Blood flow changes in cerebral atherosclerosis indicate a narrowing of a blood vessel in the brain. Cerebral blood flow is done by a brain ultrasound also known as a brain Doppler, which normally has a normal value for blood flow in each blood vessel. If cerebral blood flow is measured above this normal value, it indicates a narrowing of a blood vessel, possibly a stenosis, often in a single vessel. If all the vessels show increased cerebral blood flow, it means that the patient has increased blood flow in all of them, which may be caused by systemic diseases such as anemia or hyperthyroidism. If the cerebral blood flow is slowed, it is generally not clinically significant, so it depends mainly on whether the blood flow is increased in all or localized, and if it is increased in localized blood flow, further cerebrovascular examination is needed.