Transcranial Doppler

Transcranial Doppler (TCD) is a non-invasive ultrasound method used to measure the velocity of blood flow through the brain's blood vessels. TCD uses a low-frequency transducer, usually in the range of 2 MHz, which is placed on the scalp above the window of the skull.

History

The technique was first introduced by Rune Aaslid in the 1980s. Aaslid was working with neurosurgeons at the University of Iowa when he developed the technique.

Technique

The TCD technique involves the use of a Doppler probe that emits an ultrasound beam. This beam is reflected off the moving blood cells within the cerebral arteries and is then picked up by the probe. The frequency shift (Doppler shift) of the reflected ultrasound is proportional to the speed of the blood cells, allowing the velocity of blood flow to be calculated.

Clinical Applications

TCD is used in a variety of clinical settings, including the diagnosis and monitoring of stroke, sickle cell disease, subarachnoid hemorrhage, and brain death. It is also used in research settings to study cerebral hemodynamics.

Advantages and Limitations

The main advantage of TCD is that it is non-invasive and can be performed at the bedside. It provides real-time information about blood flow velocity in the major cerebral arteries. However, its use is limited by the need for a suitable acoustic window, which is not present in all individuals. Furthermore, it provides information about blood flow velocity rather than volume, and it is unable to provide information about smaller vessels.

See Also

• Ultrasound
• Doppler effect
• Stroke
• Sickle cell disease
• Subarachnoid hemorrhage
• Brain death