Cranial Doppler, also known as transcranial Doppler, mainly uses ultrasound to check the condition of intracranial blood vessels through the skull, and can generally assess the general condition of blood vessels by measuring the blood flow velocity and the pulsatility index of blood vessels. 1. When intracranial Doppler does not measure the blood flow velocity or does not detect the blood flow, it can initially assess the presence of occlusion of intracranial vessels. 3. The main findings are abnormal blood flow velocity and direction of blood flow.4. Cranial Doppler can also detect whether the blood vessels are in spasm, which can be assessed by the changes in blood flow velocity and parameters during the examination, as well as the murmur of blood flow. For some patients with headache, cranial Doppler can also be used to monitor the passage of microemboli, etc.