TCD is short for Transcranial Doppler. Transcranial Doppler ultrasound results look at the blood flow rate, beat-to-beat index, and direction of blood flow to assess cerebrovascular function as well as lesions. 1. Blood flow rate: Blood vessels have their own normal flow rate. If the blood flow rate is too fast or too slow, it is abnormal, which indicates that there are abnormalities in the blood vessels. Fast blood flow may be due to spasm or narrowing of blood vessels, while slow blood flow may be due to insufficient blood supply to the brain. 2. pulsatility index: the current elasticity of blood vessels can be assessed by the pulsatility index of blood vessels. If the pulsatility index of blood vessels is too high, it is often considered that the elasticity of blood vessels is reduced, which may be the manifestation of atherosclerosis. 3. Direction of blood flow: If there is an abnormality in the direction of blood flow, it is very likely that the patient is suffering from blood theft, for example, blood theft from the subclavian artery. The results of transcranial Doppler ultrasound examination are difficult to be understood by non-specialists, and it is recommended that the results of the examination be sent to the doctor for analysis in a timely manner so as to assist in the diagnosis.