![]() ![]() In clinical practice, the most relevant scanning plane for the study of cerebral arterial vessels is the mesencephalic plane, so our review will focus mainly on this view. The axial scan is the one most commonly used, and it allows two different types of imaging planes: The mesencephalic and diencephalic views. In general terms, transcranial US study can be performed using two main scanning planes: The axial and coronal planes at a depth that allows to display also the contralateral vessels. The transmission of an US beam through skull is influenced by structural characteristics of the diploe bone: The almost complete absence of bone spicules makes the penetration of the US similar to conventional “acoustic windows” consenting the visualization of intracranial vessels.įirst of all, the patient should be lying in supine position, with his head and shoulders on a pillow. In standard TCD examination should be recorded bilateral PW Doppler tracing lasting at least 10 cardiac cycles after a 30 s stabilized recording period. To get a better quality of the Doppler signal in spite of background noises, the TCD devices are equipped with a larger sample volume compared to other PW Doppler probe. The TCD with combined ColorFlow and power Doppler allows direct imaging of the intracranial arteries, their anatomic course, diameter, and relationships with the adjacent structures. TCD is conducted using either transcranial color-coded duplex sonography, in which it is displayed a two-dimensional color-coded image or once the desired blood vessel is insonated, blood flow velocities may be measured using Pulsed wave (PW) Doppler. The probe can then be fixed to the scalp with a headband so that the same angle of insonation for continuous flow velocity recordings is maintained throughout the examination. In clinical practice, the most frequently used transducer is a Pulsed Doppler sectorial probe with a 2.0–3.5 MHz emission frequency. ![]() In this review, we will describe physical principles underlying TCD, flow indices most frequently used in clinical practice, and critical care indications for this imaging modality. ![]() Other clinical applications of TCD include monitoring of cerebral circulation and embolization during cardiopulmonary bypass, carotid endarterectomies, and carotid artery stenting. Moreover TCD allows for intraoperative monitoring, evaluation of vasomotor function, and assessment of cerebral microembolism due to right to left cardiac shunts. TCD has important clinical application in the management of patients with sickle-cell disease, brain stem death, and raised intracranial pressure (ICP). It allows to investigate cerebral pressure autoregulation and for the clinical evaluation of cerebral autoregulatory reserve. It is also useful on both adults and children to diagnose and monitor vasospasm (VSP) after subarachnoid hemorrhage (SAH) of different etiologies (aneurysm rupture and traumatic brain injury ), and cerebral hemodynamic changes after stroke including cryptogenic stroke. TCD examinations have gained an important role in the very early phase of critical cerebral pathologies, as well as during follow-up of patients with chronic CVDs. It is inexpensive, repeatable, and allows continuous bedside monitoring of CBFV, which is particularly useful in the intensive care setting. TCD ultrasonography involves the use of a low-frequency (≤2 MHz) transducer, placed on the scalp, to insonate the basal cerebral arteries through relatively thin bone windows and to measure the cerebral blood flow velocity (CBFV) and its alteration in different cerebrovascular diseases (CVDs) and traumatic brain injuries. Transcranial Doppler (TCD) ultrasonography is a noninvasive ultrasound (US) study, which was introduced in clinical practice in 1982, since then it has been extensively applied on both outpatient and inpatient settings. ![]()
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