PHY- Doppler Flashcards
(104 cards)
1
Q
define Doppler effect
A
change in frequency caused by the motion of a source, reflector or receiver
2
Q
examples of doppler affect? (4)
A
- weather forecasting
- police radar
- door openers
- burgler alarms
3
Q
Define dopper shift and give examples
A
- quantification of the change in frquency
getting closer, frequency ↑ (positive shift)
getting farther, frequency ↓ (negative shift)
4
Q
Doppler 4 steps?
A
- Transducer sends a pulse to moving object
- transducer receives the new frequency and calculates doppler shift doppler shift
- doppler shift depends on the objects velocity
- machine calculated speed based on doppler shift
5
Q
what does the doppler shift depend on?
A
- Objects velocity
- cosine of doppler angle
6
Q
if the angle of interrogation is non-zero what will occur?
A
Lesser dopper shift with occur
7
Q
why do we incorporate cos 0 to dopper shift?
A
to compensate for the lesser shift
8
Q
What is doppler angle?
A
the angle of incident beam to the direction of blood flow
9
Q
cosine 0, 30, 60, 90 degrees?
A
cos 0= 1
cos 30= 0.87
cos 60= 0.5
cos 90= 0
10
Q
to achieve an angle close to zero the sonographer must?
A
- heel-toe
- phase (steer)
11
Q
define doppler ultrasound characteristics (4)
A
presence, speed, character and direction of blood flow
12
Q
what are the 3 characteristics of doppler ultrasound display?
A
- colour
- spectral
- audible
13
Q
what information are we getiing from colour doppler (4)
A
- presence
- speed
- character
- direction
14
Q
how is doppler shift detected?
A
- beam former sends digitized voltages to signal processor
- signal processor detect dopper shifted echoes using autocorrelation
15
Q
what detects shifted echos and using what?
A
- signal processor detects doppler shifted echos using autocorrelation
16
Q
define autocorrelation
A
mathematical technique that determines mean and variance of doppler shift signal
17
Q
what 4 things does autocorrelation determine?
A
- mean of doppler shift signal
- variance of doppler shift signal
- power
- sign
18
Q
how many pulses are sent out per scan line?
A
3-32
19
Q
pros and cons of multiple pulses being sent out per scan line
A
pros: increased accuracy and sensitivity (picking out weaker echoes/shifts)
cons: decreased frame rate
20
Q
what does autocorrelation calculate and display? (4)
A
- average velocity
- distribution of velocities
- strength of echoes
sign -/+
21
Q
what is power? what is it related to?
A
- the intensity of an echo
- related to the amplitude
22
Q
what does power depend on? (3)
A
- reflectors
- impedance
- concentration of RBC’s
23
Q
more relection =
A
more reflection, more echo
24
Q
higher delta z =
A
more echo
25
higher concentration of RBC's =
more reflectors, more echo
26
what does power doppler use?
ONLY uses the power/strength of doppler shifts
27
pros of power doppler?
- increased sensitivity
- no angle dependence
- no aliasing
28
cons of power doppler? (4)
- no direction
- no flow sleed
- no flow character info
- cannot detect a stenosis
29
3 colour display parameters?
1. hue
2. saturation
3, luminance
30
what is saturation?
richness of colour
31
what is luminance?
brightness of colour
32
9 colour controls?
1. box
2. colour map
3. colour invert
4. baseline
5. PRF
6. gain
7. wall filter
8. ensemble length
9. priority
33
baseline AKA?
zero point
34
to show more positive flows what should you do to the baseline?
move it down
35
changing PRF will change our?
scale
36
what does lowering the PRF do?
- allows to pick up slower flow
| - increases chance of aliasing
37
aliasing depends on?
Nyquist limit
38
pros of aliasing?
can highlight the fastest speeds within a stenosis
39
where in the instrument does gain occur?
amplifiers of beam former
40
what is wall filter?
cutting off slower flows/tissue motion
41
ensemble length AKA?
packet size
42
what is ensemble length?
number of pulses used for each colour scan line
43
priority AKA?
threshold
44
what is priority?
- echos below cut-off amplitude will show colour
| - stronger echoes show as grayscale
45
if priority iof set too low what occurs?
- noise or artifacts within the vessel are displayed with little colour
46
if priority of set too high what occurs?
fills the vessel with colour
| - when there is a low signal-to-noise ratio
47
4 colour limitaitons?
1. angle dependence
2. low FR
3. lack of spectral info
4. sonographer skill
48
what is duplex scanning?
- doppler = gray scale imaging
- Transducer does one at a time
- simultaneous does exist but decreased FR- rapidly switches between the two
49
In practice, approximately _____ pulses are required to obtain one line of color Doppler information?
10
50
Lack of color in a vessel with blood flow may be attributable to ______ (3)
- low colour gain
- high wall filter setting
- low priority setting
51
Increasing ensemble length ____ color sensitivity and accuracy and ________ FR
- improves, decreases
52
What color control helps with clutter?
wall filter
53
Color map baselines are always represented by what color?
black
54
steering the color window to the right or left changes _____? (2)
- doppler shift
| - doppler angle
55
In a single frame, color can be different ( red and blue) in a vessel because of ____? (4)
- Vessel curvature
- Sector format
- Helical flow
- Diastolic flow reversal
56
Doppler power imaging indicates the _______ of flow
presence
57
what info are we getting from spectral doppler? (4)
1. presence
2. direction
3. character
4. speed
58
Pulse generates pulses _____ cycles long
59
what determines doppler shift accurately?
longer pulse
60
spectral doppler characteristics? (3)
1. pulser
2. detector
3. spectrum analyzer
61
the detector is part of what element?
signal processor
62
function of detector?
- echo voltages are amplified
| - doppler shifts determined by comparing to pulser frequency
63
2 things that contribute to the detecor?
1. mixer (fR+ fT) and (fR-fT)
| 2. filter (gets rid of sum)
64
function of spectrum analyzer?
generates doppler shift spectral displays using fast Fourier transform
65
the spectrum analyzer generates doppler shift spectral displays using?
fast fourier transform
66
what is fast fourier transform?
mathematical technique for spectral doppler
** remember autocorrelation is the mathematical tequnique for colour doppler
67
The amplitude or power of each Doppler shift is shown as?
brightness
68
dark spots on spectral display means that doppler shift is?
very weak or nonexistant
69
what is range gating?
ability to take motion information from a specific depth
70
gate amplifier is found in?
beam former
71
the gate amplifier takes samples from? (2)
1. specific sample volume (gate)
| 2. specific depth
72
what is gate width?
wb
| - At the sample volume depth
73
when to use longer gate- gate length?
when searching for a vessel or flow location
74
when to use a shorter gate- gate length?
for spectral analysis and evaluation
75
a shorter gate improves?
the quality of the spectral display
76
What is spectral broadening? when is it seen? what does it cause?
- vertical thickening of the spectral trace
- seen with wider range of velocities
- causes narrowing of window
77
reasons for spectral broadening?
- disturbed or turbulent flow
78
what is artificial spectral broadening?
- excessive doppler gain
| - excessive sample volume length
79
8 spectral controls?
1. gate size/ sample volume
2. gain
3. spectral invert
4. baseline
5. PRF
6. wall filter
7. angle correct
8. audio
80
with gain there is potential for?
- amplifications of echos
| - potential for noise and spectral broadening
81
increasing angle, decreases?
- doppler frequency
- velocity
- makes it seem lower than it is
82
audio- higher frequency =
higher pitch
83
what is CW doppler?
- 2 transducer elements- one to send, one to receive
- very small probe
- sample volume is large in overlapping area
84
beacuse sample volume is large with CW doppler what occurs?
- poor range resolution and ability to determine depth of reflectors
85
T or F CW doppler can alias?
- False
| - no PRF in CW
86
If angle correction is set at 60 degrees but should be zero degrees, the display indicates a flow speed of 100 cm/s
The correct flow speed is _____ cm/s.
50
87
If angle correction is set at 0 degrees but should be 60 degrees, the display indicates a flow speed of 100 cm/s
The correct flow speed is _____ cm/s.
200
88
If a 5-kHz Doppler shift corresponds to 100 m/s, a 2.5-kHz shift corresponds to ____ m/s
50
89
Which of the following is increased if Doppler angle is increased?
a. Aliasing
b. Doppler shift
c. Effect of angle error
d. b and c
e. None of the above
effect of angle error
90
Color-Doppler frame rates are ______ gray-scale rates
less than
91
Decreased distal resistance normally causes end diastolic flow to ________.
increase
92
Flow reversal in diastole indicates ______.
high distal resistance
93
T or F With angle correct incorporated, higher flow speed always produces a higher Doppler shift on spectral display.
true
94
Higher operating frequency produces a higher Doppler shift on spectral display. T or F
true
95
Does higher freq transducer overestimate velocity?
no
96
As stenosis progresses, which of the following increases?
a. Lumen diameter
b. Systolic Doppler shift
c. Diastolic Doppler shift
d. Spectral broadening
e. more than one of the above
e. (b,c,d)
97
Disturbed flow produces narrower spectrum?
false
98
T or F- Turbulent flow produces a narrower spectrum?
false
99
If all the cells in a vessel were moving at the same constant speed, the spectral trace would be _____________.
a. thin horizontal line
b. thick horizontal line
c. as in descending aorta
d. tardus parvus
e. depends on velocity
thin horizontal line
100
stenosis effect?
```
Peak systolic flow speed
End diastolic flow speed
Spectral broadening
Window
Envelope
```
101
T or F: Doppler ultrasound provides information about flow conditions only at the site of measurement.
False
102
Doppler signal power (or amplitude) is proportional to _______.
cell concentration
103
Compared with Doppler-shift imaging, Doppler-power imaging is _______.
More sensitive
Angle independent
Aliasing free
Speed independent
104
Doppler-power imaging indicates (with color) the _____ of the flow.
presence
