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DMSO Physics 2 > Doppler > Flashcards

Doppler Flashcards

(67 cards)

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1
Q

Doppler Shift (Doppler Frequency)

A

The change or variation in the freq of sound as a result of motion between the sound source and the receiver

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2
Q

What is the difference between received and transmitted frequencies?

A

Doppler shift

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3
Q

When reflected frequency is higher than transmitted?

A

positive change

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4
Q

reflected freq is less than transmitted?

A

negative change

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5
Q

Doppler measures _____ not _______

A

frequency shift, not amplitude

velocity, not speed

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6
Q

untis of freq

A

Hz

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7
Q

Typical audible values created when sound reflects off of RBC’s

A

20Hz-20 kHz

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8
Q

flow towards the transducers?

A

increased freq

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9
Q

flow away from the transducers

A

decreased frequencies

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10
Q

frequency shift is related to what?

A

velocity

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11
Q

2 MHz-10 MHz transducers are usedto preform doppler ultrasound studies, but doppler shift ranges from?

A

20Hz-20kHz

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12
Q

The process of extracting the Doppler freq (low) form the transducer frequency (high)?

A

demodulation

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13
Q

Doppler shift=

A

received freq - transmitted freq

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14
Q

doppler equation

A

doppler shift= 2xrefelctor speedxincident frequencyxcos angle/ prop speed

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15
Q

Doppler shift is directly related to:

A

RBC speed, frequency of transducer, cos of angle between flow and sound beam

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16
Q

Doppler shift is inversely related to:

A

speed of sound in the medium

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17
Q

velocity (measured)=

A

true velocityxcos angle

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18
Q

Non-choerent processing used with what

A

uni-directional doppler

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19
Q

ultrasound system that displays real-time images and Doppler simultaneously is called?

A

duplex

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20
Q

Phase quadrature processing used in?

A

bidirectional doppler

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21
Q

number of cyrstals in a CW doppler

A

2

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22
Q

Advantage of CW doppler

A

Able to measure very high velocities

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23
Q

Disadvantage of CW Doppler

A

range ambiguity

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24
Q

Echoes arise from entire length of overlap between the transmit and receive beams

A

range ambiguity

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25
how manycrystals are needed for PW Doppler
1
26
Advantage of PW Doppler
Echoes only arise from the area of integration, ample volume or gate. We adjust the receive gate. Range resolution
27
Disadvantage of PW doppler
Aliasing, errors in measuring high velocities
28
High velocity measurements are inaccurate if the pulsed Doppler sampling rate is too low in comparison to measured blood velocity?
Aliasing
29
What should be done to improve the ability to measure the max velocity with Doppler?
Eliminate aliasing
30
The doppler freq at which aliasing occurs
Nyquist limit (nyquist freq)
31
PRF/2
Nyquist limit (kHz)
32
Aliasing is more likely to occur with higher or lower frquencies?
Higher
33
Five ways to eliminate aliasing
1. adjust scale 2. select transducers with low freq 3. select new view with shallower sample volume 4. use CW doppler 5. baseline shift
34
PRF and Nyquist limit are lower with shallower or deeper sample volumes?
deeper
35
\_\_\_\_\_\_ sampler volumes (gates) create Doppler spectra with larger, cleaner envelopes
smaller
36
Larger sample volumes create doppler sepectra with smaller envelopes known as what?
Spectral broadening
37
The horizontial axis of a doppler spectrum is?
time
38
The vertical axis of a Doppler spectrum is?
doppler shift or velocity
39
relationship between transducer frequency and doppler shift
when freq is halved, doppler shift is half
40
Gray shades on a Doppler spectrum are related to:
Amplitude of the reflected signal or the number of RBC's creating the reflection
41
pulsed doppler
1. Min of one crystal 2. range resolution 3. limit on max velocity 4. damped, low Q, wide bandwidth
42
Continuous Doppler
1. min of two crystals 2. range ambiguity, region of overlap 3. unlimited max velocity 4. undamped, high Q, narrow bandwidth
43
imaging transducers
1. normal incidence 2. higher freq- improved resolution 3. pulsed wave only 4. at least 1 crystal
44
Doppler transducers
1. 0 to 180 degrees 2. lower freq 3. pulsed or CW 4. 1 (PW) or 2 (CW) crystals
45
color doppler reports
average velocities
46
variance mode
color map that varies side to side. left side: laminar right side: turbulent
47
Which setting has the greatest effect on jet size?
Color doppler gain
48
Multiple ultrasound pulses are needed to accurately determine RBC velocities by doppler?
A packet or ensemble length
49
Advantages of more pulses in the packet
greater accuracy of the velocity measurement sensitivity to low flow
50
disadvantages of more pulses in the packet?
More time is required to acquire info frame rate is reduced temporal resolution is decreased
51
Why does color doppler measure mean velocity?
the packet size must balance between accurate velocity measurements and temporal resolution
52
Synonyms for power doppler
energy mode or color angio
53
Advantages of power doppler
1. increased sensitivity to low flow 2. not effected by doppler angle unless 90 degrees 3. no aliasing
54
limitations of power doppler
1. no measurement of velocity 2. slower frame rates 3. susceptible to motion (flash artifact)
55
performed to extract or identify the individual freq making up a complex signal?
spectral analysis
56
Spectral analysis method for pulsed or CW doppler
Fast Fourier transform
57
spectral analysis for color flow doppler
autocorrelation or correlation function
58
FFT and autocorrelation are what type of techniques
digital
59
used due to the large amount of Doppler information that requires processing?
Autocorrelation Slightly less accurate, but faster than FFT
60
Can a successful Doppler exam be preformed regardless of a patients hematocrit?
yes
61
Ghosting
Low velocity motion from pulsating vessel walls can also produce small doppler shifts that bleed into surrounding anatomy
62
High pass filter
Eliminates low magnitude Doppler shifts that are created from moving anatomy rather than red blood cells
63
Wall filters are used to reject?
Clutter
64
color flash is also called?
ghosting
65
Cross talk is in?
doppler only
66
Special form of mirror image where the Doppler spectrum appears above and below the baseline?
Cross talk
67
Cause of crosstalk
Doppler gain set too high Incident angle near 90 degrees when flow is at focus

DMSO Physics 2 (26 decks)

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