Colour Doppler Flashcards

1
Q

what information do doppler instruments provide on blood flow? (4)

A

presence
speed
character
direction

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2
Q

what are the three types of doppler displays

A

colour
spectral
audible

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3
Q

what does colour doppler do/incorporate?

A

pulsed echo imaging + doppler shifted

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4
Q

what does the colour doppler display on the screen

A

parallelogram because of steering (to get closer to zero)

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5
Q

one pulse per scan line is colour doppler true or false

A

false. multiple pulses sent out (3-32***) per scan line in doppler colour. one pulse per scan line is in B-mode

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6
Q

autocorrelation

A

determines mean and variance of the doppler shift signal, done in the signal processor

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7
Q

ensemble length

A

number of pulses per scan line

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8
Q

What is the ensemble length for colour doppler

A

3-32

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9
Q

what happens when you increase ensemble length?

A

frame rate decreases

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10
Q

what is the process that detects doppler shifts in colour doppler instruments

A

autocorrelation

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11
Q

ensemble length needs to be higher for these conditions (3)

A

sensitivity
accuracy of speed calculation

this decreases temporal resolution however!

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12
Q

4 parameters of the signal processor

A

direction*
velocity*
variance*
power/strength

*colour map helps to interpret

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13
Q

what does power depend on

A

concentration of RBC
impedence (higher z mismatch, more reflection)
reflectors (specular vs scattering)

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14
Q

changing the colour map does what

A

decreases temporal resolution

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15
Q

colour map helps to interpret (3)

A

direction
velocity
variance

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16
Q

invert

A

flips the colour map - top is positive shift

say if you want arteries to be red but direction is away

17
Q

baseline

A

can move BL up or down if you want more of one direction of flow

18
Q

PRF is proportionate to the

A

scale/velocity range

19
Q

what happens if your scale is set too high

A

slower flows go undetected

20
Q

aliasing happens when

A

PRF is set too low

21
Q

what is aliasing and what does it depend on

A

shows wrap around colour, depends on the nyquist limit which is 1/2 PRF

22
Q

if PRF = 16 KHz a doppler shift of anything over what would alias? how do you get rid of this artifact?

A

Anything over 8 KHz (nyquist limit 1/2 PRF) would alias

Increase PRF

23
Q

What happens once the instrument processes the doppler data?

A

it goes to the display

24
Q

what are the colour display parameters (3)

A

hue
saturation
luminance

25
what colour is shown is what type of display parameter
hue
26
brightness is what type of display parameter
luminance
27
what is saturation
amount of a colour
28
wall filter
gets rid of clutter, eliminates lower frequency doppler shift caused by tissue motion
29
what happens if you increase PRF too much to get rid of aliasing?
echo misplacement
30
true or false - you can use aliasing to your advantage in stenosis
true - highlights areas of highest velocity
31
priority
greyscale vs colour threshold - echoes below cut off amplitude will show as colour. Stronger echoes will be grey scale
32
in priority, echoes below cut-off amplitude will show as what? and echoes above cut-off amplitue will show as
below cut off amplitude = colour | above cut off amplitude = greyscale
33
Limitations to colour doppler (5)
1. sonographer skill 2. body type 3. aliasing 4. Angle dependence 5. Tortuous vessels may look like flow reversal or aliasing
34
power doppler displays
related to amplitude / concentration of RBC
35
what is the only thing power doppler displays do?
only shows presence of flow
36
advantages of power doppler (4)
``` independent of doppler shift independent of doppler angle no aliasing (same as CW) improved sensitivity (deeper penetration, smaller vessels, slower flows) ```
37
disadvantages of power doppler
no directional information no flow speed information no flow character information