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Physics > Colour Doppler > Flashcards

Colour Doppler Flashcards

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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
Q

what colour is shown is what type of display parameter

A

hue

26
Q

brightness is what type of display parameter

A

luminance

27
Q

what is saturation

A

amount of a colour

28
Q

wall filter

A

gets rid of clutter, eliminates lower frequency doppler shift caused by tissue motion

29
Q

what happens if you increase PRF too much to get rid of aliasing?

A

echo misplacement

30
Q

true or false - you can use aliasing to your advantage in stenosis

A

true - highlights areas of highest velocity

31
Q

priority

A

greyscale vs colour threshold - echoes below cut off amplitude will show as colour. Stronger echoes will be grey scale

32
Q

in priority, echoes below cut-off amplitude will show as what? and echoes above cut-off amplitue will show as

A

below cut off amplitude = colour

above cut off amplitude = greyscale

33
Q

Limitations to colour doppler (5)

A
  1. sonographer skill
  2. body type
  3. aliasing
  4. Angle dependence
  5. Tortuous vessels may look like flow reversal or aliasing
34
Q

power doppler displays

A

related to amplitude / concentration of RBC

35
Q

what is the only thing power doppler displays do?

A

only shows presence of flow

36
Q

advantages of power doppler (4)

A 
independent of doppler shift 
independent of doppler angle
no aliasing (same as CW)
improved sensitivity (deeper penetration, smaller vessels, slower flows)
37
Q

disadvantages of power doppler

A

no directional information
no flow speed information
no flow character information

Physics (9 decks)

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