Transcranial Doppler Ultrasound: From Theory to Practice

Abstract

This comprehensive review by Phan Xuan Uy Hung and Hoang Tien Trong Nghia presents transcranial Doppler (TCD) ultrasound from theoretical principles to clinical practice. TCD is a non-invasive diagnostic tool that exploits the Doppler effect—the frequency shift of ultrasound waves reflected off moving red blood cells—to assess cerebral blood flow velocity, direction, and resistance using low-frequency (1-2 MHz) probes capable of penetrating the skull through acoustic windows (temporal, orbital, submandibular, and occipital/foraminal). The technique offers flexibility, low cost, and repeatability but is operator-dependent and limited by inadequate temporal bone windows in 10% of Europeans and 20-30% of Asians. The article details cerebral vascular anatomy (internal carotid and vertebrobasilar systems, Circle of Willis) and systematic scanning protocols for identifying the MCA, ACA, PCA, ophthalmic artery, carotid siphon, vertebral, and basilar arteries based on characteristic depth, direction, and velocity signatures. Clinical applications include: diagnosing intracranial stenosis using established mean flow velocity (MFV) cutoffs (SONIA and Zhao criteria), monitoring clot dissolution during intravenous thrombolysis via the TIBI grading scale, assessing vasospasm severity in subarachnoid hemorrhage using the Lindegaard and Sviri ratios, detecting right-to-left shunts (patent foramen ovale) through microembolic signal counting during bubble studies, screening for stroke prevention in sickle cell disease, and supporting brain death diagnosis. The article also outlines standardized reporting requirements for TCD studies per international consensus guidelines.