Carotid Imaging Flashcards
What are the 3 approaches to imaging?
anatomic criteria (degree of stenosis) morphological criteria (plaque characteristics) pathophysiological criteria (processes causing rupture)
what kind of imaging is used in anatomical criteria
Doppler and CT
who should have carotid imaging and when
all people with TIA or non-disabiling stroke within 7 days of event (NICE) or 24 hours (RCP)
how much percent was moderate disease present in men and women over 80
7.5% in men
5% in women
what are high risk plaque features
thin fibrous caps
intra-plaque haemorrhage
large lipid rich necrotic cores
neovascularisation
what do 3D TOF pulse sequences distinguish between
intact and thick vs thin and ruptured caps
what is preferred to use to see enhancement of fibrous tissue
contrast enhanced MRI
what does plaque haemorrhage do to the t1 signal
shortens the relaxation time of T1, resulting in bright signal on T1
what does haemorrhage degrade into in plaque haemorrhage
methaemoglobin
how can you image neovascularisation
use dynamic contrast enhanced MRI
or T1w using repeated measurement of contrast intensity
what does fibrous look like on: TOF T1 T2 PD STIR
TOF - isointense/hypointense T1 - isointense/hypointense T2 - hyperintense PD - isointense/hypointense STIR - hyperintense
what does lipid look like on: TOF T1 T2 PD STIR
TOF - isointense T1 - isointense/hyperintense T2 - hypointense PD - hyperintense STIR - hypointense
what is USPIO and what does it do to t2
Ultrasmall superparamagnetic particles of iron oxide enhanced MRI.
Particles taken up up by macrophages via scavenger receptors.
results in t2w susceptibility effect - reduced signal
what imaging can be used in pathophysiology
PET
what happens in PET generally
There is a proton-rich parent nuclues. Proton decays to neutron so positron and neutrino emitted. Positorn collides with ambient particles and loses kinetic energy. At thermal energies the positron combines with an electron to form an orbiting pair called positronium. About 10^-10s later, the positronium annihilates and 2 antiparallel 511 keV photons are produced.
in what plaques is FDG uptake higher in and what does it correlate with
higher in culprit plaques and those with high-risk plaque features
correlates with cardiovascular risk factors
what is FDG uptake associated with
associated with increased microembolic signals on transcranial Doppler. associated with increased risk of recurrent events
what is SUV and TBR and what are the equations
SUV - standardised uptake value = activity / (injected activity*weight)
TBR - tissue-to-background ratio = SUV in ROI / SUV in venous phase
what is a newer tracer other than FDG
Ga-DOTATATE targets somatostatin receptor subtype-2
what are the benefits of PET in research
highly sensitive
can directly measure effect of intervention on pathophysiology and is increasingly used in drug trials
what are the advantages of PET+MRI
combine morphology and pathophysiology
improved soft tissue contrast
reduced radiation
what are the disadvantages of PET+MRI
cost
availability
tolerability
attenuation correction
