Transcranial Doppler ultrasound and brain MRI are two completely different tests and are not usually compared together. The former is mainly used to clarify the blood flow in the brain, such as whether there is a slowing down of blood vessel flow and narrowing of blood vessels, resulting in insufficient blood supply to the brain, and also to clarify the cause of cerebrovascular disease, whether there are vascular malformations, aneurysms, and whether there is microemboli rain formation. However, MRI is generally used to find out whether there are organic diseases in the brain, mainly to see whether there are lesions in the brain parenchyma, and can detect acute cerebral infarction, cerebral hemorrhage, brain tumor, encephalitis and other diseases. Also, if further MRI functional imaging and angiography are done, it can also help to clarify whether there are metabolic disorders in the brain and whether there are lesions in the cerebral blood vessels. General brain MRI imaging of the arterial system and venous system is more accurate than transcranial color Doppler ultrasound to look at blood vessels, but it does not help determine the presence of microembolic rain or help predict the incidence of cerebral infarction.