Brain ultrasound can be used to determine the location of stenosis or occlusion of blood vessels and assist in the diagnosis of cerebral infarction, while the most important diagnostic methods for cerebral infarction are CT examination and diffusion-weighted MRI examination and so on. Cerebral color ultrasound, also known as transcranial Doppler ultrasound (TCD), is mainly used to examine intracerebral blood vessels through the weak parts of the skull, and can determine whether there is stenosis or occlusion of arteries, the location of occlusion or stenosis of blood vessels in cerebral infarction, evaluate the cerebral collateral circulation of ischemic localization, and monitor the situation of vascular recirculation in real time, etc. It is recommended that the people who have acute ischemic stroke undergo the TCD examination as early as possible. For people with cerebral infarction, CT examination should be performed first, which can exclude cerebral hemorrhage, intra- and extradural hematoma, etc. In 6~12 hours after cerebral infarction, moderate to large cerebral infarction can be seen in CT examination; and diffusion-weighted MRI examination should be performed as soon as possible, which has diagnostic significance for early ischemic infarction foci in the brain.