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Phys 314 Physics 3 > Doppler > Flashcards

Doppler Flashcards

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1
Q

Label

A
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2
Q

In terms of doppler instrumentation, the transducer is the same for what?

A

Same for 2D and all doppler applications

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3
Q

The frequency for doppler is lower than what? Why?

A

The frequency is lower than the frequency of the 2D images to account for the attenuation from the RBCs

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4
Q

In terms of doppler instrumentation, the pulse will generate 5-30 cycles pulses why?

A

For doppler to improve accuracy

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5
Q

The doppler shift detection is typically the result of what?

A

Quadrature phase detector where the transmitted signal (Reference signal) is duplicated and stored

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6
Q

In terms quadrature phase detector, the reference signals are same except what?

A

They are 1/4 out of phase with each other

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7
Q

In terms of quadrature phase detector, the returning signal is compared to what?

A

The reference signal to determine a positive or negative shift

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8
Q

In terms of quadrature phase detector, The resultant signal can be sent to what?

A

A loudspeaker or a spectral analyzer for imaging processing

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9
Q

What does this image represent?

A

Quadrature phase detector

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10
Q

The doppler shifted signal is complex and contains what?

A

All of the shifts that occur in the sample gate

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11
Q

In terms of doppler, the spectrum analyzer is a means of what? This is synonymous to what?

A
  1. Separating the individual doppler shifts form the complex beat frequency
  2. A prism separating the different hues that comprise white light
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12
Q

Doppler signals are separated into what? Through what technique?

A

Doppler shifted frequencies through the process of FFT (Fast Fourier transform)

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13
Q

FFT analyzes the complex doppler shift signal and does what?

A

Breaks the signal into its component or separate frequencies displaying both magnitudes and amplitude

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14
Q

In terms of FFT, depending on the speed of the processeor, FFT can produce what?

A

100-1000 spectra per second

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15
Q

In terms of FFT, the separate doppler shifts are plotted where?

A

On the Y axis over time

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16
Q

What does this image represent?

A

FFT with doppler shift

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17
Q

The magnitude of the doppler shift is the amount of what?

A

Positive or negative shift

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18
Q

+4kHz doppler shift is the same magnitude as what?

A

a -4kHz
The magnitudes are equal but the sign is opposite

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19
Q

Factors effecting magnitude are what? 3

A
  1. RBC velocity
  2. Angle of insonation
  3. Operating frequency
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20
Q

The amplitude (brightness) of the doppler shift represents what?

A

The number of RBCs that are contained within the sample volume

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21
Q

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

A

The same amplitude

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22
Q

Sample volume is comprised of what? 3

A
  1. Beam width
  2. Gate length
  3. The pulse length
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23
Q

The sample volume of PW is actually what?

A

A 3D volume that changes in size relative to depth

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24
Q

When the sample volume is placed in the far field, what happens?

A

It becomes very large

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25
Q

Aliasing occurs because of what?

A

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

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26
Q

Aliasing occurs when what is exceeded?

A

Nyquist limit

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27
Q

What is the Nyquist limit?

A

(1/2) PRF

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28
Q

What are the 5 ways to correct for aliasing. What are they? And what are the most practical in clinical?

A
  1. Change the baseline
  2. Increase the PRF
  3. Lower the frequency
  4. Increase the doppler angle
  5. Switch to CW
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29
Q

What is a good way to get rid of aliasing in echo?

A

Continuous wave

30
Q

What limits the amount of sampling?

A

Depth

(Depth decreases PRF)

31
Q

Some machines are capable of operating in the high PRF mode when what happen? This exceeds what the Nyquist limit which allows the machine to do what? What does this mean?

A
  1. The velocities exceed the Nyquist limit
  2. Fire the next pulse before all of the echoes from the first pulse have returned
  3. This can help raise the Nyquist limit with complication (Range ambiguity)
32
Q

With aliasing, it is possible to do what? The resultant spectral tracing could be what?

A
  1. Pick up flow from more than one depth
  2. Very complex displaying the flow profiles of multiple vessels
33
Q

The sweep speed of the spectral trace can be altered to accommodate for what?

A

Different types of measurements

34
Q

Fast sweeps are used for what measurements? Why?

A
  1. Intracycle measurements
  2. Due to easier calliper placements and increased accuracy for systolic events
35
Q

Slow sweeps are more for what kind of measurements?

A

Intercycle measurements like rate and rhythm

36
Q

CW works much the same as what?

A

Pulsed doppler with a similar block diagram

37
Q

CW has an oscillator that produces what?

A

Continuous AC voltage for motion detection

38
Q

In terms of CW, the echo signal can be sent to what/

A

A speaker or processed into an image just like PW

39
Q

Doppler is sensitive to what?

A

Any motion, not just moving RBCs

40
Q

A wall filter is used to reject what? What is the trade off?

A
  1. The low frequencies from wall motion of pulsatile vessels
  2. If set to high, it can reject real blood velocities in the lower frequency range
41
Q

What does this image represent?

A

Wall filter

42
Q

Colour doppler provides a complete qualitative observation of what/

A

Blood flow analysis over a wide field of view

43
Q

What does colour doppler combines?

A

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

44
Q

What are some synonyms for colour doppler?

A
  1. Colour doppler image
  2. Colour flow imaging
  3. Colour flow mapping
  4. Color doppler
45
Q

How many processes are there to acquire colour doppler?

A

Two

46
Q

What is the process for getting colour doppler? What does this result in?2

A
  1. Standard 2D processes is first followed by the doppler processing
  2. This means several pulses per scan lines are required which has a high impact on the frame rate.
47
Q

Colour doppler is processed using a technique called what?

A

Autocorrelation which is a mathematical means of rapidly determine the sign, mean, power and variance of the returning signal

48
Q

There are typically how many doppler samples displayed per scan line? What does this do?

A

100-400 doppler sakes displayed per scan line which drastically reduces the frame rate

49
Q

With autocorrelation, frame rates of 5- 50 Hz are typically depending on the what?

A

The depth and the size of the field of view

50
Q

Ensemble length (AKA packet size) is what?

A

The number of pulses used for each colour scan line

51
Q

In terms of ensemble length, the colour data represents what?

A

A mean or average of the velocities present

52
Q

To calculate ensemble length, what do we need?

A

A mean velocity, a minimum of 3 pulses are required but more commonly 10 to 20 pulses are used

53
Q

The longer the ensemble length, what happens to frame rate?

A

The slower the frame rate

54
Q

Autocorrelation yields the following information about the blood flow? 4

A
  1. Sign (hue)
  2. Magnitude (saturation)
  3. Power (luminance)
  4. Variance
55
Q

In terms of colour doppler the hue is what?

A

Simply the colour that you can see and represents the sign or direction of flow

56
Q

In terms of colour doppler, saturation is what?

A

The amount of colour in a mix with white and represents the magnitude of the doppler shift or how fast the blood is travelling

57
Q

In terms of colour doppler, more white is what in terms of saturation?

A

Less saturation and faster flow

58
Q

In terms of colour doppler, what is luminance?

A

The brightness of the hue and saturation presented

59
Q

Luminance’s represents what?

A

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

60
Q

More RBC travelling at the same velocity in a sample will appear how on the display?

A

Brighter

61
Q

In terms of colour doppler, variance displays what?

A

The amount of velocities that are different than the mean

62
Q

A variance map can give what?

A

A greater detail than the averaged velocities in a hue or saturation map

63
Q

In terms of colour doppler, what is priority?

A

Priority determines whether or not the colour overlay will overwrite low level echoes

64
Q

If priority is set low then what happens?

A

Precedence is given to non-doppler shifted weak echoes

65
Q

A higher priority allows the colour to do what?

A

To overwrite the low 2D echoes

66
Q

What does this image represent?

A

A mean doppler and a variance display on the right.

67
Q

What is power doppler also known as?

A

Energy mode

68
Q

The colour displayed with power doppler represents what?

A

The strength of the doppler shift as opposed to the velocity

69
Q

What is a disadvantage of setting priority to low?

A

We could override actual issues like thrombus etc.

70
Q

What does this image represent?

A

Priority control, we can see this with the white bar. The image on the right is the same image we just turned up the priority

71
Q

Benefits of power doppler? 3

A
  1. Aliasing
  2. Less dependant on angle
  3. Very sensitive to low flow states
72
Q

The down side of power doppler is what? 3

A
  1. There is no direction,
  2. Flow speed or character information
  3. Very susceptible to blooming artifacts

Phys 314 Physics 3 (11 decks)

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