Transcranial Doppler: Techniques and advanced applications: Part 2

Abstract

Transcranial Doppler (TCD) is the only diagnostic tool that can provide continuous information about cerebral hemodynamics in real time and over extended periods. In the previous paper (Part 1), we have already presented the basic ultrasound physics pertaining to TCD, insonation methods, and various flow patterns. This article describes various advanced applications of TCD such as detection of right-to-left shunt, emboli monitoring, vasomotor reactivity (VMR), monitoring of vasospasm in subarachnoid hemorrhage (SAH), monitoring of intracranial pressure, its role in stoke prevention in sickle cell disease, and as a supplementary test for confirmation of brain death.

Keywords: Cerebral circulatory arrest; emboli; intracranial pressure (ICP); ischemic stroke; sickle-cell disease; transcranial Doppler (TCD); vasomotor reactivity (VMR); vasospasm.

Figure 1

Neuroimaging findings in a patient with severe and symptomatic carotid artery stenosis. Computerized tomographic angiography of the neck shows a focal stenosis of proximal internal carotid artery (a). The plaque characteristics and flow through the residual lumen are shown on the cervical duplex ultrasonography (b). Continuous monitoring of the ipsilateral middle cerebral artery showed multiple microembolic signals (c)

Figure 2

Assessment of cerebral vasomotor reactivity in a patient with large artery stenosis. Computerized tomographic angiography of the brain (a) Shows a severe stenosis of the right middle cerebral artery (MCA). Panel B shows the flow response in both MCAs. A normal flow acceleration during 30 s of voluntary breath-holding is noted in the left MCA. However, the right MCA shows a paradoxical reduction in the flow velocities, suggestive of an exhausted vasodilatory reserve with intracranial steal phenomenon (the reversed Robin Hood syndrome)

Figure 3

TCD findings from a 6-year-old male who underwent abdominal surgery for perforated bowel, which was complicated by recurrent episodes of ventricular fibrillation and cardiac arrest, requiring cardiopulmonary resuscitation. This TCD was performed on day 4 due to absent pupilary reflex and poor gag reflex. Alternating flow spectra were obtained from the right middle cerebral artery (MCA) and basilar artery while left MCA demonstrated only systolic spikes, suggestive of cerebral circulatory arrest

Figure 4

Serial transcranial Doppler (TCD) spectra and intracranial pressure (ICP) monitoring in a patient with encephalitis. TCD performed on day 2 shows a high resistance Doppler spectra [note the pulsatility index (PI) as 1.46]. Clinical improvement in this patient was associated with reduction of ICP (16 cm of water) and normalization of TCD-derived PI to 1.12