Early cerebral embolism is not visible on CT because only brain tissue is necrotic and the corresponding brain cells innervated by the cerebral arteries are necrotic, which can be seen on CT. Usually, it can be seen on CT imaging only after 24 hours. The diagnosis of cerebral embolism does not rely on CT alone, but also depends on the patient’s medical history and physical examination to make a decision, and if necessary, improve the head MRI to clarify the diagnosis.