Intracranial Flow Patterns Research Articles

Predicting impaired cerebrovascular reactivity and risk of hyperperfusion syndrome in carotid artery stenosis using BeamSAT magnetic resonance imaging

Pencil-beam presaturation (BeamSAT) magnetic resonance imaging (MRI) produces selective magnetic resonance angiography (MRA) images of specific arteries, including the unilateral internal carotid artery (ICA-selective MRA) or vertebral artery (VA-selective MRA). We evaluate the influence of flow pattern, visualized using BeamSAT MRI, on preoperative cerebral hemodynamic status and postoperative hyperperfusion syndrome (HPS). Patients undergoing carotid artery stenting or carotid endarterectomy were categorized into two groups to evaluate flow pattern. Patients with neither crossflow on BeamSAT MRI nor mismatch in middle cerebral artery (MCA) signal intensity between ICA-selective and conventional MRA were classified into Group I, comprising 29 patients. Group II included all other patients comprising 19 patients, who were suspected of experiencing changes in intracranial flow patterns. Cerebral blood flow and cerebrovascular reactivity (CVR) were assessed using single-photon emission computed tomography, and potential HPS symptoms were retrospectively assessed by chart review. Preoperative ipsilateral CVR was significantly lower in Group II than in Group I (18.0% ± 20.0% vs. 48.3% ± 19.5%; P < 0.0001). Group II showed significantly impaired CVR (odds ratio 17.7, 95% confidence interval 1.82–171; P = 0.013) in multivariate analysis. The partial areas under the curve of the BeamSAT logistic model (0.843) were significantly larger than those of the conventional logistic model (0.626) over the range of high sensitivity (0.6–1) (P = 0.04). The incidence of postoperative HPS symptoms was significantly higher in Group II than in Group I (8/19 vs. 1/29; P = 0.001). BeamSAT MRI may be a valuable and non-invasive tool for assessing cerebral hemodynamics and predicting postoperative HPS.

Abstract WP217: 4D Flow MRI Monitoring of Pediatric Brain Arteriovenous Malformations: A Feasibility Study

Introduction: While some brain arteriovenous malformations (bAVM) demonstrate long-term stability, others demonstrate dynamic changes (new aneurysms or venous outflow stenosis) that confer higher rupture risk even after apparent cure. The objective of this study is to evaluate the feasibility and efficacy of 4D Flow MRI to quantitatively assess the hemodynamic changes in pediatric bAVMs following treatment and its use for early detection of high-risk changes. Methods: We have prospectively enrolled 20 children (mean age 11.8 ± 3.8 years) with bAVM into a single center cohort study. 4D Flow MRI was acquired in a transverse slab covering the circle of Willis using prospective gating, compressed sensing, and a resolution of 0.7 x 0.7 x 1.0 mm 3 on a 3T GE Discovery MR750 scanner. MRI at baseline and post-intervention (6-month and 1-year follow up) has been acquired for 5 patients thus far. 4D Flow data was post-processed by segmenting the main cerebral arteries and calculating cardiac-averaged flow rates in cross-sections orthogonal to the centerline of each vessel segment. Results: The flow rate accuracy was evaluated by calculating the flow conservation at the right/left internal carotid and basilar junctions, yielding average errors of 10.7% ± 12.7, 14.0% ± 9.5, and 19.3% ± 13.8 respectively. The hemisphere containing the bAVM received an average of 57.2% ± 2.8 of total brain flow at baseline, which decreased to an average of 51.2% ± 2.9 1-year follow-up. In 2 of 5 patients, the flow laterality between hemispheres flipped post-intervention with increased flow to the contralateral hemisphere. In all the post-intervention studies, we observed a decrease in flow and maximum velocities, as well as an increase in pulsatility index, in the primary feeding arteries to the bAVM (Figure). Conclusion: These preliminary results indicate that 4D Flow MRI may be a robust and useful tool for monitoring changes in intracranial flow patterns after bAVM treatment in children.

Transcranial Doppler Investigation of Hemodynamic Alterations Associated With Blunt Cervical Vascular Injuries in Trauma Patients

Blunt cervical vascular injuries, often missed with current screening methods, have substantial morbidity and mortality, and there is a need for improved screening. Elucidation of cerebral hemodynamic alterations may facilitate serial bedside monitoring and improved management. Thus, the objective of this study was to define cerebral flow alterations associated with single blunt cervical vascular injuries using transcranial Doppler sonography and subsequent Doppler waveform analyses in a trauma population. In this prospective pilot study, patients with suspected blunt cervical vascular injuries had diagnoses by computed tomographic angiography and were examined using transcranial Doppler sonography to define cerebral hemodynamics. Multiple vessel injuries were excluded for this analysis, as the focus was to identify hemodynamic alterations from isolated injuries. The inverse damping factor characterized altered extracranial flow patterns; middle cerebral artery flow velocities, the pulsatility index, and their asymmetries characterized altered intracranial flow patterns. Twenty-three trauma patients were evaluated: 4 with single internal carotid artery injuries, 5 with single vertebral artery injuries, and 14 without blunt cervical vascular injuries. All internal carotid artery injuries showed a reduced inverse damping factor in the internal carotid artery and dampened ipsilateral mean flow and peak systolic velocities in the middle cerebral artery. Vertebral artery injuries produced asymmetry of a similar magnitude in the middle cerebral artery mean flow velocity with end-diastolic velocity alterations. These data indicate that extracranial and intracranial hemodynamic alterations occur with internal carotid artery and vertebral artery blunt cervical vascular injuries and can be quantified in the acute injury phase by transcranial Doppler indices. Further study is required to elucidate cerebral flow changes resulting from a single blunt cervical vascular injury, which may guide future management to preserve cerebral perfusion after trauma.

E-080 4D-Flow MRI quantifies hemodynamics in large and giant intracranial aneurysms

PurposeUnruptured intracranial aneurysms (IA) are potentially life threatening conditions. Rupture risk based on specific data regarding interval growth or destabilization is lacking. We studied the feasibility of 4D-Flow MRI to...

Transcranial Doppler ultrasonography to confirm brain death: a meta-analysis

Barbiturate therapy or hypothermia precludes proper diagnosis of brain death either clinically or by EEG. Specific intracranial flow patterns indicating cerebral circulatory arrest (CCA) can be visualized by transcranial Doppler ultrasonography (TCD). The aim of this study was to assess the validity of TCD in confirming brain death. Meta-analysis of studies assessing the validity of TCD in confirming brain death. A systematic review of articles in English on the diagnosis brain death by TCD, published between 1980 and 2004, was performed. An oscillating or reverberating flow and systolic spikes were considered to be compatible with CCA. The quality of each study was assessed using standardized methodological criteria. The literature was searched for any article reporting a false-positive result. Two high-quality and eight low-quality studies were included. Meta-analysis of the two high-quality studies showed a sensitivity of 95% (95% CI 92-97%) and a specificity of 99% (95% CI 97-100%) to detect brain death. Meta-analysis of all ten studies showed a sensitivity of 89% and a specificity of 99%. In the literature we found two false-positive results; however, in both patients brain-stem function did show brain death shortly thereafter. CCA by TCD in the anterior and posterior circulation predicted fatal brain damage in all patients; therefore, TCD can be used to determine the appropriate moment for angiography. Further research is needed to demonstrate that CCA by TCD on repeated examination can also predict brain death in all patients.

Do brief bursts of spike and wave activity cause a cerebral hyper- or hypoperfusion in man?

The correlation between brain activity and cerebral blood flow velocities during brief bursts of generalized spike and wave activity was analysed by simultaneous registration of the EEG and the intracranial flow patterns. The flow patterns of the middle cerebral artery were continuously recorded by means of transcranial Doppler ultrasonography using a specially developed monitoring system. A total of 25 bursts was investigated in 3 patients with spontaneous occurrence of generalized 3 Hz spike and wave activity and normal background EEG. Characteristic changes of the flow patterns were found in all cases: 3.41 ± 0.98 s ( n = 25) after the beginning of generalized spike and wave patterns, the flow velocity decreased by 25.84 ± 10.45% ( n = 25) below the ‘preictal’ flow velocity level. The period of flow velocity changes lasted several times longer than the phase of spike and wave activity.

Dynamics of regional cerebral blood flow for various visual stimuli.

Isotope tracer methods for measuring regional cerebral blood flow or metabolism do not provide data on the dynamics of the fast adjustment of local cerebral blood flow. Measuring intracranial flow patterns of the posterior cerebral artery by means or 2 MHz pulsed transcranial Doppler ultrasonography demonstrated that detailed dynamic effects of various visual patterns on local cerebral perfusion can be recorded, and that visual stimuli of different complexity as well as the strategy of stimulus perception cause distinct flow velocity changes in the occipital cortex involved in information processing. This type of on--line analysis may become a powerful tool for detecting fast autoregulatory mechanisms in relation to purely functional cerebral changes.

Color Doppler imaging of intracranial vessels in the neonate.

This study was performed to examine the effectiveness of color Doppler imaging (CDI) in demonstrating the neonatal intracranial vessels and altered intracranial flow patterns and to determine the optimal approach in imaging and intracranial vasculature. The study was conducted in two parts. First, 14 neonates were examined with CDI by using a standard approach through the anterior fontanel. Whenever possible, views through the posterior fontanel and the temporal bone were obtained also. The anterior cerebral, M1 segment of the middle cerebral, distal internal carotid, and basilar arteries were demonstrated consistently. Portions of the vertebral distal middle cerebral, and posterior cerebral arteries were frequently visualized. In the second part of the study, we examined 10 neonates who had undergone extracorporeal membrane oxygenation. In this group of patients, CDI was able to demonstrate occlusion of the right internal carotid artery and the reversal of flow through the ipsilateral A1 segment. Increased flow on the contralateral side and in the basilar artery was observed in several patients. The anterior fontanel approach was shown to be the most useful in identifying most of the major intracranial arteries and veins with CDI. In addition, the body weights and gestational ages of the neonates were found to significantly influence the success rate in visualizing the intracranial vasculature.

Intracranial Flow Patterns in Infants Undergoing Extracorporeal Membrane Oxygenation: Preliminary Observations with Doppler US

Intracranial Flow Patterns in Infants Undergoing Extracorporeal Membrane Oxygenation: Preliminary Observations with Doppler US

Evaluation of intracranial pressure from transcranial Doppler studies in cerebral disease.

The extent to which estimations of intracranial pressure can be derived from intracranial flow patterns was studied. The blood flow velocity in the middle cerebral artery was recorded with the EME TC 2-64 transcranial Doppler (TCD) device in 26 patients suffering from various severe cerebral diseases. Simultaneously the mean intracranial pressure (ICP) was measured by means of an epidural device. Arterial carbon-dioxide tensions were monitored by blood gas analysis. In all patients it was observed that the middle cerebral artery flow patterns changed distinctly when the ICP increased; these changes were distinguished by a decrease of the mean flow velocity and an increase of the Pourcelot index. A good correlation between the ICP and the flow parameters (especially the product mean systemic arterial pressure x Pourcelot index/mean flow velocity) was found in a select group of 13 patients, in whom comparable initial conditions existed and in whom additional parameters influencing the TCD recordings could be kept constant (r = 0.873; P less than 0.001).