Previous research has shown there wasn't inevitable relationship between mismatch area and infarct growth according to Volumetric-subtraction mismatch volume.The recently published on Stroke paper has proposed Coregistration mismatch to calculate the mismatch to replace ischaemic penumbra, and it reignites hope for clinical application of the PWI/DWI mismatch. But the correlation between the mismatch, calculated by Coregistration mismatch method,and the clinical outcome of the patients with acute ischemic stroke is still unknown. so the investigators plan to conduct a prospective observational cohort study.

NIHSS,mRS and MR PWI/DWI/MRA are performed within 48 hours of stroke onset and final MR T2/flair image at ≈1 month. And then,Volumetric-subtraction mismatch and Coregistered mismatch will be calculated,respectively.finally,we will assess and compare the Volumetric-subtraction mismatch and Coregistered mismatch, and to clarify which method match the clinical outcome more better.

Inclusion Criteria:

• Aged eighteen or above
• Acute middle cerebral artery ischemic stroke
• Stroke onset within 48 hours
• Included a complete set of initial MR images and final outcome MR images up to 1 months

Exclusion Criteria:

• History of stroke in the past 6 weeks
• Pre-existing neurological or psychiatric disease that could confound the study results such as a pre-stroke mRS score greater than 3
• CT evidence of the following conditions before enrollment:

Significant mass effect with midline shift Evidence of intracranial hemorrhage

• With contraindication to MR such as severe allergy to contrast media

Patients with acute ischaemic stroke admitted to ASU.