A TCD uses ultrasound waves to measure the blood flow rate and direction in the mail cerebral arteries of the brain. It helps detect blockages, narrowing, or spasms of the arteries. TCD is non-invasive and has no risks.
No special precautions are necessary. No special preparation is needed. There are not diet or activity restrictions before the test. The patient may remove their contact lenses and may wish to avoid use of make up, since the gel is likely to smear it.
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 least 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.