Current Concepts of Cerebrovascular Disease Transcranial Doppler

Ultrasound examination of the extracranial carotid and vertebral arteries has been used for many years to diagnose and manage patients with cerebrovascular disease. However, evaluation of the intracranial circulation has until now required angiography. Extracranial ultrasound examinations utilize probe frequencies ranging from 3 to 10 MHz. These frequencies are unable to penetrate bone sufficiently to reflect signals from the intracranial arteries. Aaslid demonstrated that signals could be obtained from the middle cerebral artery (MCA) and anterior cerebral artery (ACA) with a 2-MHz probe directed intracranially from the temporal bone just above the zygomatic arch. The intracranial internal carotid artery (ICA), posterior cerebral artery (PCA), intracranial vertebral artery (VA), and basilar artery (BA) can also be insonated by the transcranial approach.