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Signal change on MRI after stroke

                            Signal change on MRI after acute stroke


Signal change Time it takes to become abnormal after stroke Time it takes to become normal after stroke Notes


DWI high signal


2-4 hours 10-14 days DWI study sometime is quite variable for lacunar or posterior circulation infarction.


ADC low signal


2 minutes 7 days  


FLAIR high signal


from 6 hours   Sometimes arterial hyperintensity starts on FLAIR within the first two hours.



Cortical laminar necrosis with T1 high signal


from 3-5 days, usually after 2 weeks after 3 months No high signal on GRE.


Arterial enhancement


0-2 hour, commonly after 3 days 1 week  


Meningeal enhancement


1-3 days 1 week Only after large stroke.
Parenchymal enhancement 1 day, usually after 3 days 2 months If persistent beyond 3 months, think other processes. Gyriform in cortical stroke and generalized/ringlike in lacunar, basal ganglia, brain stem or venous infarction. Lacunar infarctions have more interse enhancement. Enhancement within first 6 hours increases the risk of hemorrhagic transformation.


Parenchymal enhancement after incomplete infarction


2-4 hour 2 days Good prognosis
Hemorrhagic transformation most common after 24 to 48 hours rarely after 1 week Petechial microbleeding can happen earlier and is of no importance and not contraindication for TPA.