The cranial DWI examination is a type of MRI examination, and the Chinese name is called diffusion-weighted imaging examination. The basis of DWI signal change in cerebral infarction is brain cell swelling that can occur minutes after the infarction, leading to cytotoxic edema, and diffusion imaging shows abnormally high signal shadow, called diffusion restriction, suggesting new cerebral infarction. It is significantly better than cranial CT and MRI plain T1 and T2 phases for confirming the diagnosis in patients with acute cerebral infarction, and is more sensitive to hyperacute phase lesions, and can detect abnormal high signal in cerebral infarct lesions as early as 2 hours after the onset of disease. However, it should be noted that the absence of diffusion high signal shadowing does not exclude the possibility of cerebral infarction, and about 2%-7% of patients with cerebral infarction have negative diffusion imaging performance due to the absence of diffusion imaging changes after very small lacunar cerebral infarction, brainstem infarction, embolus lysis, and revascularization. Diffusion imaging high signal gradually decreases at 1-2 weeks, while in chronic phase cerebral infarction at 3 weeks-3 months, diffusion imaging can show isosignal or low signal shadow.