Brain infarction can be detected by CT. This is because in the ultra-early and early stages of cerebral infarction, the brain tissue at the lesion site is not yet completely necrotic, and there is still an ischemic semi-dark zone around the core infarct area, and the brain tissue that is not yet completely necrotic may not appear as a low-density shadow on CT. Therefore, the golden time to save the brain tissue on the verge of necrosis is during the time when the low-density shadow of brain infarction has not appeared on CT. By means of intravenous thrombolysis, antiplatelet aggregation and endovascular therapy, the ischemic semidark zone can be salvaged, thus allowing partial recovery of neurological function in patients with cerebral infarction. If the patient’s cranial CT has seen hypointense shadow, it means that the brain tissue is basically necrotic and there is no ischemic semidark zone, then intravenous thrombolysis and endovascular treatment cannot be performed.