Perfusion, Diffusion and SWI Flashcards
What are the Acute Ischaemic Stroke Pathophysiology?
- Flow abnormalities
- Monovascular level: large vessel occlusion
- Microvascular level: Reduced tissue perfusion - Cellular dysfunction
- flow 10-15ml/100g/min
- swelling of neurons: cytotoxic oedema - Structural breakdown (after 6 hours)
- damage to BBB
- fluid leaks into extracellular space: vasogenic oedema
What are the sequences for Hyperacute Stroke?
- DWI
- T2*/SWI
- FLAIR
- MRA
- MR Perfusion?
DWI
if there is cytotoxic oedema and the neurons swell, bottom moves much more difficult in the extracellular space –> restricted diffusion
Restricted diffusion
Appears bright on DWI
Appears dark on ADC map
What are features of DWI?
- Highly sensitive to acute ischaemia
- DWI lesion not always irreversible
- DWI lesion volume good prognostic indicators of:
- risk of haemorrhagic transformation
- risk of malignant MCA infarction
- 90 days FLAIR infarct volume (24h DWI) - DWI changes in haemorrhage
What is ADC map a true measure of?
Water movement
What is important to do?
Distinguish acute from chronic infarcts
Acute infarct
DWI: bright
ADC: dark
Chronic infarct
DWI: dark
ADC: bright
What can be observed on a CT?
Acute stroke will not appear so dark
What happens if you have stroke on 2 different territories?
Think of embolic or vasculitis
What is vasculitis?
Inflammation of the blood vessels
How do you predict the malignant MCA infarction?
- Whether DWI volume was greater than 82 ml
- Whether there was a clinical scale NHIS
- Whether there was an occlusion in the mamogram
DWI-FLAIR Mismatch
If the FLAIR becomes positive - likely to be older than 4.5 hours
if the FLAIR is largely negative - a very recent infarct
what are the features of oedema in the acute stroke?
- Cytotoxic
- Cellular swelling
- Restricted diffusion
- if older - Vasogenic odema
- Restricted diffusion - a week to 10 days - normalizes
What is PWI good for?
Looking at hyperacute stroke
Directly looking at the blood flow
How can you look at the blood flow?
- Inject a contrast medium
- CT iodinated
- MR gadolinium - Take rapid series of images
- Look at time sequences on intensity curve
What is Arterial Spin Labelling?
- Doesn’t need an injection of a contrast medium
- Labels endogenous hydrogen molecules in carotid arteries
- Look at how quickly spins recover
- Measure perfusion
What is the pnemumbra?
Tissue that is endangered but not infarcted yet
MR perfusion
Inject gadolinium
First pass: Gadolinium goes to the brain - expect a signal drop
What is the Central Volume Theorem?
- Height of the bolus corresponds to the CBF
- Area under the curve is the CBV
- MTT - is the area divided by the height
What is the equation for the Central Volume Theorem?
MTT = CBV/CBF
CBF = CBV/MTT
How can you increase the blood volume?
- Vasodilation
2. Collaterals
What does the convolution method give?
Gives the correct CBF
Select an input function
PWI to extend time window
Tmax of > 6 seconds
Infarct size < 70 ml
Perfusion lesion/infarct vol > 1.8
Benefit from stroke treatment
What do you look for in the mismatch?
Tissue where the blood takes longer to arrive than usual
TIA
Do not show diffusion abnormality
Resolves within 24 hours
Patients with TIA symptoms
If diffusion was abnormal - 2 patterns:
- Increase in Tmax - takes longer for the blood to arrive
- Cerebral blood flow was normal
- There is vasodilation/some collaterals
What is Crossed Cerebellar Diaschisis (CCD)
If you have abnormality or hyperperfusion in one of the cerebral hemispheres - contralateral cerebral hemisphere - complicated neurogenic depression mechanism
What is Moyamoya disease?
Non vasculitic, non-artherosclerosis occlusion of the terminal carotids
- No inflammation
- Ideopathic
What is EC-IC Bypass?
A surgical procedure to increase cerebral blood flow
What are the 2 mechanisms of stroke?
- Embolic - abnormalities in DWI
2. Haemodynamic
What is Deoxyhaemoglobin?
Paramagnetic
