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
