Transcranial Doppler (TCD) is an older technology that has been recently redefined to be of great use. This is a painless test in which the technician will use an ultrasound and gel to assess the arteries of the brain. The test takes anywhere from 30-50 minutes. It is noninvasive and simply measures blood flow in the arteries of the brain. TCD is used to check for narrowing, spasms, or even blockages of the arteries within the brain. You do not need to take any special measures to prepare for this test. The ultrasound will be placed on your skin in four areas: the sides of the head over the temples, under the chin, over the closed eye, at the back of the neck. Following the test you may resume your normal daily activities as you had planned. After the study is done, the physician will later discuss all the results with you.