Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

PHYS 314 > Doppler > Flashcards

Doppler Flashcards

1
Q

How does the frequency for Doppler differ from the frequency for 2D images?

A

Doppler frequency is lower to account for the attenuation from the RBC’s

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How does the pulser improve accuracy when using doppler?

A

It generates longer 5-30 cycle pulses so that the entire cardiac cycle can be observed.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

The Doppler shift detection is typically the result of what?

A

Quadrature phase detector

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is a quadrature phase detector? (4 steps)

A
  1. The transmitted signal is duplicated and stored (copied)
  2. The two signals are sent out 1/4 out of phase with eachother.
  3. The returning signal is compared to the transmitted signal to determine a pos or neg shift
  4. Signal sent to a loudspeaker or spectral analyzer for image processing
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

The Doppler shift signal contains what?

A

It is complex and contains all the shifts that occur in the sample gate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does the spectrum analyzer do?

A

It is a means of separating the individual Doppler shifts from the complex beat frequency (like a prism separating white light into colours)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is fast fourier transform?

A

The process by which doppler signals are separated into Doppler shifted frequencies

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

The Fast Fourier Transform analyzes the complex Doppler shift signal and then breaks it down by displaying what?

A

Magnitude and amplitude

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is magnitude?

A

The amount of positive or negative shift

Ex. Can be +4 kHz or -4kHz (same magnitude)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What does the amplitude of the Doppler shift represent?

A

Number of RBC’s that are contained within the sample volume

Ex. Two 4 kHz shifts have the same magnitude

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the doppler shift equation?

A

Change in f = (2 X fo X vel X Costheta) / C

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Sample volume is comprised of what? (3)

A

Beam width, gate length, and pulse length

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What limits the amount of sampling?

A

Aliasing: when the Nyquist limit is exceeded (1/2 PRF is exceeded)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the 5 ways to correct for aliasing?

A
  1. Change the baseline
  2. Increase the PRF/ scale (sample faster)
  3. Lower the frequency
  4. Increase the Doppler angle
  5. Switch to CW (no image)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is high PRF mode?

A

When the velocities exceed the Nyquist limit some machines are able to fire the next pulse before waiting for all of the echoes to return

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are fast sweeps used for? Why?

A

Intracycle measurements. Easier caliper placement and increased accuracy for systolic events

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are slow sweeps used for?

A

Intercycle measurements like rate and rhythm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

CW has an oscillator that produces what?

A

A continuous AC voltage for motion detection

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Since Doppler is sensitive to any motion, what is used to reject low frequencies from motion?

A

Wall filter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is a consequence of setting the wall filter too high or too low?

A

Too high = It can reject real blood velocities in the lower frequency range (near baseline)

Too low = clutter and distortion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What are synonyms for Colour Doppler?

A

Colour Doppler Imaging (CDI), Colour Flow Imaging (CFI), Colour Flow Mapping (CFM)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Colour Doppler is processed using a technique called what?

A

Autocorrelation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Ensemble length is another way of saying what?

A

Packet size (Number of pulses used for each colour scan line)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is another name for sign, magnitude and power?

A

Sign = Hue

Magnitude = Saturation

Power = Luminance

25
Q

How does the ensemble length affect frame rate?

A

Longer ensemble length = slower frame rate

26
Q

Better luminance =

A

A better signal

27
Q

Define ‘hue’:

A

Color that you see, represents sign (direction of flow)

28
Q

Define ‘saturation’:

A

Represents the magnitude of the Doppler shift or how fast the blood is travelling (More white = less saturation, faster flow)

29
Q

Define ‘luminance’:

A

Brightness of the hue and saturation. Represents the power of the flow, tells us the RBC density

30
Q

Define ‘variance’:

A

Displays the amount of velocities that are different than the mean (gives more detail than averaged velocities seen in a hue or saturation map).

31
Q

Define ‘priority’ and low/high:

A

Determines whether or not the colour overlay will overwrite the low level echoes

High priority = precedence to colour (may overwrite pathology)
Low priority = precedence to 2D

32
Q

Energy mode is also known as what?

A

Power Doppler

33
Q

In Power Doppler, the colour displayed represents what?

A

Strength of the Doppler shift (instead of velocity)

34
Q

Name the pros (3) and cons (4) of power Doppler:

A

Pros:

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

Cons:

  • No direction
  • No flow speed
  • No character info
  • Susceptible to blooming artifact
35
Q

Does the transducer differ between 2D and Doppler applications?

A

No

36
Q

How do you determine if flow is in phase or out of phase?

A

Quadrature Phase Detector

37
Q

What is another name for the transmitted signal?

A

Reference signal

38
Q

What is considered “good” doppler and what range can FFT produce?

A

FFT = 100-1000 spectra per second

Good Doppler = 1000 spectra per second

39
Q

How are the doppler shifts plotted?

A

On the y-axis (over time)

40
Q

What are the factors affecting magnitude?

A

All elements of the doppler shift equation and:

  • RBC velocity
  • Angle of insonation
  • Operating frequency

Know relationships

41
Q

What are the factors affecting amplitude (brightness)?

A
  • RBC density (increase)
  • Attenuation (decrease)
  • Power and gain (increase)
42
Q

How does the PW Doppler sample volume change?

A

It is a 3 dimensional volume that changes in size relative to depth, when placed in the far field it will be very large.

43
Q

What is responsible for picking up the waveforms of two neighbouring vessels simultaneously?

A

Sample volume

44
Q

Where does FFT happen?

A

Spectrum analyzer

45
Q

What is bin?

A

The density of RBC’s at a certain time (brightness) similar to a pixel

46
Q

Why can the amplitude be inaccurate?

A

Due to scatter (constructive and deconstructive interference changes the amplitudes artificially)

47
Q

What artifact are small gates associated with?

A

Spectral Broadening

48
Q

A low saturation will have what velocity?

A

High velocity = low saturation (white)

49
Q

What is the consequence of High PRF mode?

A

Range ambiguity where flow may be picked up from more than one depth resulting in a spectral tracing of multiple vessels due to multiple gates

50
Q

What is a good solution for aliasing in echo?

A

Switch to CW

51
Q

What can be done with a CW echo signal?

A
  • Sent to speaker

- Processed into an image

52
Q

Why does doppler affect frame rate?

A

Several pulses per scan line are needed for 2D with colour overlay (reduces frame rate)

53
Q

What is the minimum amount of pulses needed for CD?

A

3

54
Q

What is autocorrelation? (5)

A

A mathematical means of quickly determining the sign, mean, magnitude, power and variance of the returning signal.

55
Q

How many doppler samples are typically displayed per scan line and what does this affect?

A

100-400

Reduces frame rate

56
Q

What frame rate does colour doppler have?

A

5-50 Hz

57
Q

What does the colour data in an image represent?

A

The mean or average of the velocities present

58
Q

How many pulses are required to calculate a mean velocity?

A

Min = 3 pulses

Common = 10-20 pulses (more accurate)

59
Q

If variance is on, what may be seen?

A

Aliasing (more velocities).

PHYS 314 (5 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions