In acute cerebral infarction, cytotoxic edema leads to reduced diffusion and decreased ADC values, which appear as high signal on diffusion-weighted images. In the subacute stage, especially in the early subacute stage, the infarct foci may appear with varying degrees of high signal on DWI images due to T2 prolongation and increased proton density; in the late subacute stage, the foci show various expressions on ADC images, which can be slightly low, equal or high signal, with a wide range of variability in ADC values, which may lead to diagnostic false negatives on DWI or ADC maps at this time. Late infarct foci with softening foci form, with low signal on DWI and increased ADC values. Advantages of DWI in the diagnosis of cerebral infarction: 1. Ultra-early diagnosis: it can detect infarct foci earlier than 6h. 2.It can help to detect micro lesions. 3.It can identify fresh or old infarct foci. 4.Short scanning time, can be only a few tens of seconds, suitable for emergency patients who are not easy to cooperate with the examination. 5.Help to make differential diagnosis with other lesions.