Mean CBFV is calculated using a spectral envelope (also known as fast Fourier transformation) Mean CBFV 5 /3, where PSV is peak systolic CBFV and EDV is end-diastolic CBFV. The time interval between pulse emission to pulse reception determines the depth from which the Doppler shift obtained. The difference between the transmitted and received signals is known as the Doppler shift.
The ultrasonic beam that emitted from TCD probe crosses the skull at the target location and reflected from the erythrocytes which flow at different speeds in the cerebral vessels and the resultant signals are recorded. At low frequencies (2 MHz) soft tissues and bone attenuation is low compared with high frequencies, thus providing accurate recoding of cerebral blood flow velocity (CBFV). Procedure of TCD involves the placement of electrical probe of range gated ultrasonography permitting assessment of blood flow velocity in the cerebral arteries. Also, it has crucial role in carotid endarterectomy for diagnosis of hyper perfusion syndrome and prevention of its sequalae. Other clinical applications are arteriovenous malformation (AVM), diagnosis of brain death, detection of emboli and in parenchymal brain disease. This article describes the important clinical role of TCD in neuro surgical practice as in monitoring of patients with post-aneurysmal subarachnoid hemorrhage vasospasm, patient with ischemic stroke, and traumatic brain injury (TBI). Repetitive TCD monitoring may recognize recanalization during antifibrinolytic therapy for acute ischemic stroke. It provides information about of brain hemodynamics in real time. TCD represents bedside, noninvasive, cheapest, easy repetitive modality which became widely used in patients with cerebrovascular diseases. Since TCD was extensively used in outpatient, intraoperative, and critical care units. Transcranial Doppler ultrasonography (TCD) was first introduced on clinical practice in 1986. TCD is relatively cheap, can be performed bedside, and allows monitoring in acute emergency settings. The physiological information obtained from TCD is complementary to the anatomical details obtained from other neuroimaging modalities. Transcranial Doppler ultrasonography is the only diagnostic modality that provides a reliable assessment of cerebral blood flow patterns in real time. Also, it can be used for evaluation of circulatory arrest with subsequent confirmation of brain death Conclusion Transcranial Doppler ultrasonography is also the unique modality for detection of micro emboli in high-risk patients. Intracranial pressure can be monitored by pulsatility index which reflects blood flow resistance in cerebral vessels. Cerebral vessels vasospasm represented by abnormal elevation of cerebral blood flow velocity. Many diseases can lead to cerebral vessels vasospasm as in subarachnoid hemorrhage and trauma. Transcranial Doppler is a bedside procedure used to assess cerebral blood flow velocity via cerebral circulation and pulsatility index (PI). The additional information that transcranial Doppler can provide as part of a multimodal imaging protocol in many clinical settings has not been evaluated.
0 kommentar(er)
