not have the same what
Amplitude
27
What are the factors effecting amplitude
RBC density Attenuation Power Gain
28
What is the sample volume comprised of
Beam width Gate length Pulse length
29
What is another consideration about the sample volume of PW doppler
That it is actually a three-dimensional volume that changes in size relative to depth
30
What happens to the sample volume when it is placed in the far field
It becomes very large
31
Why does aliasing occur
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
32
What limits the amount of sampling
Depth
33
Aliasing occurs when
The nyquist limit is exceeded
34
What is the formula for the nyquist limit
Nyquist limit= 1/2 PRF
35
What are the 5 ways to correct for aliasing
``` Change the baseline Increase the PRF Lower the frequency Increase the doppler angle Switch to CW ```
36
What are the only two practical ways to correct for aliasing in a clinical setting
Change the baseline | Increase the PRF
37
If there is lots of aliasing occuring in an echo what is a good solution
Switching to a CW probe
38
Some machines are capable of what
Operating in high PRf mode when the velocities exceed the nyquist limit
39
What does operating in high PRF mode allow the machine to do
Fire the next pulse before all the echoes from the first pulse have returned
40
What can operating in a high PRF help raise and what is the down fall
The nyquist limit, the downfall is the consequence of possible range ambiguity
41
In high PRF mode what is possible
To pick up flow from more than one depth
42
What could the resultant spectral tracing be when using high PRF mode
Very complex, displaying the flow profiles of multiple vessels
43
The sweep speed of the spectral trace can be what
Altered to accommodate different types of measurements
44
Fast sweeps are used for ____ and why
Intracycle measurements, due to the easier caliber placement and increased accuracy for systolic events
45
Slow sweeps are more for what
Intercycle measurements
46
What are examples of intercycle measurements
Rate | Rhythm
47
CW works similar to
Pulsed doppler
48
CW has what
An oscillator that produces a continuous AC voltage for motion detection
49
The echo can be sent to what
A speaker or processed into an image
50
Doppler is sensitive to what
Any motion, not just moving RBC’s
51
What is the function of the wall filter
It reject the low frequencies from wall motion of pulsatile vessels
52
What is the trade off of using a wall filter
If set too high, it can reject real blood velocities in the lower frequency range
53
Colour doppler provides a complete what
Qualitative blood flow analysis over a wide field of view
54
What does colour doppler combine
Anatomical detail from the 2D image and physiological hemodynamics with the colour overlay
55
What are the synonyms for colour doppler
Colour doppler imaging Colour flow imaging Colour flow mapping Colour doppler
56
How many processes are required to display colour doppler
2
57
What are the 2 processes required for colour doppler
Standard 2D processing | Doppler processing
58
What do these processes mean
Several pulses per scan line are required, which has a huge impact on the frame rate
59
What is the technique called for processing colour doppler
Autocorrelation
60
What is autocorrelation
The mathematical means of rapidly determining the sign, mean, power and variance of the returning signal
61
How many doppler samples are typically displayed per scan line
100-400
62
What are the frames rates of 5-50 hZ typically dependant on
The depth and size of the field of view
63
What is another name for ensemble length
Packet size
64
What is ensemble length
The number of pulses used for each colour scan line
65
The colour data represents what
A mean or average of the velocities present
66
To calculate a mean velocity what is the minimum amount of pulses required
3
67
How many pulses are commonly used to calculate a mean velocity
10-20
68
What does a longer ensemble length mean
Slower frame rate
69
What information does autocorrelation yield about the blood flow
Sign Magnitude Power Variance
70
What is another term for sign
Hue
71
What is another term for magnitude
Saturation
72
What is another term for power
Luminance
73
What is the hue
The colour that you see
74
What does hue represent
The sign or direction of flow
75
Saturation is
The amount of colour in a mix with whiter
76
What does saturation represent
The magnitude of the doppler shift or how fast the blood is travelling
77
If more white is present what dies that mean
There is less saturation and faster flow
78
Luminance is
The brightness of the hue and saturation presented
79
Luminance represents what
The power of the flow and tells us the RBC density within the field of view
80
More RBC’s travelling at the same velocity in a sample will appear what on the display
Brighter
81
Variance displays what
The amount of velocities that different than the mean
82
A variance map can give greater detail then what
The averaged velocities in a hue or saturation map
83
What is another colour doppler control called that determines whether or not the colour overlay will overwrite low level echoes
Priority
84
If priority is set low then what happens
Precedence is given to non-doppler-shifted weak echoes
85
What does a high priority allow for
The colour to overwrite the low 2D echoes
86
What is power doppler also know as
Energy mode
87
What does the colour displayed in power doppler represent and as opposed to what
The strength of the doppler shift, opposed to the velocity
88
Power doppler is
Free of aliasing Less dependant on angle Very sensitive to low flow states
89
What is the downside of power doppler
No direction Flow speed Character information Very susceptible to blooming artifacts

Physics 3 (5 decks)

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