Monitoring Of Cerebral Blood Flow Research Articles

Application of Arterial Spin Labelling in the Assessment of Ocular Tissues.

Arterial spin labelling (ASL) is a noninvasive magnetic resonance imaging (MRI) modality, capable of measuring blood perfusion without the use of a contrast agent. While ASL implementation for imaging the brain and monitoring cerebral blood flow has been reviewed in depth, the technique is yet to be widely used for ocular tissue imaging. The human retina is a very thin but highly stratified structure and it is also situated close to the surface of the body which is not ideal for MR imaging. Hence, the application of MR imaging and ASL in particular has been very challenging for ocular tissues and retina. That is despite the fact that almost all of retinal pathologies are accompanied by blood perfusion irregularities. In this review article, we have focused on the technical aspects of the ASL and their implications for its optimum adaptation for retinal blood perfusion monitoring. Retinal blood perfusion has been assessed through qualitative or invasive quantitative methods but the prospect of imaging flow using ASL would increase monitoring and assessment of retinal pathologies. The review provides details of ASL application in human ocular blood flow assessment.

Intraoperative trans-fontanellar cerebral ultrasonography in infants during cardiac surgery under cardiopulmonary bypass: an observational study.

This study was performed to evaluate the feasibility of intraoperative point-of-care trans-fontanellar cerebral ultrasonography (TFCU) to obtain blood flow velocity (BFV) reference values at the internal carotid arteries (ICAs) and peri-callosal part of the anterior cerebral artery (pACA) during pediatric cardiac surgery under cardiopulmonary bypass (CPB). TFCU was performed at three time points (after induction of anesthesia, during CPB, after CPB) in 35 infants. BFV was measured at both ICAs and pACA through the anterior fontanelle with an ultrasound sector probe. We divided patients into Group S (<5kg, n=16) and Group L (≥5kg, n=19) for comparisons according to weight. We also analyzed BFV in low cerebral regional oxygen saturation (rSO2) data. All measurements of the BFV at both the ICAs and the pACA were possible. BFVs at the ICAs were lower in Group S than in Group L at all three time points. BFVs at the pACA were similar in both groups except higher value in Group L after CPB. When the rSO2 was <50, most BFVs (14 of 15 measurements) were lower than the median BFV value during CPB. However, a low rSO2 did not always reflect low BFV before and after CPB. Point-of-care TFCU can determine BFV at the ICAs and pACA during pediatric cardiac surgery. BFV differs according to the patient's size and CPB application. TFCU can be a practical cerebral blood flow monitoring method when rSO2 changes without any specific reason in infants.ClinicalTrials.gov NCT01996020.

Ultrasound tagged near infrared spectroscopy does not detect hyperventilation-induced reduction in cerebral blood flow

Introduction: Continuous non-invasive monitoring of cerebral blood flow (CBF) may be important during anaesthesia and several options are available. We evaluated the CerOx monitor that employs ultrasound tagged near infrared spectroscopy to estimate changes in a CBF index (CFI).Methods: Seven healthy males (age 21–26 years) hyperventilated and were administered phenylephrine to increase mean arterial pressure by 20–30 mmHg. Frontal lobe tissue oxygenation (ScO2) and CFI were obtained using the CerOx and mean blood flow velocity in the middle cerebral artery (MCAvmean) was determined by transcranial Doppler. Blood flow in the internal and external carotid artery (ICAf and ECAf) was determined using duplex ultrasonography and forehead skin blood flow (SkBF) and oxygenation (SskinO2) by laser Doppler and white light spectroscopy.Results: During hyperventilation MCAvmean and ICAf decreased by 44% (median; interquartile range 40–49; p = 0.016) and 46% (40–53; p = 0.03), respectively. Conversely, CFI increased by 9% (2–31; p = 0.016), while no significant change was observed in ScO2. SkBF increased by 19% (9–53; p = 0.016) and SskinO2 by 6% (1–7; p = 0.047), although ECAf was unchanged. Administration of phenylephrine was not associated with any changes in MCAvmean, ICAf, ECAf, ScO2, SkBF, SskinO2, or CFI.Conclusion: The CerOx was able to detect a stable CBF during administration of phenylephrine. However, during hyperventilation MCAvmean and ICAf decreased while CFI increased, likely due to an increase in superficial tissue oxygenation. Thus, CFI does not provide an unbiased evaluation of changes in CBF.

Dual-wavelength laser speckle imaging for monitoring brain metabolic and hemodynamic response to closed head traumatic brain injury in mice.

Abstract. The measurement of dynamic changes in brain hemodynamic and metabolism events following head trauma could be valuable for injury prognosis and for planning of optimal medical treatment. Specifically, variations in blood flow and oxygenation levels serve as important biomarkers of numerous pathophysiological processes. We employed the dual-wavelength laser speckle imaging (DW-LSI) technique for simultaneous monitoring of changes in brain hemodynamics and cerebral blood flow (CBF) at early stages of head trauma in a mouse model of intact head injury (n=10). For induction of head injury, we used a weight-drop device involving a metal mass (∼50 g ) striking the mouse’s head in a regulated manner from a height of ∼90 cm. In comparison to baseline measurements, noticeable dynamic variations were revealed immediately and up to 1 h postinjury, which indicate the severity of brain damage and highlight the ability of the DW-LSI arrangement to track brain pathophysiology induced by injury. To validate the monitoring of CBF by DW-LSI, measurements with laser Doppler flowmetry (LDF) were also performed (n=5), which confirmed reduction in CBF following injury. A secondary focus of the study was to investigate the effectiveness of hypertonic saline as a neuroprotective agent, inhibiting the development of complications after brain injury in a subgroup of injured mice (n=5), further demonstrating the ability of DW-LSI to monitor the effects upon brain dynamics of drug treatment. Overall, our findings further support the use of DW-LSI as a noninvasive, cost-effective tool to assess changes in hemodynamics under a variety of pathological conditions, suggesting its potential contribution to the biomedical field. To the best of our knowledge, this work is the first to make use of the DW-LSI modality in a small animal model to (1) investigate brain function during the critical first hour of closed head injury trauma, (2) correlate between injury parameters of LDF measurements, and (3) monitor brain hemodynamic and metabolic response to neuroprotective drug treatment.

Study of Risk Factors for Vascular Events in Sickle Cell Disease Traced By Neuroimaging and Trans Cranial Doppler Changes

Background : silent and overt stroke comprise10-20% of complication of sickle cell disease. There was great risk of morbidity and mortality, some time with neurocognitive dysfunctions Objective: to identify the most important risk factor for neurologic events using MRI and TCD as aid for diagnosis., Methodology: descriptive study carried out over one year period in al-zahraa hospital .thirty patients with sickle cell disease enrolled. All test done as part of follow up, which include ,serum ferritin, blood count, MRI, and TCD. Data was analyzed by using SSPS version 18. Results: of total 30 patients enrolled, only one patient found to have overt stroke, two other with silent strokeand 14 patient got abnormal TCD study. Most of CNS events found in patients with low hemoglobin (p value0.015), low red blood counts (p value 0.001), and those with high hemoglobin S concentration. Blood transfusionnoticed to be protective against stroke. Conclusion: risk of cerebral stroke was related to, severity of anemia ,high concentration of hemoglobin S Recommendations: regular monitoring of cerebral blood flow by TCD and MRI decreased morbidity andmortality, together with improvement in social, and conditional affairs of patients.

Acousto-Optic Cerebral Blood Flow Monitoring During Induction of Anesthesia in Humans.

Past transcranial Doppler (TCD) studies have documented the effects of the sequence of anesthesia induction followed by intubation on cerebral blood flow (CBF) velocity. The purpose of this study was to determine whether acousto-optic CBF monitoring would detect changes in CBF which are known to occur with propofol and subsequent endotracheal intubation. Seventy-two patients scheduled for elective non-intracranial surgery were evaluated. A Cerox 3215F (Ornim Medical) acousto-optic CBF monitor was used. The acousto-optic transducers were applied bifrontally prior to induction. Baseline cerebral flow index (CFI) values were obtained for at least 2min prior to induction, set to a unitless value of 100. Subsequent relative changes in CFI from baseline were determined at the lowest value over 3min after propofol injection but before laryngoscopy; and the highest value over 5min after the start of laryngoscopy. CFI data were evaluated using Friedman's test. The median dose of propofol [interquartile range] given was 200mg [160-250]. CFI decreased to 84% of baseline after propofol and increased to 147% of baseline after endotracheal intubation (both p<0.001); MAP decreased after intravenous induction of anesthesia from 103±15 to 86±15mmHg (p<0.001) and then returned following endotracheal intubation to 104±20mmHg. Our data are congruent with previous observations made with TCD under similar experimental conditions. Such observations support the notion that acousto-optic monitoring yields valid real-time measures of changes in CBF in humans. Further validation against other quantitative measures of CBF would be appropriate.

Pressure modulation algorithm to separate cerebral hemodynamic signals from extracerebral artifacts.

We introduce and validate a pressure measurement paradigm that reduces extracerebral contamination from superficial tissues in optical monitoring of cerebral blood flow with diffuse correlation spectroscopy (DCS). The scheme determines subject-specific contributions of extracerebral and cerebral tissues to the DCS signal by utilizing probe pressure modulation to induce variations in extracerebral blood flow. For analysis, the head is modeled as a two-layer medium and is probed with long and short source-detector separations. Then a combination of pressure modulation and a modified Beer-Lambert law for flow enables experimenters to linearly relate differential DCS signals to cerebral and extracerebral blood flow variation without a priori anatomical information. We demonstrate the algorithm's ability to isolate cerebral blood flow during a finger-tapping task and during graded scalp ischemia in healthy adults. Finally, we adapt the pressure modulation algorithm to ameliorate extracerebral contamination in monitoring of cerebral blood oxygenation and blood volume by near-infrared spectroscopy.

Real-time monitoring of cerebral blood flow by laser speckle contrast imaging after cardiac arrest in rat.

Cardiac arrest (CA) results in global brain ischemia. To explore the role of cerebral blood flow (CBF) during ischemia, laser speckle contrast imaging (LSCI), a full-field high-resolution optical imaging technique, was used for real-time monitoring of the fluctuations of CBF in a rat model of asphyxial-CA. The temporal changes of CBF were characterized and the relationship between CBF and mean arterial pressure (MAP) was evaluated. Asphyxial-CA led to transient CBF dysregulation, manifested by changes in CBF velocity were significantly impacted by MAP. Hyperemia is aligned with a bolus injection of vecuronium, the first two minutes of asphyxia, the time of epinephrine injection and cardiopulmonary resuscitation, and then lasted for 13 min after the return of spontaneous respiratory (ROSC), followed by hypoperfusion about 55-70% of baseline level no later than 40 min after ROSC. Interestingly, we found that the velocity of venule blood flow increased more than that of the arteriole blood flow during the hyperemia (176% vs 120%). Our study, for the first time, shows real-time CBF changes during and immediately after asphyxial-CA, with high spatial and temporal resolution images. The quantified cerebro-vascular response during the different phases of recovery after CA may underlie the mechanism of injury and recovery after brain ischemia. The study provides a new technique to study the neurovascular coupling and metabolic regulation of CBF after CA.

The Presto 1000: A novel automated transcranial Doppler ultrasound system

We examined the reliability and ease of use of a novel automated transcranial Doppler (TCD) system in comparison to a conventional TCD system. TCD ultrasound allows non-invasive monitoring of cerebral blood flow, and can predict arterial vasospasm after a subarachnoid hemorrhage (SAH). The Presto 1000 TCD system (PhysioSonics, Bellevue, WA, USA) is designed for monitoring flow through the M1 segment of the middle cerebral artery (MCA) via temporal windows. The Presto 1000 system was tested across multiple preclinical and clinical settings in parallel with a control predicate TCD system. In a phantom flow generating device, both the Presto 1000 and Spencer system (Spencer Technologies, Redmond, WA, USA) were able to detect velocities with high accuracy. In nine volunteer patients, the Presto system was able to locate the MCA in 14 out of 18 temporal windows, in an average of 12.5s. In the SAH cohort of five patients with a total of 25 paired measurements, the mean absolute difference in flow velocities of the M1 segment, as measured by the two systems, was 17.5cm/s. These data suggest that the Presto system offers an automated TCD that can reliably localize and detect flow of the MCA, with relative ease of use. The system carries the additional benefit of requiring minimal training for the operator, and can be used by many providers across multiple bedside settings. The mean velocities that were generated warrant further validation across an extended group of patients, and the predictive value for vasospasm should be checked against the current standard of angiography.

Histogram analysis of laser speckle contrast image for cerebral blood flow monitoring

Laser speckle contrast imaging (LSCI) is a powerful tool for blood flow mapping. In this paper, we described a simple algorithm based on histogram analysis of laser speckle contrast image to provide rapid differentiation between macro- and microcirculations. The algorithm was successfully verified by the study of blood flow in rat cortex under functional activation.

Regional brain monitoring in the neurocritical care unit.

Regional multimodality monitoring has evolved over the last several years as a tool to understand the mechanisms of brain injury and brain function at the cellular level. Multimodality monitoring offers an important augmentation to the clinical exam and is especially useful in comatose neurocritical care patients. Cerebral microdialysis, brain tissue oxygen monitoring, and cerebral blood flow monitoring all offer insight into permutations in brain chemistry and function that occur in the context of brain injury. These tools may allow for development of individual therapeutic strategies that are mechanistically driven and goal-directed. We present a summary of the discussions that took place during the Second Neurocritical Care Research Conference regarding regional brain monitoring.

Abstract W MP96: Low Dose Tissue Plasminogen Activator Amplifies Vascular Injury and Worsens Functional Outcomes in Acute Hyperglycemic Stroke Independent of the Model of Reperfusion

Clinically, hyperglycemia (HG) exacerbates reperfusion injury and aggravates tPA-induced hemorrhagic transformation (HT). Yet, most of the experimental hyperglycemic stroke studies exclusively employed suture occlusion model. Only few studies involved tPA in hyperglycemic setting and employed a 10-fold higher dose of tPA than that is used in patients. Thus, in this translational study using suture and thromboembolic occlusion of middle cerebral artery (MCA), with and without human tPA dose, we tested the hypothesis that even acute mild HG worsens the neurovascular injury and functional outcomes irrespective of the method of reperfusion, and that the use of low dose tPA amplifies this injury. Methods: Control and mildly HG rats (140-200 mg/dl, achieved by 30% glucose ip injection 15 min prior to surgery, n=7-9/group) were subjected to MCA occlusion by either suture (90 min) or humanized clot and 24 h reperfusion. tPA (1mg/kg) was injected IV 2 h after induction of ischemia. At 24 h, neurological deficit, infarct size, edema, HT occurrence rate (HT index) and tissue hemoglobin (Hb) were measured. Results: Cerebral blood flow monitoring indicated that % drop at occlusion were similar across the groups and that low dose tPA effectively resolved the clot in the embolic model. tPA did not increase the infarct size in either control or hyperglycemic animals when compared to no tPA groups (Table). HG increased vascular injury (HT index and Hb content) in both suture and embolic occlusion models. The combination of HG and tPA exacerbated the vascular injury and worsened functional outcomes more than each alone. Conclusion: The interaction between HG and even low dose tPA has a significant deleterious effect on cerebrovasculature and functional outcomes independent of the method of reperfusion.

Extended Doppler monitoring of cerebral blood flow in different subtypes of ischemic stroke

The dynamics of cerebral blood flow in acute ischemic stroke was studied with allowance for a pathogenic classification of stroke. Analysis of the ultrasound parameters demonstrated that particular attention should be given to quantitative, rather than qualitative, parameters of blood flow. The dynamics of cerebral blood flow in different etiologies of cerebral stroke is reflected in specific changes in the linear velocities, which relates a stroke subtype to the factors determining the need for extended monitoring. Clinical and instrumental assessment of the development of hemodynamic disorders during reperfusion after stroke by means of Doppler ultrasound demonstrated that, depending on the etiology of ischemic stroke, recovery of the intracerebral hemodynamics parameters to normal values occurs differently and has its features that, if timely detected, may affect correction of the strategy and tactics of treatment. Based on these data, we suggest a differentiated algorithm of extended Doppler monitoring of cerebral blood flow in acute ischemic stroke.

Cerebral oxygenation in health and disease.

Monitoring cerebral blood flow (CBF) and oxygenation has implications for both clinical practice and research interests; e.g., to provide insight into functional neurovascular coupling, to better understand orthostatic hypotension, and to evaluate the influence of vasopressors on cerebral oxygenation during anesthesia and/or surgery. These topics, and others, are addressed in this e-book by presenting original research, reviews, and opinion papers covering new, exciting but also controversial issues related to cerebral oxygenation in health and disease as evaluated by near-infrared spectroscopy (NIRS).

PO-0477 Targeted Cerebral Perfusion As Basic Strategy For Neonatal Intensive Care

Background and aims Target goals of haemodynamic support in critically ill newborns still remain unclear. Routine methods have some imperfection. NIRS attracts attention for neonatal intensive care. NIRS can reflect low oxygen delivery to the brain tissue but can’t distinguish between hypoxia and ischemia. Doppler evaluation of cerebral blood flow in anterior cerebral artery in addition to NIRS could pick out proper ischemia and clarify using of haemodynamic support and/or oxygen supply. Methods To evaluate relations between NIRS, Doppler cerebral blood flow and haemodynamic parameters we have obtained parallel recording of trends in six term babies with severe HIE. Results The records of trends for one of babies are exemplified. Respiratory support values were stable and SpO 2 was 99–100% using room air during all the period of observation. Conclusion A combination of NIRS monitoring and Doppler evaluation of cerebral blood flow is highly sensitive and could be used as a targeted parameter for neonatal intensive care. Considering rSO 2 more depends on circulatory sufficiency then FiO 2 it is expedient to use such a definition as ‘oxygenous price of saturation’. In that case using of Doppler estimation of cerebral blood flow pattern allows differing mixed hypoxia and cerebral ischemia aiming to choose proper ways of intensive care.

Induction and imaging of photothrombotic stroke in conscious and freely moving rats.

In experimental stroke research, anesthesia is common and serves as a major reason for translational failure. Real-time cerebral blood flow (CBF) monitoring during stroke onset can provide important information for the prediction of brain injury; however, this is difficult to achieve in clinical practice due to various technical problems. We created a photothrombotic focal ischemic stroke model utilizing our self-developed miniature headstage in conscious and freely moving rats. In this model, a high spatiotemporal resolution imager using laser speckle contrast imaging technology was integrated to acquire real-time two-dimensional CBF information during thrombosis. The feasibility, stability, and reliability of the system were tested in terms of CBF, behavior, and T2-weighted magnetic resonance imaging (MRI) findings. After completion of occlusion, the CBF in the targeted cortex of the stroke group was reduced to 16 ± 9% of the baseline value. The mean infarct volume measured by MRI 24 h postmodeling was 77 ± 11 mm3 and correlated well with CBF (R2 = 0.74). This rodent model of focal cerebral ischemia and real-time blood flow imaging opens the possibility of performing various fundamental and translational studies on stroke without the influence of anesthetics.

Monitoring of cerebral blood flow and ischemia in the critically ill.

Secondary ischemic injury is common after acute brain injury and can be evaluated with the use of neuromonitoring devices. This manuscript provides guidelines for the use of devices to monitor cerebral blood flow (CBF) in critically ill patients. A Medline search was conducted to address essential pre-specified questions related to the utility of CBF monitoring. Peer-reviewed recommendations were constructed according to the GRADE criteria based upon the available supporting literature. Transcranial Doppler ultrasonography (TCD) and transcranial color-coded duplex sonography (TCCS) are predictive of angiographic vasospasm and delayed ischemic neurological deficits after aneurysmal subarachnoid hemorrhage. TCD and TCCS may be beneficial in identifying vasospasm after traumatic brain injury. TCD and TCCS have shortcomings in identifying some secondary ischemic risks. Implantable thermal diffusion flowmetry (TDF) probes may provide real-time continuous quantitative assessment of ischemic risks. Data are lacking regarding ischemic thresholds for TDF or their correlation with ischemic injury and clinical outcomes.TCD and TCCS can be used to monitor CBF in the neurocritical care unit. Better and more developed methods of continuous CBF monitoring are needed to limit secondary ischemic injury in the neurocritical care unit.

PGD2 DP1 receptor stimulation following stroke ameliorates cerebral blood flow and outcomes

Stroke is a leading cause of death and morbidity worldwide, yet effective treatments are lacking. The association of prostaglandin D2 and its DP1 receptor with vasculature and blood propelled us to examine whether the clinically tested DP1 receptor agonist BW245C had beneficial effects following stroke. To determine if BW245C affects basal cerebral blood flow (CBF), C57BL/6 WT and DP1−/− mice were given a single i.p. injection of vehicle or BW245C, and CBF was recorded for 2h. To test the effect of BW245C on stroke, WT and DP1−/− mice were subjected to middle cerebral artery occlusion followed by a single i.p. injection of vehicle or 0.02, 0.2, or 2.0-mg/kg BW245C immediately before reperfusion. Functional and anatomical outcomes were determined at 96h. We also determined the effect of BW245C on CBF in peri-infarct and core during occlusion and reperfusion. Furthermore, we tested the effect of BW245C on bleeding time and ex vivo coagulation. BW245C treatment increased the basal CBF significantly in WT but not in DP1−/− mice. The BW245C treatment also significantly improved functional outcome and lowered infarction volume. The multisite CBF monitoring by laser-Doppler flowmetry shows that BW245C significantly increased the CBF in peri-infarct, with a significant inverse correlation between infarction and CBF. The significantly higher infarction volume in DP1−/− mice remained unchanged with BW245C treatment. Moreover, BW245C preserves hemostasis in non-stroke conditions. Combined, these data suggest that the DP1 receptor is an endogenous target that can rescue the brain following stroke by regulating CBF and hemostasis.

Intraoperative cerebral blood flow imaging of rodents.

Intraoperative monitoring of cerebral blood flow (CBF) is of interest to neuroscience researchers, which offers the assessment of hemodynamic responses throughout the process of neurosurgery and provides an early biomarker for surgical guidance. However, intraoperative CBF imaging has been challenging due to animal's motion and position change during the surgery. In this paper, we presented a design of an operation bench integrated with laser speckle contrast imager which enables monitoring of the CBF intraoperatively. With a specially designed stereotaxic frame and imager, we were able to monitor the CBF changes in both hemispheres during the rodent surgery. The rotatable design of the operation plate and implementation of online image registration allow the technician to move the animal without disturbing the CBF imaging during surgery. The performance of the system was tested by middle cerebral artery occlusion model of rats.

Intraoperative laser speckle contrast imaging with retrospective motion correction for quantitative assessment of cerebral blood flow.

Although multiple intraoperative cerebral blood flow (CBF) monitoring techniques are currently available, a quantitative method that allows for continuous monitoring and that can be easily integrated into the surgical workflow is still needed. Laser speckle contrast imaging (LSCI) is an optical imaging technique with a high spatiotemporal resolution that has been recently demonstrated as feasible and effective for intraoperative monitoring of CBF during neurosurgical procedures. This study demonstrates the impact of retrospective motion correction on the quantitative analysis of intraoperatively acquired LSCI images. LSCI images were acquired through a surgical microscope during brain tumor resection procedures from 10 patients under baseline conditions and after a cortical stimulation in three of those patients. The patient's electrocardiogram (ECG) was recorded during acquisition for postprocess correction of pulsatile artifacts. Automatic image registration was retrospectively performed to correct for tissue motion artifacts, and the performance of rigid and nonrigid transformations was compared. In baseline cases, the original images had [Formula: see text] noise across 16 regions of interest (ROIs). ECG filtering moderately reduced the noise to [Formula: see text], while image registration resulted in a further noise reduction of [Formula: see text]. Combined ECG filtering and image registration significantly reduced the noise to [Formula: see text] ([Formula: see text]). Using the combined motion correction, accuracy and sensitivity to small changes in CBF were improved in cortical stimulation cases. There was also excellent agreement between rigid and nonrigid registration methods (15/16 ROIs with [Formula: see text] difference). Results from this study demonstrate the importance of motion correction for improved visualization of CBF changes in clinical LSCI images.