engleski

The role of transcranial doppler sonography in cerebrovascular disorders

Transcranial Doppler (TCD) is a non-invasive, fast and reliable diagnostic tool for the evaluation of cerebral hernodynamics, providing numerous informations on cerebrovascular state of the patient. The major advantages of TCD application is in revealing patients with acute vascular pathology ; classification of stroke, redistribution of intracranial hemodynamics due to extra- and intracranial occlusive disease, intracranial blood vessel stenosis, hemodynamics evaluation of tandem lesions, arteriovenous malformations, angiomas, brain death, monitoring of vasospasm, brain oedema, monitoring of different therapies (thrombolytic, antiedema and in reduction of vasospasms) and during intraoperalive monitoring- Recent TCD modalities enable detection of cerebral microembolic signals, estimation of cerebral vasoreactivity, and cerebral autoregulation by analysing cerebral microcirculatory response after stress tests such as C02 or acetazolamide reactivity, or functional tests by cognitive tasks. Transcranial Color Coded Duplex Ultrasound (TCCS) is a new method that combines the visualisation of the color coded Doppler signal to map the basal cerebral vessels, and to obtain the Doppler hemodynamic spectra within the sample volume gate for diagnostic interpretation, within the already visualised vessel. This technique enables exact localisation of the stenotic process, visualisation of the arteriovenous malformations and angiomas. It allows application of Power imaging (PDI), which is based on power Doppler processing whereby the amplitude or intensity of moving targets is displayed. It is not subject to angle dependence or alaising. The major advantages are the possibility of the imaging of tortuosity of the vessels and increased sensitivity for visualization of the vessels with lower flow velocities. With the application of contrast, blood has increased echogenicity, and the visualization of the vessels is enhanced. Thus, the fine resolution is improved, and sensitivity of color imaging by color and Doppler is increased. It displays segments of vessels undetectable on baseline precontrast scans. Cerebral venous anatomy is perfectly depicted. It can display flow where no flow was believed to be present, it can demonstrate a portion of the circle of Willis not well seen on unenhanced studies and thus increasing clinical reliability. It allows the entire circle of Willis to be imaged by the unitemporal approach. It allows exact vessel localisation in detection of AVM and demonstrates the contribution of vessels and lesion size. All this avoids the need for the potentially dangerous carotid compression tests that were previously necessary to confirm vessel identity. TCD and its modifications is an objective and easy to manage diagnostic tool for assessment of cerebral hemodynamics, very helpful in outpatient screening for cerebrovascular diseases, and irreplaceable method in intensive care units.

transcranial Doppler; cerebrovascular disease

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