초록 열기/닫기 버튼
Transcranial Doppler ultrasonography (TCD) is a non-invasive and relatively cheap method of evaluating cerebral hemodynamics, allowing repeated measurements and continuous monitoring. Use of low frequency (2 MHz) ultrasound to penetrate bony window, and application of pulsed-wave Doppler mode allowing determination of the depth of the insonated vessels are two technical points. TCD measures velocity rather than flow, and therefore provides an estimation of cerebral blood flow only if vessel diameter remains unchanged. Mean flow velocity (MFV) and pulsatility index (PI) are the most commonly used parameters, which are influenced by various physiological variables and pathologic conditions. In clinical practice, detection of stenosis of the basal intracerebral arteries (>50-60%) is widely used, which is specific though not sensitive. Identification of occlusion or recanalization of vessels in acute stroke may provide useful information for thrombolytic therapy and prognosis. Monitoring of microembolic signal (MES) is a challenging field to detect the high-risk patients in asymptomatic carotid stenosis, and to evaluate the efficacy of anti-thrombotic therapy. CO2 or acetazolamide reactivity test is a useful method to detect significantly impaired hemodynamic reserve in patients with carotid occlusion, in which surgical revascularization may be beneficial. Newly developed echo-contrast agents and power Doppler instrument, which are expected to overcome the current technical limitation, and further progress of the transcranial color-duplex sonography also light up the future of neurosonology
