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Physics > Spectral Doppler Displays > Flashcards

Spectral Doppler Displays Flashcards

1
Q

spectral doppler aka

A

pulsed wave

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2
Q

how many scan lines in spectral doppler

A

firing along a single scan line (versus colour doppler which fires 3-32 pulses per scan line, 10-20)

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3
Q

how many cycles per pulse in doppler

A

5-30 cycles per pulse

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4
Q

pulsed wave doppler systems provide the ability to ___

A

select depth from which doppler info is received (CW cannot do this)

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5
Q

range gating

A

ability to select info from a specific depth along beam

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6
Q

what does range gating enable (2)

A

depth sensitivity and a small sample volume

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7
Q

sample volume

A

specific area being assessed “gate”

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8
Q

what is an effective sample length? sample width?

A

sample length = 1/2 SPL + gate length

sample width = beam width

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9
Q

spectral doppler detects (4) of blood flow

A 
same as colour :
presence
speed
character 
direction
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10
Q

spectral doppler allows for quantification of blood flow- true or false

A

true

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11
Q

what is on the x and y axis of spectral doppler

A

x - time

y - doppler shift or velocity

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12
Q

bidirectional doppler what and where

A

detects positive and negative shifts IN THE doppler-shift detector/ quadrature phase detector

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13
Q

what is fast fourier transform and WHERE

A

within spectrum analyzer
Determines frequency spectrum
Determines each doppler shift frequency (x) and its strength (y)
converts voltage over time to amplitude over frequency

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14
Q

each point of a spectral waveform shows (3)

A

direction (+/-)
magnitude (how fast)
amplitude (brightness)

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15
Q

what factors affect direction? (2)

A

coming away/towards transducer

direction of steering

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16
Q

what factors affect magnitude? (2)

A 
speed of blood flow (e.g. within stenosis)
doppler angle (larger angle, smaller cosine, smaller Doppler shift, larger calculated velocity)

Without angle correct, it is a slower calculated velocity -therefore UNDERESTIMATES velocity with a 0 angle

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17
Q

what factors affect amplitude? (3)

A

intensity of returning echo

  • concentration of RBCs
  • reflectors
  • impedences
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18
Q

gate size/sample volume affects

A

range resolution

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19
Q

what is the opposite of range resolution

A

range ambuiguity

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20
Q

gain

A

amplification of incoming echoes voltages

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21
Q

invert

A

arteries + above BL,

veins - below BL

22
Q

if you want more positive signals, do what?

A

move baseline down

23
Q

wall filter

A

gets rid of clutter, cuts off slower/low frequency flows

24
Q

what affects the scale?

A

PRF

25
Q

increase PRF and what happens to the scale

A

increases

26
Q

if you decrease PRF too much what happens

A

aliasing

27
Q

what happens if you increase PRF too much?

A

shows faster flow speeds but can produce a poor signal because of wasted space

28
Q

if you don’t correct the angle, will the speed be underestimated or or over estimated?

A

underestimated because increasing the angle:
increases the speed
decreases doppler shift

29
Q

true/false - arteries are phasic and lower velocity wave form

A

FALSE thats veins

arteries are pulsatile and higher velocity waveform

30
Q

high resistance flow seen in

A

external carotid artery

extremities

31
Q

low resistance flow seen in

A

internal carotid artery, common carotid artery, blood hungry organs

32
Q

factors that characterize a stenosis (4)

A
  1. decreased area increased velocity
  2. turbulence (if surpassed reynolds number)
  3. potential for aliasing
  4. spectral broadening
33
Q

what is spectral broadening

A

caused by turbulent flow where theres a greater variation in the velocities, causing vertical thickening of the spectral trace
narrowing of window

34
Q

spectral broadening can be produced artificially (3)

A

increased gain
increased sample size
beam spreading with wide aperture arrays

35
Q

what waveforms suggest a proximal stenosis (2)

A

upstream, pre-stenosis
tardus parvus waveform
monophasic waveform

36
Q

tardus parvus waveform

A

pre-stenosis waveform that is very slow and rounded

37
Q

what may suggest a distal stenosis?

A

increased resistance

38
Q

if the ICA waveform (recall low resistance) looks like the ECA wavefirm (recall high resistance) what can this suggest?

A

distal stenosis

39
Q

quantitative index

A

acceleration time

40
Q

what does quantatative index show

A

tardus parvus

41
Q

spectral limitations (5)

A
  1. sonographer skill
  2. body type
  3. aliasing
  4. movement
  5. range gated to specific depth
42
Q

how can you fix aliasing (4)

A
  1. adjust baseline
  2. lower operational frequency
  3. increase doppler angle
  4. increase PRF
43
Q

spectral doppler is continuous wave and pulsed wave

A

true

44
Q

what is the sample volume like in CW

A

LARGE overlapping sample volume (due to two transducer elements)

45
Q

what is the limitation to CW

A

range ambiguity (poor range resolution) PW has great range resolution

46
Q

benefit to CW

A

CW cannot alias because there’s no PRF in CW

can pickup very high max values without aliasing

47
Q

what type of doppler shows perfusion?

A

power

48
Q

what type of doppler shows quantitative?

A

spectral

49
Q

what type of doppler shows global

A

doppler shift and doppler power

50
Q

Without angle correct, will calculated velocity be higher or lower?

A

Lower

Cos0 = 1
Cos60 = 0.5

Increasing the angle puts a fraction in the denominator of the velocity equation, increasing the calculated value

Physics (9 decks)

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