Transcranial Doppler ultrasound.

Transcranial Doppler ultrasound allows measurements of blood flow velocity to be made from the basal intracerebral vessels. The major advantages of transcranial Doppler ultrasound are that it is non-invasive, relatively cheap, can be performed with portable machines, allows monitoring for prolonged periods, and has a high temporal resolution making it ideal for studying dynamic cerebrovascular responses. In addition it has recently been demonstrated that it can be used to detect circulating cerebral emboli; these cannot be detected by any other currently available imaging modality.