Transcranial Doppler ultrasound is a medical imaging study which is designed to provide information about the health of the blood vessels inside the brain. Using this imaging study, a doctor can identify risk factors, learn more about an ongoing condition involving the brain, or follow up on the results of a surgical procedure. TCD, as it is also known, may be used on its own as a standalone diagnostic test, or as part of an array of tests which are intended to provide a more complete picture of a patient's case.
The procedure takes around 20 to 30 minutes, and can be performed by an ultrasound technician or radiologist. A small amount of gel is applied around the skull, often near the base of the skull or by the ears, and an ultrasound probe is gently pressed against the skin. During the test, the patient can remain fully clothed and conscious, and does not need to take any special preparations. The patient is usually asked not to talk to avoid jostling the head and disrupting the results. After the transcranial Doppler ultrasound is read by a radiologist, the results can be discussed with the patient.
This ultrasonography technique relies on a phenomenon known as the Doppler effect, characterized by shifts in pitch which occur as objects move away from or closer to the observer. Regular ultrasound simply bounces soundwaves off the inside of the body to generate an image, while Doppler ultrasound measures changes in pitch and uses those to construct an image of movement inside the body. This allows people to trace the flow of blood through various blood vessels by watching it move on the ultrasound screen.
During the transcranial Doppler ultrasound study, the images will be displayed in real time. The device often color codes them for convenience, showing the direction and velocity of bloodflow. Some machines also map out physical structures in the region to create a frame of reference, while others just show the blood vessels caught by the ultrasound probe.
A transcranial Doppler ultrasound can be used to look for signs of stenosis or aneurysm in the brain, and to check for clots, bleeds, and similar problems. Neurosurgeons may also use transcranial Doppler ultrasound during surgery as a monitoring tool to keep an eye on the patient's brain. This imaging technique allows people to identify problems in the early stages, creating an opportunity for early intervention which can minimize damage to the brain.