Transcranial doppler educational software

When no intracranial signal is found but brain death criteria are met, we perform a brain CT perfusion or angiography to detect CCA. We assess cerebral autoregulation CA at the bedside as altered CA is related with a poor outcome in many diseases and may increase the risk of cerebral damage [ 9 ]. Clinicians have to consider that the monitoring of dynamic autoregulation, using the mean flow index Mx , which is calculated as the correlation coefficient indices between FV and CPP during spontaneous fluctuations in blood pressure, would be more accurate to assess CA [ 11 ].

Detection of cerebral vasospasm following aneurysmal subarachnoid hemorrhage SAH is crucial as this is one of the main determinants of delayed cerebral ischemia and poor neurological outcome in this setting [ 12 ]. Although angiography remains the gold standard, we use TCD daily to assess vasospasm, to guide additional investigations, and to monitor the clinical treatment.

Indeed, we evaluate the constriction of the cerebral vessels that is associated with a progressive increase of mean FV [ 13 ]. In the presence of clinical suspicious of vasospasm i. For other intracranial vessels, in the absence of validated mFV cutoffs, we combine clinical examination, repeated TCD showing a progressive increase in FV, and CT perfusion to detect vasospasm.

We often use TCD to monitor brain hemodynamics in critically ill patients. Future TCD development, such as the assessment of the compliance of arterial and cerebrospinal fluid compartment as well as critical capillary closing pressure, will further expand its use in this setting [ 1 ]. Transcranial Doppler: a stethoscope for the brain-neurocritical care use. J Neurosci Res. Brain ultrasonography: methodology, basic and advanced principles and clinical applications.

A narrative review. Intensive Care Med. Article Google Scholar. Transcranial Doppler ultrasound goal-directed therapy for the early management of severe traumatic brain injury. Ultrasound non-invasive measurement of intracranial pressure in neurointensive care: a prospective observational study. PLoS Med. The accuracy of transcranial Doppler in excluding intracranial hypertension following acute brain injury: a multicenter prospective pilot study. Crit Care.

Doppler non-invasive monitoring of ICP in an animal model of acute intracranial hypertension. Neurocrit Care. Latin American consensus on the use of transcranial Doppler in the diagnosis of brain death. Rev Bras Ter Intensiva.

Time dependent validity in the diagnosis of brain death using transcranial Doppler sonography. J Neurol Neurosurg Psychiatry. Further understanding of cerebral autoregulation at the bedside: possible implications for future therapy.

Expert Rev Neurother. Panerai RB. Transcranial Doppler for evaluation of cerebral autoregulation. Clin Auton Res. Monitoring of cerebral autoregulation in head-injured patients. Try out PMC Labs and tell us what you think. Learn More. Transcranial Doppler TCD ultrasound provides rapid, noninvasive, real-time measures of cerebrovascular function. TCD can be used to measure flow velocity in the basal arteries of the brain to assess relative changes in flow, diagnose focal vascular stenosis, or to detect embolic signals within these arteries.

TCD can also be used to assess the physiologic health of a particular vascular territory by measuring blood flow responses to changes in blood pressure cerebral autoregulation , changes in end-tidal CO 2 cerebral vasoreactivity , or cognitive and motor activation neurovascular coupling or functional hyperemia.

TCD has established utility in the clinical diagnosis of a number of cerebrovascular disorders such as acute ischemic stroke, vasospasm, subarachnoid hemorrhage, sickle cell disease, as well as other conditions such as brain death. Clinical indication and research applications for this mode of imaging continue to expand.

In this review, the authors summarize the basic principles and clinical utility of TCD and provide an overview of a few TCD research applications. Transcranial Doppler TCD ultrasonography provides a relatively inexpensive, noninvasive real-time measurement of blood flow characteristics and cerebrovascular hemodynamics within the basal arteries of the brain.

The physiologic data obtained from these measurements are complementary to structural data obtained from various modes of currently available vascular imaging. TCD is the most convenient way to monitor vascular changes in response to interventions during acute cerebrovascular events at the bedside.

Given the convenience of this tool as a diagnostic modality, its clinical and research applications will continue to increase in the many disorders of the cerebral vessel. TCD ultrasonography is based on the principle of the Doppler effect. According to this principle, ultrasound waves emitted from the Doppler probe are transmitted through the skull and reflected by moving red blood cells within the intracerebral vessels.

Because blood flow within the vessel is laminar, the Doppler signal obtained actually represents a mixture of different Doppler frequency shifts forming a spectral display of the distribution of the velocities of individual red blood cells on the TCD monitor Fig. The specific parameters obtained from this spectral analysis include peak systolic velocity Vs , end diastolic velocity Vd , systolic upstroke or acceleration time, pulsatility index PI , and time-averaged mean maximum velocity V mean.

The formula that describes the relationship between flow velocity reflector speed and Doppler shift frequency is. If the angle is zero, or the emitted wave is parallel to the direction of flow, the cosine of zero is 1, and we have achieved the most accurate measure of flow velocity. The larger the angle, the larger is the cosine of the angle; hence, the greater is the error in our velocity measure.

In addition, the velocity of blood flow through a vessel is proportional to the fourth power of the vessel radius. A number of physiologic variables can impact blood flow velocity as measured by TCD. The most robust of these variables are age, gender, hematocrit, viscosity, carbon dioxide, temperature, blood pressure, and mental or motor activity.

Therefore, it is important to remember that during the course of a TCD study, any measured differences in blood flow velocity should be interpreted in the context of these variables. All studies should be conducted with the patients at rest—not speaking or moving their limbs. Blood flow velocities in the basal arteries of the brain decline an average of 0. Hematocrit and viscosity are inversely related to cerebral blood flow velocity.

Partial pressure of CO 2 has also been shown to have a major influence on cerebral blood flow velocity 10 , 16 for a detailed review of this topic, please refer to the section Cerebral Vasoreactivity. Measured blood flow velocity can also be higher with higher systemic blood pressures despite an intact autoregulatory system.

The analysis of velocity measurements are particularly challenging in these patients. The effect of temperature on cerebral blood flow velocities is not well established. Although one study showed an inverse relationship between temperature and flow velocities, 18 a more recent study of TCD flow velocities in postcardiac arrest patients treated with hypothermia does not support a relationship between temperature and flow velocities.

Two types of TCD equipment are currently available: non-duplex nonimaging and duplex imaging devices. Specific vessel identification is based on standard criteria, which includes the cranial window used, orientation of the probe, depth of sample volume, direction of blood flow, relationship to the terminal internal carotid artery, and response to various maneuvers such as the common carotid artery compression and eye opening and closing.

The imaging B-mode transcranial color-coded duplex TCCD combines pulsed wave Doppler ultrasound with a cross-sectional view of the area of insonation, which allows identification of the arteries in relation to various anatomic locations. The color-coded Doppler also depicts the direction of the flow in relation to the probe transducer while recording blood flow velocities.

However, in TCCD, the angle of insonation can be measured and used to correct the flow velocity measurement. It uses several overlapping sample volumes to simultaneously display flow signals. Although these imaging TCD modalities significantly increase the reliability of TCD with better insonation angle correction, 21 the clinical applications of the more recent imaging modalities are still under development and most of the currently utilized clinical applications have been best developed using the nonduplex mode of TCD.

Therefore, the focus of this review will be on the examination and clinical applications of the nonduplex TCD. The higher frequency probes used in extracranial Doppler studies are not applicable for intracranial measurements because higher frequency waves are not able to adequately penetrate through the skull.

Therefore, familiarity with the anatomic location of cerebral arteries relative to the acoustic windows and blood flow velocities for the various arteries is critical for accurate blood flow measurements through the nonduplex mode. In general, four main acoustic windows have been described: 1 the transtemporal window, 1 2 the transorbital window, 25 3 the submandibular window, and 4 the suboccipital window Fig.

Although each window has unique advantages for different arteries and indications, a complete TCD examination should include measurements from all four windows and the course of blood flow at various depths within each major branch of the circle of Willis should be assessed.

See references 10 , 26 , and 27 for detailed reviews on examination techniques and basal cerebral artery anatomy. Specific arteries of the circle of Willis are identified using the following criteria: 1 relative direction of the probe within a specific acoustic window, 2 direction of blood flow relative to the probe, 3 depth of insonation, and 4 in difficult cases when it is not possible to differentiate the anterior from the posterior circulation, the blood flow response to carotid compression or vibration may be used.

Four acoustic windows commonly used in transcranial Doppler examination: transtemporal window A , submandibular window B , transorbital window C , suboccipital window D. The transtemporal window consists of an anterior, middle, and posterior window. However, in practice, there is usually only one useful window.

Using this window, the intracranial carotid artery ICA bifurcation can be identified at depths of 55 to 65 mm with simultaneous flow toward and away from the probe as the ICA bifurcation terminates in the anterior flow away from the probe and middle flow toward the probe cerebral arteries ACA and MCA. The ICA terminus is a convenient anatomic landmark to locate the vessels of the anterior circulation. The ACA, which can be viewed at depths of 60 to 70 mm, begins coursing medially and then anteriorly after the ICA bifurcation.

The ACA flow should be away from the probe. The posterior cerebral artery PCA can also be insonated through the transtemporal window. It is important to note that in individuals where the PCA derives most of its flow from the ICA through a large posterior communicating artery Pcom , the so-called fetal PCA configuration, the P1 segment is hypoplastic and may be very difficult to identify.

The transorbital window can be used to examine the carotid siphon and the ophthalmic artery. In addition to the amount of energy, the total time of insonation also needs to be considered and kept to a minimum to avoid further soft tissue damage.

Flow direction can be used to identify the different segments of the siphon. In general, flow is toward the probe in the infraclinoid siphon, flow in the genu is bidirectional, and flow is away from the probe in the supraclinoid segment of the siphon.

The ophthalmic artery can be found at depths of 40 to 50 mm. Flow in the ophthalmic artery should be toward the probe. The suboccipital window with the neck flexed, can be used to insonate the basilar and vertebral arteries. The basilar artery is typically found at depths of 60 to 70 mm and can sometimes be followed to depths up to mm.

Although the basilar artery is found with probe directed medially, vertebral arteries are best insonated with the probe slightly shifted laterally, at a depth of 80 to mm. Flow at the top of the basilar and in the vertebral arteries is typically away from the probe.

The submandibular window is at the angle of jaw and can be used to locate the distal ICA in the neck at a depth of 40 to 60 mm. Flow at this point is usually away from the probe. A detailed review of adult and pediatric TCD applications is beyond the scope of this article; this review will mostly focus on TCD in adults. For a detailed review of pediatric TCD applications, please refer to Verlhac. Angiographic cerebral vasospasm VSP occurs in two-thirds of patients with aneurysmal SAH with half becoming symptomatic.

Proximal VSP in any intracranial artery results in segmental or diffuse elevations of the mean flow velocities without a parallel flow velocity increase in the feeding extracranial arteries such as the carotid or the vertebral arteries. Therefore, increased PI, indicating increased resistance distal to the site of insonation, is used as a surrogate measure of distal VSP.

Sporadic measurements, especially if started after the development of vasospasm, are less useful. TCD is particularly useful in acute ischemic stroke where repeated TCD studies can be used to track the course of an arterial occlusion before and after thrombolysis. Recent studies suggest that ultrasound may also have an independent effect in augmenting thrombolysis of the occluded vessel in patients presenting with acute thrombosis.

In addition, early TCD findings can be very useful for prognosis in patients presenting with acute ischemic stroke. In these patients, intracranial arterial occlusion detected by TCD is associated with poor day outcome, 48 , 49 whereas a normal TCD study is predictive of early recovery.

Knowledge of collateral flow patterns of the basal arteries of the brain has significant clinical implications in the management of patients with cerebrovascular atherothrombotic disease. A number of clinical studies have established that the degree of collateral flow is correlated with infarct volume and clinical outcome in patients with ischemic stroke. Flow direction in these vessels will depend on the direction of collateralization and will identify the donor and recipient arterial systems.

Children with sickle cell disease SCD have chronic hemolysis resulting in low hemoglobin content. Chronic anemia and hypoxia trigger angiogenesis and neovascularization. In addition, the interaction of the sickled red cells with the endothelium causes inflammation and intracranial stenosis.

The compromised vascular system predisposes these children to both ischemic and hemorrhagic infarcts. There were no strokes in the group that continued periodic transfusion. In another retrospective cohort of children, the incidence of stroke declined fold following TCD screening and prophylactic blood transfusion over an 8-year period.

Because early TCD screening coupled with prophylactic transfusion seems to reduce overt stroke in children with SCD, TCD assessment should now be a routine component of preventive care for these children. TCD screening should be avoided during acute illnesses because factors such as hypoxia, fever, hypoglycemia, and worsening anemia may impact flow velocity measures.

TCD is the only medical device that can detect circulating cerebral microemboli, both solid and gaseous, in real-time. TCD microemboli detection is based on backscatter of the ultrasound waves from the emboli resulting in high-intensity transient signals HITS or embolic signals in the Doppler spectrum as they travel through the insonated vessel Fig. Embolic signals using TCD ultrasound have been detected in patients with carotid stenosis, myocardial infarction, atrial fibrillation, and mechanical cardiac valves.

Embolic signals on transcranial Doppler recordings of the left middle cerebral artery. Arrows indicate the high-intensity transient signals HITS seen with emboli.

Although the presence of embolic signals was predictive of ischemic events during follow-up in both symptomatic and asymptomatic patients, for the asymptomatic patients embolic signals predicted a further ischemic event with an adjusted OR of 8. In this group, embolic signals in asymptomatic patients predicted short-term ipsilateral stroke and TIA risk with an OR of 4. Patients with embolic signals were randomized to combination antithrombotic therapy with clopidogrel and aspirin or to aspirin therapy alone.

TCD recording in the ipsilateral MCA on day 7 of the treatment showed that the combination therapy was more effective than aspirin alone in reducing embolic signals. Embolic signals were present in 77 of the patients screened and the hazard ratio HR for the risk of ipsilateral stroke and TIA from baseline to 2 years in patients with embolic signals compared with those without was 2.

The results of the ACES trial suggest that TCD microemboli detection may be a useful approach to not only identify patients with asymptomatic carotid stenosis who are at high risk of stroke and TIA and who may benefit from endarterectomy, but to also identify those low-risk patients in whom surgical intervention may not be beneficial. A decrease in cerebral perfusion pressure associated with increases in ICP and PI result in compression of the intracranial arteries and cessation of flow to the brain, leading to cerebral circulatory arrest CCA.

When the ICP increases to match the diastolic perfusion pressure, diastolic cerebral blood flow approaches zero. With continued rise in ICP, diastolic blood flow reappears, but it is in the opposite direction reversed flow , visualized as retrograde flow in the TCD. Systolic waveforms also become spiked. The retrograde or oscillatory diastolic flow along with systolic spikes, result in no net forward cerebral blood flow and are characteristic of CCA.

Thanks to recent development in computers, it is now possible to represent detailed hemodynamic events in real time — this was previously only possible using supercomputers or analog circuits to solve the differential equations. The Virtual Reality Model has been integrated with e-book text to give a comprehensive course in Cerebral Hemodynamics and Transcranial Doppler.

Even 3-D models of the anatomy of the cerebral arteries are included for training of hands-on ultrasound probe handling. Cerebrovascular Diseases can be realistically explored and studied in the the Transcranial Doppler Simulator. The study material includes a variety of of cerebrovascular pathology :.