Introduction
Transcranial Doppler (TCD) was developed in the late 1970s by Rune Aaslid and was first introduced clinically in 1982. TCD enables a non-invasive investigation of intracranial cerebral haemodynamics in a variety of conditions including subarachnoid haemorrhage, acute stroke, and intracranial and extracranial vascular stenosis. TCD has also been used for monitoring cerebral haemodynamics during carotid and cardiopulmonary bypass procedures, and also for the assessment of brain death. More recently TCD has been used for the detection and monitoring of cerebral emboli in acute stroke and TIA (particularly in patients with a potential cardiac source of emboli eg. Atrial fibrillation), and post-operatively after carotid endarterectomy.

Conclusion
Transcranial Doppler is an important non-invasive adjunct in the evaluation and management of patients with cerebrovascular disease. It allows non-invasive assessment of the anatomy and haemodynamic status of the cerebral circulation in a variety of neurological conditions as well as allowing assessment of the potential risk for embolic stroke.

The inability to directly visualize blood vessels has, at least partially, limited its use, however, the use of echo contrast agents and the advent of transcranial colour duplex sonography has significantly enhanced the utility of this non-invasive technique.