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. |