Transcranial Doppler (TCD) ultrasound

What is transcranial Doppler ultrasound?

TCD is a noninvasive and painless ultrasound technique that uses sound waves to evaluate blood flow (blood circulation) in and around the brain. There is no special contrast or radiation involved in the test.

Physicians recommend this test to determine if there is anything happening in the blood vessels that is affecting blood flow to the brain. Transcranial Doppler ultrasound is often the test of choice for:

At Cedars-Sinai, TCD ultrasounds are used to evaluate the 13 major arteries supplying blood flow to the brain, but there are other TCD studies used to identify specialized problems related to brain blood flow:

  • Embolic detection monitoring
    This test detects any free-floating particles that may be in the bloodstream. These particles can be a significant source of stroke risk.
  • Agitated saline bubble study
    This test is specific for identifying whether there is a passageway or hole between the right and left chambers through which blood enters the heart. This hole usually closes after birth. If it doesn't close, it can be a source of increased stroke risk in certain patients.
  • CO2 vasomotor reactivity study
    This noninvasive study looks at whether the small vessels that regulate blood flow to the brain are working properly. When a small amount of carbon dioxide (CO2) and oxygen are inhaled, similar to holding one's breath, these small vessels should widen and increase blood flow to the brain. When a person hyperventilates, the vessels should shrink and slow blood flow to the brain.

Cedars-Sinai relies on transcranial Doppler expert Brenda Rinsky, RDMS.

What happens during a TCD at Cedars-Sinai?

During a TCD ultrasound, the patient lies on their back on a gurney. The technician applies a small amount of gel at the temples, over the closed eyelids, under the jaw and at the base of the neck.

Then the technician will place a small microphone-like device, known as a transducer, over those sites and listen to the blood flow. The transducer collects the sound waves and the computer uses those sound waves to create pictures that represent blood flow speed and resistance within the vessels.

Does the test cause any discomfort?

TCD ultrasounds are completely painless, and can be performed in any environment at Cedars-Sinai, including the:

  • Emergency Department
  • Inpatient rooms
  • Intensive care units (ICUs)
  • Operating rooms
  • Outpatient clinic

What preparations are needed before going in for a TCD?

There is no preparation necessary for the TCD ultrasound. However, it is important that the patient stay quiet and still during the test.

Since TCD includes sampling over the closed eyelid, patients should leave or remove hard contacts during the test. TCD will not be performed on patients who have had invasive eye surgery within the previous month, including laser sight correction, implants or cataract removal.

How long will the test last?

Depending on the type of measurement needed, the test lasts at least 45 minutes. Patients who are being tested as an outpatient should anticipate being at Cedars-Sinai for an hour and a half.

What happens after the test is complete?

For patients who are not currently admitted to the hospital, there are no restrictions following the exam and they may go home immediately. The patient’s neurologist will contact them with the results of the test.

For an appointment, a second opinion or more information, please call 1-800-CEDARS-1 (1-800-233-2771) or email us at