Applications of ultrasound Doppler Flashcards
what is the doppler effect used for
to measure speed of blood
how does the doppler effect measure blood speed
ultrasound doppler shift measured by comparing transmitted and received ultrasound signals (usually pulses)
spectral - at a single location
over a region - colour/power
what is doppler shift proportional to
blood speed for a fixed angle between artety (direction of flow) and ultrasound beam direction
what does the colour map show on the colour doppler image
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
what can the spectral doppler trace tell you
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
what does ECG tell you
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
where is the transducer placed
placed on skin, sending out ultrasound pulses parallel to the white line
what does the depth on the colour imaging measure
measure blood flow between 1 and 2cm
what does the spectral doppler trace measure
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
what is theta best for Doppler shift
< 60 and fixed
how are signals from vessel walls filtered out and what is the amplitude
filtered using a wall filter and signal from vessel wall has high amplitude and low Doppler shifts
what are types of Doppler ultrasound device
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
what types of Doppler imaging are there
Colour Doppler - colour= velocity + direction
Power Doppler - colour = strength of Doppler signal (has no speed info encoded in it)
what are colour Doppler artefacts
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
what is represented on power doppler
pixel colour represents the power = amp squared of the received doppler signal.
colour independent of blood vessel representation
what are advantages of power Doppler
relative independence to vessel orientation
sensitivity to low blood flow
useful for visualising complex vascular geometries
what are clinical applications of extracranial
assessment of carotid atherosclerotic stenosis
arterial dissection (car accidents, stabbings etc.)
carotid body and head and neck tumours
what are clinical applications of intracranial
assessment of arterial stenoiss
evaluation of collateral flow and arterial malformations
aneurysm detection
investigation of dynamic cerebrovascular response
embolus detection
intraoperative monitoring
what is a common site for carotid atherosclerosis
carotid bifurcation
what is the pathology of carotid
lumen of artery is narrowed (stenosed)
plaques may become unstable, rupture and produce emboli leading to brain infarction
what is the clinical importance of assessing carotid stenosis
what are the problems
risk factor for stroke and TIA
one indication for carotid endarterectomy
several different definitions of stenosis, little standardisation
what are some randomised controlled trials for carotid surgery
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
what are disadvantages of using xray/ct/mra
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
what are advantages of Doppler ultrasound
low cost equipment portable real time imaging can see vessel wall and blood multimodal
what are the methods of carotid stenosis measurement using Doppler
- direct measurements from transverse images
- measure velocity
what are the principles of Doppler-based methods
velocity increases with degree of stenosis
relate velocity to stenosis
in spectral Doppler, where do you measure velocity
at site of maximal stenosis
what are problems with doppler based stenosis estimation
large variability in blood velocity, reference measurement
errors in velocity measurements
where in brain does ultrasound pass through with transcranial Doppler
temporal window, occipital or eye
how does the transcranial Doppler ultrasound work
measurement of cerebral blood velocities
low frequency vs diagnostic ultrasound
access via temporal (mca–>circle of willis) or occipital (basilar arteries) windows or eye
what is tcd ultrasound used to detect and why it useful
stenosis, aneurysm, vasospasm, embolus detection
useful for monitoring neurovascular surgical procedures
what are the advantages of tcd
low-cost
portable
real time velocity monitoring
no contrast agent
what are limitations of tcd
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
what do we see with intraoperative TCD monitoring and what can it indicate
see MCA
indicates velocity changes, emboli, kinking of shunt, poor air seal.
can determine co-lateral blood flow and see shunt insertion
