Transcranial Doppler and color-coded duplex sonography: Established and new applications

Transcranial Doppler and color-coded duplex sonography provide reliable information on cross-flow through the circle of Willis, stenoses, occlusions and vasospasm of the major basal cerebral arteries. The CO2 and acetazolamide tests allow quantitative evaluation of the hemodynamic impact of obstructive cerebrovascular disease. Furthermore, transcranial Doppler sonography is used for detection of enhanced intracranial pressure, confirmation of brain death, detection of cerebral microemboli (,,high intensity transient signals'' = ,,HITS''), and patent foramen ovate. In the future, cerebral microemboli may become a marker for embolic activity of both occlusive carotid artery and cardiac disease. Transcranial color-coded duplex sonography identifies intracranial hemorrhage, cerebrovascular malformations, and hydrocephalus, but is inferior to neuroradiological techniques. Transpulmonary contrast agents make the examination of patients with inadequate insonation windows feasible, and increase diagnostic confidence in transcranial ultrasonography. Transcranial power-based color-coded duplex sonography (,,power Doppier'') may further improve transcranial ultrasonography, and visualize flow in smaller vessels.