Figure 2 Windows of insonationĬerebral hemodynamics play a role in TCD performance and interpretation. Most of the arteries of the Circle of Willis are insonated via the transtemporal window, but the basilar and vertebral arteries are only accessible via the transforaminal window and the carotid siphon as well as the ophthalmic artery can only be insonated via the transorbital window. The transtemporal, transforaminal, submandibular and transorbital windows are shown below (see Figure 2). TCD has to be performed through certain “windows” because the skull attenuates the ultrasound. Figure 1 Schematic of the Doppler principle as applied insonating Velocity can also be calculated from these shifts with an assumed angle of insonance of 0o (e.g., parallel with flow). ![]() The TCD instrument is able to measure flow direction via Doppler shifts. This procedure is predicated on a few simple premises, including the Doppler Effect, windows of insonation, expected cerebrovascular anatomy, cerebral hemodynamics, and the type of data TCD provides. Absent/suboptimal windows for insonation in substantial minority of patients (~10%). ![]() TCD is a non-invasive means of measuring blood velocity and direction in large arteries of the brain OVERVIEW OF TCD ULTRASONOGRAPHY GENERAL PRINCIPLES OF TCD intraoperative monitoring of cardiac and endovascular procedures for cerebral risk from emboli.test for vasomotor instability in migraine and concussion patients.monitor response to tPA with acute stroke and inform prognosis.test for “downstream exhaustion” of cerebrovascular autoregulation.screen for vertebrobasilar insufficiency.can also identify microemboli associated with cardiac or vascular hardware, atrial fibrillation, and asymptomatic carotid artery disease that can inform management. ![]()
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