A Transcranial Doppler (TCD) study is a non-invasive test used to measure the velocity of blood flow through the vessels in the brain. It is helpful in the diagnosis of embolism, stenosis, ischemia, and hemorrhage. Restrictions in blood flow to the brain may lead to stroke.
In order to reduce the restriction of the ultrasound waves through the skull, areas where the skull walls are thinner are used for measurement. These areas include the temporal region above the cheekbone, over the closed eyelid, below the jaw and the back of the head.
The DVM-4300T Doppler Volume Flowmeter with the 2 MHz transcranial probe measures the blood flow velocity and graphs the velocity over time using spectral broadening. Changes in frequency are used to measure the velocity and direction of blood flow. The greater the change in frequency, the faster the blood is flowing through the arteries. The DVM-4300T produces 2-dimensional image of the TCD waveform for evaluation purposes.
The TCD exam can be combined with other tests to obtain information that can be used to locate restrictions in blood flow and/or track changes over time. |
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Interpreting the Results
TCD sound waves vary with the patient's heart rate as well as the direction and rate of flow. Each vessel has a specified flow direction. Flow rates may vary from person to person.
The absence of flow indicates a completely blocked vessel (However, the absence of signal may also be caused by the sound waves being blocked by the skull). Blood flowing in the opposite direction of normal flow, or alternating direction may indicate a blockage due to the blood being rerouted because of pressure abnormalities. Also, increased blood flow speed may indicate a partially blocked vessel or that blood is being rerouted from another vessel. |
