Imaging of the ischaemic penumbra with a particular diffusion-weighted imaging (DWI)/ perfusion-weighted imaging (PWI) mismatch is a promising approach to the selection of patients with acute ischaemic stroke for trials of intervention. The investigators want to apply multimodal resonance imaging methods such as functional magnetic resonance imaging ( fMRI), diffusion tensor imaging (DTI), arterial spin labeling (ASL) to guide treatment and predict the prognosis of stroke.