Module 7 : Doppler Flashcards
(62 cards)
1
Q
is the frequency lower in doppler or 2D why
A
- doppler
- account for attenuation for the attenuation from the RBC’s
2
Q
how many pulses are sent out for spectral doppler
A
- 2
- one for 2D that is shorter
- one for spectral that is longer
+ more time to interact with the cardiac cycle
3
Q
what is doppler shift detection the result of
A
- quadrate phase detector
4
Q
what is a quadrate phase detector
A
- transmitted signal (reference) is duplicated and stored
- the reference signals are the same except they are 1/4 OUT OF PHASE WITH EACH OTHER
- returning signal is compared to the reference signal to determine the positive or negative shift
5
Q
what two devices can the resultant doppler signal be sent to after quadrate phase detection
A
- loudspeaker
- spectral analyzer for image processing
6
Q
what does the doppler shifted signal contain and is it simple or complex
A
- all of the shifts that occur in the sample gate
- complex
7
Q
what does the spectrum analyzer do
A
- separates the individual doppler shifts from the complex beat frequency
8
Q
what is the spectrum analyzer synonymous too
A
- prism separating white light into a rainbow
9
Q
what is fast Fourier transform FFT
A
- the process through which doppler signals are separated into doppler shifted frequencies
10
Q
what does FFT break the complex doppler shift signal into
A
- not its component/separate frequencies displaying both MAGNITUDE AND AMPLITUDE
11
Q
how many spectra per second can FFT produce
A
100-1000
12
Q
what axis are the operate doppler shifts plotted on
A
- the y axis
13
Q
what is the magnitude of the doppler shift
A
- amount of positive or negative shift
14
Q
what is a + 4 kHz doppler shifts magnitude equal too
A
- same as magnitude of -4kHz shift
15
Q
what are the 3 factors affecting magnitude
A
- RBC velocity
- angle of insonation
- operating frequency
16
Q
what is the amplitude(brightness) of the doppler shift
A
- represents the number of RBCs that are contained with the sample volume
17
Q
what are the 4 factors affecting amplitude
A
- RBC density
- attenuation
- power
- gain
18
Q
what does an increase in RBC density affect amplitude
A
- increase amplitude
19
Q
what does an increase in attenuation affect amplitude
A
decrease amplitude
20
Q
what does an increase in power and gain affect amplitude
A
- decrease in amplitude
21
Q
what three things is the sample volume comprised of
A
- beam width
- gate length (range gated)
- pulse length
22
Q
what is an important consideration to take into account for with PW sample volume in regards to the beam characteristics
A
- its a 3D sample volume that changes in size relative to depth
- when placed in the farfield it becomes larger
23
Q
why does aliasing occur
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
24
Q
what limits the amount of sampling
A
- DEPTH
- limits the PRF
25
what is the limit exceeded when aliasing occurs and what value is it
- nyquist limit
| - 1/2 PRF
26
what are the 5 ways to correct for aliasing
- change baseline (depending on direction of flow)
- increase PRF (scale) (aka velocity range)
- lower frequency (already lowest)
- increase doppler angle (inaccurate)
- switch to CW (only w/ a capable probe)
27
what 2 methods do we use clinically to correct for aliasing
- changing the baseline
| - increase PRF
28
what happens when a machine operates in a high PRF mode
- allows machine to fire next pulse before all of the echoes from the first pulse have been returned
- raises the nyquist limit
29
what is one consequence of using high PRF mode
- range ambiguity
| - if more than one vessel is on the screen we may pick up a trace from more than one vessel
30
what are fast sweep speeds used for
- intracycle measurements due to caliper placements and increased accuracy for systolic events
31
what are slow sweep speeds used for
- intercycle measurements
| - rate and rhythm
32
what mechanisms control the CW probe
- has an oscillator that produces an continuous AC voltage for motion detection
33
is doppler only sensitive to RBC flow
- no
34
what is wall filter used for
- reject the low frequencies from wall motion of pulsatile vessels
35
what can be a consequence of too high of wall filter
- if too high it can reject real blood velocities in the lower frequency range
36
what is the main thing that color doppler provides us with
- qualitative blood flow analysis over a wide field of view
37
what 2 things does color doppler combine
- anatomical detail of 2D image and physiological hemodynamics with color overlay
38
what are 4 other names for color doppler
- color doppler imaging CDI
- color flow imaging CFI
- color flow mapping CFM
- color doppler CD
39
what are the 2 processes required to display color doppler
- standard 2D processing
| - doppler processing
40
how many pulses per scan line are required for a color doppler image
- 4 pulses
- 1 for 2D
- 3 for color
- HUGE IMPACT ON FRAME RATE
41
how is color doppler processed
- autocorrelation
42
what is autocorrelation
- mathematical means of rapidly determining the sign, mean, power and variance of retuning signal
43
what is ensemble length
- aka packet size
| - number of pulses used for each color scan
44
what does color data represent
- mean or average of the velocities present
45
what does a longer ensemble length mean for the frame rate
- slower frame rate
46
to calculate a mean velocity what is the minimum number of pulses that need to be sent out and what is the usual number sent out
- 3
| - 10 or 20
47
what 4 things does autocorrelation yield
- sign (HUE)
- magnitude (SATURATION)
- power (LUMINANCE)
- VARIANCE
48
what is the hue
- the color you see and represents the sign or direction of flow
- tells us a bit about magnitude too
49
what is the saturation
- amount fo color in a mix with white and represents the magnitude of the doppler shift or how fast the blood is traveling
50
what does a more white saturation mean for flow velocity
- faster flow
51
what is luminance
- brightness of the hue and saturation presented
52
what does luminance represent
- power of flow and RBC density within the field of view
53
what will more RBCs travelling at the same velocity appear as
- brighter on display
54
what is variance
- displays the amount of velocities that are different than the mean
- how far away from the mean we are
55
how can a variance map help us more than mean velocity
- give greater detail
| - can pinpoint an area of disease
56
what is color priority
- determines whether or not the color overlay will overwrite the low level echoes
57
what is given preceded in color priority is low
- non doppler shifted weak echoes
58
what is given precedence when color priority is set high
- color will overwrite the low 2D echoes
59
what is power doppler also known as
- energy mode
| - color power angio CPA
60
what is power doppler
- color displayed represents the strength of the doppler shift as opposed to the velocity
61
what are 3 advantages to power doppler
- free of aliasing
- less dependant on angle
- sensitive to low flow states
62
what are 4 disadvantages to power doppler
- non direction
- flow speed
- character information (laminar flow or not)
- very susceptible to blooming artifacts
