TCD is the abbreviation of Brain Doppler, which is mainly used to check the condition of blood vessels in the skull. The TCD report can assess the condition of blood vessels through the following aspects: 1) Blood flow rate, each blood vessel has its own normal blood flow rate, and when the blood flow rate is too slow or too fast, it suggests that the blood vessels are abnormal. 2) The beat-to-beat index can be used to assess the elasticity of the vessels, as well as the arterioles of the vessels if they are too slow. When the blood flow rate is too slow or too fast, it suggests that the blood vessels have abnormalities. Fast blood flow rate can be seen in stenosis or vasospasm, and if the blood flow rate of the blood vessels is too slow, it is considered that the patient has chronic cerebral insufficiency of blood supply.2. The elasticity of the blood vessels and the degree of atherosclerosis of the blood vessels can be assessed by the pulsatility index, and the patients’ atherosclerosis can be considered to have atherosclerosis when the pulsatility index of the blood vessels is increased. If the direction of blood flow is abnormal, it can be considered that the patient has the possibility of blood stealing, and the common clinical cases include subclavian artery blood stealing.