The Transcranial Doppler (TCD) and the more recent Transcranial Color Doppler (TCCD) are tests that measure the velocity of blood flow through the brain's blood vessels. Used to help in the diagnosis of emboli, stenosis, vasospasm from a subarachnoid hemorrhage (bleeding from a ruptured aneurysm), and other problems, this relatively quick and inexpensive test is growing in popularity in the United States. TCD is effective to detect sickle cell disease, (in order) established for ischemic cerebrovascular disease, subarachnoid hemorrhage, arteriovenous malformations and cerebral circulatory arrest and possibly useful for perioperative monitoring and menigeal infection. The equipment used for these tests is becoming increasingly portable, making it possible for a clinician to travel to a hospital, doctor's office or nursing home for both inpatient and outpatient studies. It is often used in conjunction with other tests such as MRI, MRA, carotid duplex ultrasound and CT scans.