Transcranial doppler: Technique and common findings (Part 1)

Transcranial Doppler (TCD) can be aptly called as the doctor’s stethoscope of the brain. Since its introduction in 1982, by Rune Aaslid, TCD has evolved as a diagnostic, monitoring, and therapeutic tool. During evaluation of patients with acute ischemic stroke, TCD combined with cervical duplex ultrasonography provides physiological information on the cerebral hemodynamics, which is often complementary to structural imaging. Currently, TCD is the only diagnostic tool that can provide real time information about cerebral hemodynamics and can detect embolization to the cerebral vessels. TCD is a noninvasive, cost-effective, and bedside tool for obtaining information regarding the collateral flow across various branches of the circle of Willis in patients with cerebrovascular disorders. Advanced applications of TCD help in the detection of right-to-left shunts, vasomotor reactivity, diagnosis, and monitoring of vasospasm in subarachnoid hemorrhage and as a supplementary test for confirmation of brain death. This article describes the basic ultrasound physics pertaining to TCD insonation methods, for detecting the flow in intracranial vessels in addition to the normal and abnormal spectral flow patterns.     

Role of transcranial Doppler ultrasonography in evaluation of patients with cerebrovascular disease

Transcranial Doppler ultrasonography (TCD) is the only noninvasive examination method that enables the reliable evaluation of blood flow from the basal intracerebral vessels, adding physiologic information to the anatomic images. TCD is relatively inexpensive, can be performed at bedside, and allows monitoring in acute emergency settings and for prolonged periods with a high temporal resolution, making it ideal for studying dynamic cerebrovascular responses. In acute stroke, TCD is capable of providing rapid information about the hemodynamic status of the cerebral circulation and monitoring recanalization in real-time, with a potential for enhancing tissue plasminogen activator-induced thrombolysis. Extended applications such as emboli monitoring, right-to-left shunt detection, and vasomotor reactivity make TCD an important and valuable tool for evaluating stroke mechanisms, planning and monitoring treatment, and determining prognosis.     

Role of diagnostic ultrasound in patient selection for stroke intervention

Ultrasonography provides a unique diagnostic perspective in cerebrovascular disorders, with extremely high temporal resolution and excellent spatial display of extracranial as well as intracranial arteries. Unlike other imaging modalities, cerebrovascular ultrasound provides real-time information about the blood flow in addition to the hemodynamic changes as a result of various physiological as well as pathological states. The information obtained from cerebrovascular ultrasound has diagnostic, therapeutic as well as prognostic value in various disease states. Transcranial Doppler ultrasonography (TCD) is the only non-invasive examination that provides a reliable evaluation of intracranial blood flow patterns in real-time, adding physiological information to the anatomical information obtained from other neuroimaging modalities. Cerebrovascular ultrasonography is relatively cheap, can be performed bedside, and allows monitoring both in acute emergency settings as well as for prolonged periods with a high temporal resolution. Extended applications of TCD provide important information about the pathophysiology of cerebrovascular ischemia. Advanced applications of cerebrovascular ultrasonography have become an integral part of the armamentarium of stroke neurologists for evaluating stroke mechanisms, plan and monitor treatment and determine prognosis. It has been suggested as an essential component of a comprehensive stroke center. We have reviewed various recent patents in addition to the established applications of cerebrovascular ultrasonography in patient selection for various stroke interventions.     

经颅多普勒超声在重型颅脑创伤救治中的临床应用

重型颅脑创伤（sTBI）的临床监测手段多以体格检查、影像学检查为主,而这些手段无法迅速有效地诊断、监测sTBI病理生理过程。经颅多普勒超声（TCD）可以无创、实时地测量大脑大动脉的血流状态,获得脑血流动力学信息,通过分析脑血流速度及方向、血管自身调节功能、远端血管阻力变化来监测脑血管狭窄、痉挛程度并评估颅内压、识别脑死亡。本文围绕TCD在sTBI救治中的临床应用综述如下。     

Transcranial Doppler and Transcranial Color Duplex in Defining Collateral Cerebral Blood Flow

In an acute stroke setting, transcranial Doppler (TCD) and transcranial color‐coded duplex (TCCD) have an important diagnostic utility in the monitoring of an arterial occlusion and microemboli detection. In addition, TCD has proven to be a very useful tool in the detection and progression of cerebral vasospasm in patients with subarachnoid hemorrhage. TCD/TCCD may have an important role in defining collateral blood flow (CF) in stroke patients. It is a noninvasive technique and can be utilized repeatedly allowing for changes in the blood flow dynamics as treatment is delivered. In this review, we outlined the evolving role of TCD/TCCD in defining CF in patients with an acute ischemic stroke, predicting clinical outcome and monitoring the treatment's efficacy of the CF augmentation.     

Transcranial Doppler ultrasonography in the neurologic intensive care unit

Transcranial doppler ultrasonography (TCD) is a noninvasive monitoring tool which allows imaging of blood flow velocities in intracranial blood vessels. It is safe, portable, easy to perform and provides accurate information regarding underlying physiology which may help to guide therapy in critically ill neurologic patients. It has significantly contributed to the management of vasospasm related to subarachnoid hemorrhage in the neurologic intensive care unit. TCD is also helpful in the early diagnosis of a variety of complications that can occur in patients with head injury such as vasospasm, elevated intracranial pressure and disordered cerebral autoregulation. Careful performance of the test and experienced interpretation can identify TCD waveforms indicative of cerebral circulatory arrest, an ancillary finding used for the diagnosis of brain death. TCD is likely to play a larger role in evaluation of the patient in the future because of its safety, portability and ability to define moment-to-moment changes in cerebral blood flow velocities and cerebral blood flow.     

Non‐Invasive Intracranial Pressure Monitoring with Transcranial Doppler in a Patient with Progressive Cerebral Venous Sinus Thrombosis

In many intracranial disease states, monitoring of intracranial pressure (ICP) is essential to evaluate response to the therapeutic measures as well as estimation of prognosis. Although, direct estimation of ICP is reliable, it is invasive and not possible in all patients. Transcranial Doppler (TCD) ultrasonography is a bedside and noninvasive technique that provides reliable and real‐time information about cerebral hemodynamics. We present a case of extensive and progressive cerebral venous sinus thrombosis in which TCD served as an excellent tool for monitoring ICP and the serial observations correlated closely with clinical status and ophthalmological findings.     

Practice Standards for Transcranial Doppler (TCD) Ultrasound. Part II. Clinical Indications and Expected Outcomes

ABSTRACT

INTRODUCTION

Transcranial Doppler (TCD) is a physiological ultrasound test with established safety and efficacy. Although imaging devices may be used to depict intracranial flow superimposed on structural visualization, the end‐result provided by imaging duplex or nonimaging TCD is sampling physiological flow variables through the spectral waveform assessment.

SUMMARY OF RESULTS

Clinical indications considered by this multidisciplinary panel of experts as established are: sickle cell disease, cerebral ischemia, detection of right‐to‐left shunts (RLS), subarachnoid hemorrhage, brain death, and periprocedural or surgical monitoring. The following TCD‐procedures are performed in routine in‐ and outpatient clinical practice: complete or partial TCD‐examination to detect normal, stenosed, or occluded intracranial vessels, collaterals to locate an arterial obstruction and refine carotid‐duplex or noninvasive angiographic findings; vasomotor reactivity testing to identify high‐risk patients for first‐ever or recurrent stroke; emboli detection to detect, localize, and quantify cerebral embolization in real time; RLS‐detection in patients with suspected paradoxical embolism or those considered for shunt closure; monitoring of thrombolysis to facilitate recanalization and detect reocclusion; monitoring of endovascular stenting, carotid endarterectomy, and cardiac surgery to detect perioperative embolism, thrombosis, hypo‐ and hyperperfusion.

CONCLUSION

By defining the scope of practice, these standards will assist referring and reporting physicians and third parties involved in the process of requesting, evaluating, and acting upon TCD results.     

The evolving role of transcranial doppler in stroke prevention and treatment.

Without focusing on established indications for transcranial Doppler (TCD) such as monitoring vasospasm after subarachnoid hemorrhage and detecting intracranial stenosis (sickle cell disease, stroke, etc.), we describe the role of TCD in carotid endarterectomy (CEA) and angioplasty, acute ischemic stroke, as well as competence and the practice of TCD. In addition to duplex ultrasound and angiography TCD can be used to select patients for CEA because it detects hemodynamically significant extracranial stenosis and tandem intracranial stenoses, and identifies asymptomatic patients at potentially high risk of stroke because of exhausted vasomotor reactivity or brain microembolization. TCD identifies in real time brain hypoperfusion, embolism, and hyperperfusion and thus may be helpful in reducing cerebrovascular complications of CEA/angioplasty. In acute ischemic stroke, TCD can reliably identify the patency of middle cerebral and basilar arteries, high resistance flow patterns due to increased intracranial pressure, and progression to cerebral circulatory arrest. TCD also can monitor spontaneous or induced arterial recanalization. Limitations include operator and interpreter dependency, absent temporal "windows" leading to unsuccessful insonation in 10% to 15% of patients older than 60 years, as well as difficulties with probe positioning and fixation for monitoring. However, the use of ultrasound contrast agents and improved probe fixation devices help avoid these factors. The key to the successful practice of TCD is training of technical personnel and education of the interpreting and referring physicians as to when to use TCD and what to expect from it. The advantages of TCD should be given particular consideration: portability, repeatability, long-term monitoring, emboli detection, and inexpensiveness. TCD machines and transducers need to be tuned to the target disorders; that is, larger sample volume, higher power, and so forth, and TCD technology should be implemented in phases I to II as well as in phase III trials of preventive interventions and stroke therapies.     

Transcranial Doppler

TCD recording of flow velocities in intracranial vessels was first described by Aaslid in 1982. The utility of this instrument becomes more apparent as it is used in different clinical settings and compared with angiographic findings (Figures 1 and 2). Its importance in early detection of vasospasm in subarachnoid hemorrhage is now clearly known; increased flow velocity can be documented prior to neurologic deterioration and thus allow early institution of therapy. In patients with stroke or transient ischemic attack of unclear etiology, especially in blacks, Orientals, or females, who have a higher incidence of intracranial arterial disease, TCD can be a very important noninvasive means for detecting stenosis of intracranial vessels. Its value for assessing collateral circulation, intraoperative monitoring, and measuring CBF is quite promising. Hopefully, through further work with TCD, we will be able to clarify the spectrum of its usages as well as its limitations, though the preliminary data indicate that it should be an important addition to present noninvasive evaluations.     

Diagnostic impact of early transcranial Doppler ultrasonography on the TOAST classification subtype in acute cerebral ischemia

OBJECTIVE: The impact of early transcranial Doppler ultrasonography (TCD) upon stroke subtype diagnosis is unknown and may affect therapeutic strategies. In this study, the diagnostic usefulness of TCD in stroke subtype diagnosis according to the criteria of the Trial of ORG 10172 in Acute Stroke Treatment (TOAST) study was investigated in patients with acute cerebral ischemia. METHODS: TCD examination within 24 h of symptom onset was performed in 50 consecutive patients with acute cerebral ischemia. Of these 54% were female. Sixty percent of patients were black, 36% white, and 4% Asian. Initial TOAST stroke subtype diagnosis (ITSSD) was based upon clinical presentation and initial brain imaging studies. Modified TOAST stroke subtype diagnosis was determined subsequently after additional review of the TCD examination. Final TOAST stroke subtype diagnosis was determined at hospital discharge, incorporating all diagnostic studies. Using final TOAST stroke subtype diagnosis as the 'gold standard' ITSSD and modified TOAST stroke subtype diagnosis were compared in order to determine additional benefit from the information obtained by TCD. Data were collected retrospectively by a single investigator. RESULTS: ITSSD classified 23 of 50 (46%) patients correctly. After TCD, 30 of 50 (60%) patients were classified correctly, for an absolute benefit of 14% and a relative benefit of 30% (p = 0.018). Most benefit from TCD was observed in the TOAST stroke subtype category large-artery atherosclerosis, in particular in patients with intracranial vascular disease. In this category, ITSSD had a sensitivity of 27% which increased to 64% after TCD (p = 0.002). CONCLUSION: TCD within 24 h of symptom onset improves the accuracy of early stroke subtype diagnosis in patients with acute cerebral ischemia due to large-artery atherosclerosis. This may have clinical implications for early therapeutic interventions.     

Sonographic monitoring of mass effect in stroke patients treated with hypothermia. Correlation with intracranial pressure and matrix metalloproteinase 2 and 9 expression

Severe stroke leads to subsequent cerebral oedema. Patients with severe stroke develop midline shift (MLS) which can be measured by transcranial duplex sonography (TCD). We measured MLS with TCD in 30 patients with large infarction in the territory of the middle cerebral artery (MCA). All of the examined patients had intracranial pressure (ICP) measure devices and the ICP at the time of the TCD was recorded. MLS was also determined on CT scan on day 4. Ten of the 30 patients were treated with hypothermia. We also determined matrix metalloproteinase 2 (MMP2) and matrix metalloproteinase 9 (MMP9) in serum by zymography. MLS measured by TCD correlated significantly with MLS on CT. In addition there was a strong correlation between the ICP measured at the time of TCD and MLS. In patients treated with hypothermia MLS was less pronounced. MMP9 and MMP2 showed a characteristic time course and had strong associations with MLS. We confirm earlier reports that TCD is a reliable noninvasive method for serially monitoring patients with intracranial lesions. Hypothermia reduces MMP9 activity as well as MLS. TCD may reduce the need for repetitive CT scans in neurological critically ill patients.     

Association of intraoperative transcranial doppler monitoring variables with stroke from carotid endarterectomy

BACKGROUND AND PURPOSE: The outcomes of carotid endarterectomy (CEA) are, in addition to patient baseline characteristics, highly dependent on the safety of the surgical procedure. During the successive stages of the operation, transcranial Doppler (TCD) monitoring of the middle cerebral artery (MCA) was used to assess the association of cerebral microembolism and hemodynamic changes with stroke and stroke-related death. METHODS: By use of data pooled from 2 hospitals in the United States and the Netherlands, including 1058 patients who underwent CEA, the association of various TCD emboli and velocity variables with operative stroke and stroke-related death was evaluated by univariable and multivariable logistic regression analyses in combination with receiver operating characteristic (ROC) curve analyses. The impact of basic patient characteristics, such as age, sex, preoperative cerebral symptoms, and ipsilateral and contralateral internal carotid artery stenosis, on the prediction of operative stroke was also evaluated. RESULTS: We observed 31 patients with ischemic and 8 patients with hemorrhagic operative strokes. Four of these patients died. Emboli during dissection (odds ratio [OR] 1.5, 95% CI 0.8 to 2.9) and wound closure (OR 2.3, 95% CI 1.2 to 4.4) as well as > or =90% decrease of MCA peak systolic velocity at cross-clamping (OR 3.3, 95% CI 1.3 to 8.5) and > or =100% increase of the pulsatility index of the Doppler signal at clamp release (OR 7.1, 95% CI 1.4 to 35.7) were independently associated with stroke. The ROC area of this model was 0.69. Of the patient characteristics, only preoperative cerebral ischemia (OR 1.9, 95% CI 1.0 to 3.7) and > or =70% ipsilateral internal carotid artery stenosis (OR 0.5, 95% CI 0.2 to 0.9) were associated with stroke. Adding these patient characteristics to the model, the area under the ROC curve increased to 0.73. CONCLUSIONS: In CEA, TCD-detected microemboli during dissection and wound closure, > or =90% MCA velocity decrease at cross-clamping, and > or =100% pulsatility index increase at clamp release are associated with operative stroke. In combination with the presence of preoperative cerebral symptoms and > or =70% ipsilateral internal carotid artery stenosis, these 4 TCD monitoring variables reasonably discriminate between patients with and without operative stroke. This supports the use of TCD as a potential intraoperative monitoring modality to alter the surgical technique by enhancing a decrease of the risk of stroke during or immediately after the operation.     

经颅多普勒超声在脑侧支循环评估中的临床应用

脑侧支循环的建立对于缺血性卒中的预后至关重要,便捷有效的脑侧支循环评估方法对 于临床预测卒中患者预后、血管再通治疗效益与风险评价尤为重要。TCD因其可实时检测脑血流动力 学指标、无创伤、可重复、操作便捷、廉价等优点在脑侧支循环评估中发挥着不可替代的作用。本文 检索文献就TCD对脑一、二级侧支循环和脑血管反应性的检测方法、意义及临床应用进展进行综述, 以期为临床诊疗提供帮助。     

TCD动态监测静脉窦血栓形成五例

目的评价静脉窦血栓形成患者经颅多普勒超声(TCD)检测静脉侧枝的开放和再通情况以及颅内压变化。方法用TCD 2MHz探头检测5例静脉窦血栓形成患者的颅内静脉的血流速度以及动脉频谱形态的变化。结果 5例静脉窦血栓形成患者的颅内静脉(大脑中深静脉、基底静脉)的血流速度均明显增高(139cm/s,118 cm/s,99 cm/s,103 cm/s,58cm/s),动脉频谱呈高阻力,经过治疗,随着病情的好转,颅内静脉血流速度下降,颅内动脉频谱由高阻力型恢复正常。结论 TCD能可靠无创、准确地检测颅内静脉,在病程中通过多次的TCD检查,可以评价静脉窦血栓形成静脉侧枝的开放和再通情况以及颅内压变化。     

Emergency EEG and continuous EEG monitoring in acute ischemic stroke.

There is physiologic coupling of EEG morphology, frequencies, and amplitudes with cerebral blood flow. Intraoperative continuous electroencephalographic monitoring (CEEG) is an established modality that has been used for 30 years to detect cerebral ischemia during carotid surgery. These facts have generated interest in applying EEG/CEEG in the intensive care unit to monitor cerebral ischemia. However, its use in acute ischemic stroke (AIS) has been limited, and its value has been questioned in comparison with modern MRI imaging techniques and the clinical neurologic examination. This review presents evidence that EEG/CEEG adds value to early diagnosis, outcome prediction, patient selection for treatment, clinical management, and seizure detection in AIS. Research studies correlating EEG/CEEG and advanced imaging techniques in AIS are encouraged. Improvements in real-time ischemia detection systems are needed for EEG/CEEG to have wider application in AIS.     

经颅多普勒超声监测下颈动脉内膜切除术后脑血流过度灌注临床研究简

目的探讨颈动脉内膜切除术后脑血流过度灌注临床特点和经颅多普勒超声（TCD）监测下治疗脑血流过度灌注之疗效。方法回顾分析2013年1—8月实施颈动脉内膜切除术且行TCD监测的60例（63例次）患者的临床资料,根据围手术期TCD监测结果判断患者是否存在脑血流过度灌注或脑过度灌注综合征。结果术后7d三维CTA检查显示,60例（63例次）患者颈动脉狭窄完全解除,术后30d内不良事件发生率分别为轻度缺血性卒中（1例次占1．59％）、心肌梗死（1例次占1．59％）、声音嘶哑（1例次占1．59％）,无脑出血和死亡病例。术后脑血流过度灌注4例次（6．35％）,持续1～3d,其中1例次（1．59％）为脑过度灌注综合征,表现为精神亢奋,幻觉和睡眠障碍。术后视力明显改善3例次占4．76％,其中1例次发生脑血流过度灌注。结论颈动脉内膜切除术围手术期TCD监测可以早期发现术中和术后脑血流过度灌注,及时根据TCD监测结果控制血压异常变化,是减少术后脑出血并发症之关键。     

The potential and limitations of transcranial Doppler in clinical practice

The aim of this review is to bring the clinical relevance of transcranial Doppler (TCD) to light with all of its possibilities and limitations. Indeed, TCD, a non-invasive ultrasound technique, allows instantaneous evaluation of the cerebral blood flow, adding physiological information to the anatomical images. Although TCD is frequently used in some places, in other regions TCD remains relatively unknown. However, TCD can help the neurologist not only in the management of cerebrovascular disease, but also in a wide variety of central nervous system disorders. TCD monitoring with multichannel and multigate probes can assess vascular reactivity by following various parameters, such as CO2 or arterial blood pressure. Despite the need for more work, emboli detection seems to offer great potential in the future diagnosis, treatment, and prevention of stroke.     

Transcranial Doppler Markers of Diffusion-Perfusion Mismatch

BACKGROUND AND PURPOSE: During the evaluation of acute ischemic stroke with diffusion- and perfusion-weighted magnetic resonance imaging (DWI and PWI, respectively), the presence of salvageable brain tissue is suggested by the occurrence of a perfusion-diffusion "mismatch." DWI and PWI, however, are not universally available and have inherent inconveniences, which justify a search for practical diagnostic alternatives. The purpose of this study is to investigate whether there are transcranial Doppler (TCD) markers of mismatch. METHODS: Retrospective analysis of 22 patients with acute ischemic stroke affecting the middle cerebral artery (MCA) territory, who had a TCD performed within 24 hours of magnetic resonance imaging (MRI) with DWI and PWI. RESULTS: MRI and TCD were performed on average 10.8 +/- 9.2 hours apart. Time from symptom onset to MRI and TCD completion were 1.6 +/- 1.6 and 2 +/- 1.9 days, respectively. MCA and intracranial internal carotid artery (ICA) cerebral blood flow velocity (CBFV) asymmetry, together with a large ICA-to-MCA gradient, were associated with the presence of mismatch. The combined use of 2 TCD parameters (MCA CBFV asymmetry of > or = 30% and ICA-to-MCA gradient > or = 20 cm/sec) had a sensitivity of 75%, specificity of 80%, positive predictive value of 82%, and negative predictive value of 73% at detecting mismatch cases. CONCLUSIONS: Diffusion-perfusion mismatch appears to be associated with interhemispheric asymmetry between MCA and ICA CBFVs, and a large CBFV gradient between the ICA and MCA on the affected side. Prospective studies are required to verify these observations and to determine whether TCD can be used to follow patients with mismatch.     

Cerebral microembolus detection in an unselected acute ischemic stroke population

OBJECTIVE: The aims of this study were firstly to determine prevalence, frequency, and clinical significance of cerebral microemboli in an unselected acute ischemic stroke population and secondly to examine how this information may improve ischemic stroke subtype classification. METHODS: We intended to perform transcranial Doppler (TCD) microembolus monitorings of the middle cerebral artery (MCA) in the symptomatic hemisphere for 45 min in 120 consecutive patients with internal carotid artery territory ischemia. The first examination was performed within 72 h from start of symptoms and the second 5 +/- 1 days later. Platelet and coagulation system activation were measured following TCD monitoring in 38 patients. The strokes were subtyped using the TOAST classification criteria, and the patients' clinical status was assessed at discharge using the Scandinavian Stroke Scale and the Barthel Index. RESULTS: Microembolus monitoring was technically possible in 83 (69.2%) of the 120 patients. Thirty-two (26.6%) patients had an inadequate temporal bone acoustic window or were too restless to allow long-time monitoring. In 5 (4.2%) patients the relevant MCA was occluded. Twenty-two (26.5%) of the 83 patients had microemboli despite the fact that over 90% were receiving an antiplatelet or an anticoagulant treatment. The mean frequency of microemboli was 6.7 +/- 13.6 per 45 min. Microemboli were more prevalent in assumed cardioembolic stroke than in other subtypes of ischemic stroke (p = 0.047). We found no association between the presence of cerebral microemboli and the clinical outcome or the parameters for platelet or coagulation system activation. The presence of microemboli was not associated with in-hospital deaths (p = 0.17), whereas MCA occlusion was (p = 0.01). CONCLUSIONS: Cerebral microemboli are frequent in unselected acute ischemic stroke patients despite antiplatelet or anticoagulant treatment. TCD detection of microemboli provides valuable pathophysiological information and may, therefore, improve current ischemic stroke subtype classification.