A TCD test uses ultrasound waves to measure the blood flow rate and direction in the main (cerebral) arteries of the brain. It helps detect blockages, narrowing or spasms of the arteries.
The test does not involve the use of needles or injections. TCD is done with either one or two probes placed against the skin. The examiner spreads a clear gel on the areas of the head where the probe will be placed:
- On each side of your head.
- Under your chin.
- Over your closed eyelid.
- At the back of your neck.
In these places, there is the last amount of thick protective bone and the sound waves can penetrate the best. The examiner adjusts the probe position and orientation to direct the sound waves toward the blood vessels of interest. Finding the best approach may take some time. A compression test may be performed during the exam. In this test, the main artery in the neck (carotid artery) is briefly compressed, and changes in blood flow patterns are observed. A full TCD exam may last 30-45 minutes, and often longer in patients with disease.
The gel is washed off with soap and water. No other after care is needed.