Slowed arterial blood flow is mostly mentioned in transcranial Doppler reports. Blood flow velocity refers to the speed of red blood cells flowing in the blood vessels and is correlated with the size of the vessel diameter as well as the distal resistance and proximal pressure of the vessels. The most common cause of slowed arterial blood flow in the Doppler test report is the patient’s blood viscosity, and the patient will have the manifestation of chronic lack of oxygen in brain cells, which can lead to dizziness and dullness, and in severe cases, memory loss, etc. The middle cerebral artery is also detected through the temporal window. When the blood flow velocity of the middle cerebral artery is significantly lower than that of the anterior cerebral artery or the posterior cerebral artery, it indicates occlusion of the middle cerebral artery. The specificity of intracranial Doppler examination of vascular occlusion is not high, and only severe occlusion can have hemodynamic changes on Doppler.