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Physics 3 > Module 7 : Doppler > Flashcards

Module 7 : Doppler Flashcards

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1
Q

is the frequency lower in doppler or 2D why

A
  • doppler

- account for attenuation for the attenuation from the RBC’s

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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
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3
Q

what is doppler shift detection the result of

A
  • quadrate phase detector
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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
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5
Q

what two devices can the resultant doppler signal be sent to after quadrate phase detection

A
  • loudspeaker

- spectral analyzer for image processing

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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

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7
Q

what does the spectrum analyzer do

A
  • separates the individual doppler shifts from the complex beat frequency
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8
Q

what is the spectrum analyzer synonymous too

A
  • prism separating white light into a rainbow
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9
Q

what is fast Fourier transform FFT

A
  • the process through which doppler signals are separated into doppler shifted frequencies
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10
Q

what does FFT break the complex doppler shift signal into

A
  • not its component/separate frequencies displaying both MAGNITUDE AND AMPLITUDE
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11
Q

how many spectra per second can FFT produce

A

100-1000

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12
Q

what axis are the operate doppler shifts plotted on

A
  • the y axis
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13
Q

what is the magnitude of the doppler shift

A
  • amount of positive or negative shift
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14
Q

what is a + 4 kHz doppler shifts magnitude equal too

A
  • same as magnitude of -4kHz shift
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15
Q

what are the 3 factors affecting magnitude

A
  • RBC velocity
  • angle of insonation
  • operating frequency
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16
Q

what is the amplitude(brightness) of the doppler shift

A
  • represents the number of RBCs that are contained with the sample volume
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17
Q

what are the 4 factors affecting amplitude

A
  • RBC density
  • attenuation
  • power
  • gain
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18
Q

what does an increase in RBC density affect amplitude

A
  • increase amplitude
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19
Q

what does an increase in attenuation affect amplitude

A

decrease amplitude

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20
Q

what does an increase in power and gain affect amplitude

A
  • decrease in amplitude
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21
Q

what three things is the sample volume comprised of

A
  • beam width
  • gate length (range gated)
  • pulse length
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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
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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
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24
Q

what limits the amount of sampling

A
  • DEPTH

- limits the PRF

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25
Q

what is the limit exceeded when aliasing occurs and what value is it

A
  • nyquist limit

- 1/2 PRF

26
Q

what are the 5 ways to correct for aliasing

A
  • 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
Q

what 2 methods do we use clinically to correct for aliasing

A
  • changing the baseline

- increase PRF

28
Q

what happens when a machine operates in a high PRF mode

A
  • allows machine to fire next pulse before all of the echoes from the first pulse have been returned
  • raises the nyquist limit
29
Q

what is one consequence of using high PRF mode

A
  • range ambiguity

- if more than one vessel is on the screen we may pick up a trace from more than one vessel

30
Q

what are fast sweep speeds used for

A
  • intracycle measurements due to caliper placements and increased accuracy for systolic events
31
Q

what are slow sweep speeds used for

A
  • intercycle measurements

- rate and rhythm

32
Q

what mechanisms control the CW probe

A
  • has an oscillator that produces an continuous AC voltage for motion detection
33
Q

is doppler only sensitive to RBC flow

A
  • no
34
Q

what is wall filter used for

A
  • reject the low frequencies from wall motion of pulsatile vessels
35
Q

what can be a consequence of too high of wall filter

A
  • if too high it can reject real blood velocities in the lower frequency range
36
Q

what is the main thing that color doppler provides us with

A
  • qualitative blood flow analysis over a wide field of view
37
Q

what 2 things does color doppler combine

A
  • anatomical detail of 2D image and physiological hemodynamics with color overlay
38
Q

what are 4 other names for color doppler

A
  • color doppler imaging CDI
  • color flow imaging CFI
  • color flow mapping CFM
  • color doppler CD
39
Q

what are the 2 processes required to display color doppler

A
  • standard 2D processing

- doppler processing

40
Q

how many pulses per scan line are required for a color doppler image

A
  • 4 pulses
  • 1 for 2D
  • 3 for color
  • HUGE IMPACT ON FRAME RATE
41
Q

how is color doppler processed

A
  • autocorrelation
42
Q

what is autocorrelation

A
  • mathematical means of rapidly determining the sign, mean, power and variance of retuning signal
43
Q

what is ensemble length

A
  • aka packet size

- number of pulses used for each color scan

44
Q

what does color data represent

A
  • mean or average of the velocities present
45
Q

what does a longer ensemble length mean for the frame rate

A
  • slower frame rate
46
Q

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

A
  • 3

- 10 or 20

47
Q

what 4 things does autocorrelation yield

A
  • sign (HUE)
  • magnitude (SATURATION)
  • power (LUMINANCE)
  • VARIANCE
48
Q

what is the hue

A
  • the color you see and represents the sign or direction of flow
  • tells us a bit about magnitude too
49
Q

what is the saturation

A
  • amount fo color in a mix with white and represents the magnitude of the doppler shift or how fast the blood is traveling
50
Q

what does a more white saturation mean for flow velocity

A
  • faster flow
51
Q

what is luminance

A
  • brightness of the hue and saturation presented
52
Q

what does luminance represent

A
  • power of flow and RBC density within the field of view
53
Q

what will more RBCs travelling at the same velocity appear as

A
  • brighter on display
54
Q

what is variance

A
  • displays the amount of velocities that are different than the mean
  • how far away from the mean we are
55
Q

how can a variance map help us more than mean velocity

A
  • give greater detail

- can pinpoint an area of disease

56
Q

what is color priority

A
  • determines whether or not the color overlay will overwrite the low level echoes
57
Q

what is given preceded in color priority is low

A
  • non doppler shifted weak echoes
58
Q

what is given precedence when color priority is set high

A
  • color will overwrite the low 2D echoes
59
Q

what is power doppler also known as

A
  • energy mode

- color power angio CPA

60
Q

what is power doppler

A
  • color displayed represents the strength of the doppler shift as opposed to the velocity
61
Q

what are 3 advantages to power doppler

A
  • free of aliasing
  • less dependant on angle
  • sensitive to low flow states
62
Q

what are 4 disadvantages to power doppler

A
  • non direction
  • flow speed
  • character information (laminar flow or not)
  • very susceptible to blooming artifacts

Physics 3 (5 decks)

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