Using a technique termed “range gating,” modern equipment is able to selectively record signals from specific depths, allowing velocity to be recorded at distinct points along a vessel. 49 The depth of the insonated vessel can be estimated using pulsed-wave Doppler, in which the transceiver emits distinct acoustic pulses and measures the time required for their return. Inaccuracies can be introduced with this correction if the angle is incorrectly estimated, with error increasing as the angle approaches 90°. Importantly, only the component of velocity parallel to the ultrasound beam can be measured directly any angle between the direction of movement and the beam must be mathematically accounted for. 49 This difference is proportional to the velocity of the moving object if an object is stationary with respect to the transceiver, there is no Doppler shift. Familiarity with this diagnostic tool is crucial for the modern neurological surgeon.ĭoppler ultrasound detects motion using the difference in frequency between emitted ultrasonic waves and the returning echoes. As the clinical applications of TCD ultrasonography have expanded over time, so has their importance in the management of neurosurgical patients. Finally, assessment of cerebral autoregulation can be performed using TCD ultrasonography, providing data important to the management of patients with severe traumatic brain injury. TCD ultrasonography can identify patients with exhausted cerebrovascular reserve, and after extracranial-intracranial bypass procedures it can be used to assess adequacy of flow through the graft. Monitoring for microembolic signals enables stratification of stroke risk due to carotid stenosis and can also be used to clarify stroke etiology. TCD ultrasonography is also useful in the evaluation and management of occlusive cerebrovascular disease. In this setting, elevated blood flow velocities serve as a proxy for vasospasm and can herald the onset of ischemia.

One of the most common uses of TCD ultrasonography is monitoring for vasospasm following subarachnoid hemorrhage. In this review, the authors outline the technology underlying TCD ultrasonography and describe its uses in patients with neurosurgical diseases.

Transcranial Doppler (TCD) ultrasonography is an inexpensive, noninvasive means of measuring blood flow within the arteries of the brain.

Transcranial doppler interpretation