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C2 > Applications of ultrasound Doppler > Flashcards

Applications of ultrasound Doppler Flashcards

1
Q

what is the doppler effect used for

A

to measure speed of blood

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2
Q

how does the doppler effect measure blood speed

A

ultrasound doppler shift measured by comparing transmitted and received ultrasound signals (usually pulses)
spectral - at a single location
over a region - colour/power

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3
Q

what is doppler shift proportional to

A

blood speed for a fixed angle between artety (direction of flow) and ultrasound beam direction

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4
Q

what does the colour map show on the colour doppler image

A

colour map
tens of cm per second
blood flow colour coded to direction relative to ultrasound waves
switch on ultrasound machine where you can switch between 2
might change setting so blood flow appears in shade red and veins (where blood flows in opposite direction) are shades of blue/green

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5
Q

what can the spectral doppler trace tell you

A

measuring speed of blood at a particular point within middle of arery
measuring along the direction on pic above
line is angled in postion of artery

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6
Q

what does ECG tell you

A

heart rate of patient
increases in speed of blood are short time after we get a heartbeat
this delay is the time it takes for the pulse wave that travels within the blood from the heart to the particular artery

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7
Q

where is the transducer placed

A

placed on skin, sending out ultrasound pulses parallel to the white line

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8
Q

what does the depth on the colour imaging measure

A

measure blood flow between 1 and 2cm

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9
Q

what does the spectral doppler trace measure

A

generally measure blood velocity that corresponds to blue line which is the envelope - maximum velocity of speed that’s being measured

spread of speed within small sample volumes that is spectral broadening shape

take max blood velocity

how speed of blood varies in time at a particular point in a blood vessel

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10
Q

what is theta best for Doppler shift

A

< 60 and fixed

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11
Q

how are signals from vessel walls filtered out and what is the amplitude

A

filtered using a wall filter and signal from vessel wall has high amplitude and low Doppler shifts

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12
Q

what are types of Doppler ultrasound device

A

continuous wave - measures velocities over a wide range of depths

pulsed wave - gated to measure veloctity at a particular depth. pulse repetition frequency determines max velocity that can be measured

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13
Q

what types of Doppler imaging are there

A

Colour Doppler - colour= velocity + direction

Power Doppler - colour = strength of Doppler signal (has no speed info encoded in it)

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14
Q

what are colour Doppler artefacts

A

noise/flash due to tissue movement or by movement of probe
aliasing due to incorrect system PRF settings - due to incorrect setting can cause light blue regions within red (artefact)
high speeds are being mapped as low speeds in opp direction

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15
Q

what is represented on power doppler

A

pixel colour represents the power = amp squared of the received doppler signal.

colour independent of blood vessel representation

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16
Q

what are advantages of power Doppler

A

relative independence to vessel orientation
sensitivity to low blood flow
useful for visualising complex vascular geometries

17
Q

what are clinical applications of extracranial

A

assessment of carotid atherosclerotic stenosis
arterial dissection (car accidents, stabbings etc.)
carotid body and head and neck tumours

18
Q

what are clinical applications of intracranial

A

assessment of arterial stenoiss
evaluation of collateral flow and arterial malformations
aneurysm detection
investigation of dynamic cerebrovascular response
embolus detection
intraoperative monitoring

19
Q

what is a common site for carotid atherosclerosis

A

carotid bifurcation

20
Q

what is the pathology of carotid

A

lumen of artery is narrowed (stenosed)

plaques may become unstable, rupture and produce emboli leading to brain infarction

21
Q

what is the clinical importance of assessing carotid stenosis

what are the problems

A

risk factor for stroke and TIA
one indication for carotid endarterectomy

several different definitions of stenosis, little standardisation

22
Q

what are some randomised controlled trials for carotid surgery

A

NASCET - 1 major stroke prevented for 6 patients treated if degree of stenosis is 70-99%

ECST - 80% stenosis

ACST - high grade stenosis may benefit from surgery

23
Q

what are disadvantages of using xray/ct/mra

A

invasive, a contrast agen is usually required
only lumen is visualised
ionising radiation dose in case of xray or CT
3D diagnostic scanners not portable in general, expensive

2D, vessel diameter measurements highly dependent on the projection plane

24
Q

what are advantages of Doppler ultrasound

A 
low cost equipment
portable
real time imaging
can see vessel wall and blood
multimodal
25
Q

what are the methods of carotid stenosis measurement using Doppler

A
  • direct measurements from transverse images

- measure velocity

26
Q

what are the principles of Doppler-based methods

A

velocity increases with degree of stenosis

relate velocity to stenosis

27
Q

in spectral Doppler, where do you measure velocity

A

at site of maximal stenosis

28
Q

what are problems with doppler based stenosis estimation

A

large variability in blood velocity, reference measurement

errors in velocity measurements

29
Q

where in brain does ultrasound pass through with transcranial Doppler

A

temporal window, occipital or eye

30
Q

how does the transcranial Doppler ultrasound work

A

measurement of cerebral blood velocities
low frequency vs diagnostic ultrasound
access via temporal (mca–>circle of willis) or occipital (basilar arteries) windows or eye

31
Q

what is tcd ultrasound used to detect and why it useful

A

stenosis, aneurysm, vasospasm, embolus detection

useful for monitoring neurovascular surgical procedures

32
Q

what are the advantages of tcd

A

low-cost
portable
real time velocity monitoring
no contrast agent

33
Q

what are limitations of tcd

A

access to limited sites due to limited no. of windows because of bones

doppler angle can’t be estimated accurately
vessel determined by velocity waveform characteristics

poor resolution as low frequency ultrasound

34
Q

what do we see with intraoperative TCD monitoring and what can it indicate

A

see MCA
indicates velocity changes, emboli, kinking of shunt, poor air seal.
can determine co-lateral blood flow and see shunt insertion

C2 (24 decks)

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