Early postischemic hyperperfusion: pathophysiologic insights from positron emission tomography

Acute Ischemic Stroke in the Clinic and the Laboratory: Targets for Translational Research

Ischemic stroke research has enabled significant advancements in diagnosis, treatment, and management of this debilitating disease, yet challenges remain standing in the way of better patient prognoses. In this narrative review, a fictional case illustrates challenges and uncertainties that medical professionals still face - penumbra identification, lack of neuroprotective agents, side-effects of tissue plasminogen activator, dearth of molecular biomarkers, incomplete microvascular reperfusion or no-reflow, post-recanalization hyperperfusion, blood pressure management and procedural anesthetic effects. The current state of the field is broadly reviewed per topic, with the aim to introduce a broad audience (scientist and clinician alike) to recent successes in translational stroke research and pending scientific queries that are tractable for preclinical assessment. Opportunities for co-operation between clinical and experimental stroke experts are highlighted to increase the size and frequency of strides the field makes to improve our understanding of this disease and ways of treating it.

Implications of Post-recanalization Perfusion Deficit After Acute Ischemic Stroke: a Scoping Review of Clinical and Preclinical Imaging Studies

The goal of reperfusion therapy for acute ischemic stroke (AIS) is to restore cerebral blood flow through recanalization of the occluded vessel. Unfortunately, successful recanalization does not always result in favorable clinical outcome. Post-recanalization perfusion deficits (PRPDs), constituted by cerebral hypo- or hyperperfusion, may contribute to lagging patient recovery rates, but its clinical significance remains unclear. This scoping review provides an overview of clinical and preclinical findings on post-ischemic reperfusion, aiming to elucidate the pattern and consequences of PRPD from a translational perspective. The MEDLINE database was searched for quantitative clinical and preclinical studies of AIS reporting PRPD based on cerebral circulation parameters acquired by translational tomographic imaging methods. PRPD and stroke outcome were mapped on a charting table, creating an overview of PRPD after AIS. Twenty-two clinical and twenty-two preclinical studies were included. Post-recanalization hypoperfusion is rarely reported in clinical studies (4/22) but unequivocally associated with detrimental outcome. Post-recanalization hyperperfusion is more commonly reported (18/22 clinical studies) and may be associated with positive or negative outcome. PRPD has been replicated in animal studies, offering mechanistic insights into causes and consequences of PRPD and allowing delineation of possible courses of PRPD. Complex relationships exist between PRPD and stroke outcome. Diversity in methods and lack of standardized definitions in reperfusion studies complicate the characterization of reperfusion patterns. Recommendations are made to advance the understanding of PRPD mechanisms and to further disentangle the relation between PRPD and disease outcome.

Cerebral Ischemic Reperfusion Injury: Preventative and Therapeutic Strategies

Acute ischemic stroke is a leading cause of morbidity and mortality in the United States. Treatment goals remain focused on restoring blood flow to compromised areas. However, a major concern arises after reperfusion occurs. Cerebral ischemic reperfusion injury is defined as damage to otherwise salvageable brain tissue occurring with the reestablishment of the vascular supply to that region. The pool of eligible patients for revascularization continues to grow, especially with the recently expanded endovascular therapeutic window. Neurointensivists should understand and manage complications of successful recanalization. In this review, we examine the pathophysiology, diagnosis, and potential management strategies in cerebral ischemic reperfusion injury.

Persistent perfusion abnormalities at day 1 correspond to different clinical trajectories after stroke

BACKGROUND

Perfusion abnormalities after thrombolysis are frequent within and surrounding ischemic lesions, but their relative frequency is not well known.

OBJECTIVE

To describe the different patterns of perfusion abnormalities observed at 24 hours and compare the characteristics of the patients according to their perfusion pattern.

METHODS

From our thrombolysis registry, we included 226 consecutive patients with an available arterial spin labeling (ASL) perfusion sequence at day 1. We performed a blinded assessment of the perfusion status (hypoperfusion-h, hyperperfusion-H, or normal-N) in the ischemic lesion and in the surrounding tissue. We compared the time course of clinical recovery, the rate of arterial recanalization, and hemorrhagic transformations in the different perfusion profiles.

RESULTS

We identified seven different perfusion profiles at day 1. Four of these (h/h, h/H, H/H, and H/N) represented the majority of the population (84.1%). The H/H profile was the most frequent (34.5%) and associated with 3-month good outcome (modified Rankin Scale (mRS): 63.5%). Patients with persistent hypoperfusion within and outside the lesion (h/h, 12.4%) exhibited worse outcomes after treatment (mRS score 0-2: 23.8%) than other patients, were less frequently recanalized (40.7%), and had more parenchymal hematoma (17.8%). The h/H profile had an intermediate clinical trajectory between the h/h profile and the hyperperfused profiles.

CONCLUSION

ASL hypoperfusion within the infarct and the surrounding tissue was associated with poor outcome. A more comprehensive view of the mechanisms in the hypoperfused surrounding tissue could help to design new therapeutic approaches during and after reperfusion therapies.

Pictorial Review on Imaging Findings in Cerebral CTP in Patients with Acute Stroke and Its Mimics: A Primer for General Radiologists

The imaging evaluation of computed tomography (CT), CT angiography (CTA), and CT perfusion (CTP) is of crucial importance in the setting of each emergency department for suspected cerebrovascular impairment. A fast and clear assignment of characteristic imaging findings of acute stroke and its differential diagnoses is essential for every radiologist. Different entities can mimic clinical signs of an acute stroke, thus the knowledge and fast identification of stroke mimics is important. A fast and clear assignment is necessary for a correct diagnosis and a rapid initiation of appropriate therapy. This pictorial review describes the most common imaging findings in CTP with clinical signs for acute stroke or other acute neurological disorders. The knowledge of these pictograms is therefore essential and should also be addressed in training and further education of radiologists.

Neuroimaging of Acute Ischemic Stroke: Multimodal Imaging Approach for Acute Endovascular Therapy

Advances in acute ischemic stroke (AIS) treatment have been contingent on innovations in neuroimaging. Neuroimaging plays a pivotal role in the diagnosis and prognosis of ischemic stroke and large vessel occlusion, enabling triage decisions in the emergent care of the stroke patient. Current imaging protocols for acute stroke are dependent on the available resources and clinicians' preferences and experiences. In addition, differential application of neuroimaging in medical decision-making, and the rapidly growing evidence to support varying paradigms have outpaced guideline-based recommendations for selecting patients to receive intravenous or endovascular treatment. In this review, we aimed to discuss the various imaging modalities and approaches used in the diagnosis and treatment of AIS.

MRI investigation of vascular remodeling for heterogeneous edema lesions in subacute ischemic stroke rat models: Correspondence between cerebral vessel structure and function

The spatial heterogeneity in the temporal occurrence of pseudo-normalization of MR apparent diffusion coefficient values for ischemic lesions may be related to morphological and functional vascular remodeling. As the area of accelerated pseudo-normalization tends to expand faster and more extensively into the chronic stage, detailed vascular characterization of such areas is necessary. During the subacute stage of transient middle cerebral artery occlusion rat models, the morphological size of the macrovasculature, microvascular vessel size index (VSI), and microvessel density (MVD) were quantified along with functional perfusion measurements of the relative cerebral blood flow (rCBF) and mean transit time (rMTT) of the corresponding areas (33 cases for each parameter). When compared with typical pseudo-normalization lesions, early pseudo-normalization lesions exhibited larger VSI and rCBF (p < 0.001) at reperfusion days 4 and 7, along with reduced MVD and elongated rMTT (p < 0.001) at reperfusion days 1, 4, and 7. The group median VSI and rCBF exhibited a strong positive correlation (r = 0.92), and the corresponding MVD and rMTT showed a negative correlation (r = -0.48). Light sheet fluorescence microscopy images were used to quantitatively validate the corresponding MRI-derived microvascular size, density, and cerebral blood volume.

A novel wireless optical technique for quantitative evaluation of cerebral perfusion pressure in a fluid percussion animal model of traumatic brain injury

Background

Cerebral perfusion pressure (CPP) calculated by mean arterial pressure (MAP) minus intracranial pressure (ICP) is related to blood flow into the brain and reflects cerebral ischemia and oxygenation indirectly. Near-infrared spectroscopy (NIRS) can assess cerebral ischemia and hypoxia non-invasively and has been widely used in neuroscience. However, the correlation between CPP and NIRS, and its potential application in traumatic brain injury, has seldom been investigated.

Methods

We used a novel wireless NIRS system and commercial ICP and MAP devices to assess the trauma to rat brains using different impact intensity. The relationship between CPP and NIRS parameters with increasing impact strength were investigated.

Results

The results showed that changes in CPP (∆CPP), oxy-hemoglobin {∆[HbO₂]}, total-hemoglobin {∆[HbT]}, and deoxy-hemoglobin were inversely proportional to the increase in impact intensity, and the correlations between ∆CPP, NIRS parameters {∆[HbO₂], and ∆[HbT]} were significant.

Conclusions

The NIRS system can assess cerebral ischemia and oxygenation non-invasively and changes of HbO₂ and HbT may be used as reference parameters to assess the level of CPP in an animal model of traumatic brain injury.

Temporal Changes in Brain Perfusion in Neuronal Intranuclear Inclusion Disease

We herein report a patient with neuronal intranuclear inclusion disease (NIID) who presented with encephalitis-like episodes. A neurological examination revealed a disturbance of consciousness without any evidence of encephalitis or epilepsy on laboratory tests. Brain perfusion single-photon emission computed tomography revealed an elevated cerebral blood flow during the encephalitis-like episode and reduced cerebral blood flow in the chronic phase with clinical recovery. This report suggests that the cerebral blood flow of patients with NIID can change over the clinical course. Encephalitis-like episodes of NIID should thus be considered in the differential diagnosis of acute disturbance of consciousness.

Acute Brain Stroke Evolution Detected by 18F-FDG PET/CT and MRI Justifies the Discordance of Lesions in a Patient With Lymphoproliferative Syndrome

ABSTRACT

A 50-year-old man with angioimmunoblastic T-cell lymphoma in complete response to treatment presented new hypermetabolic brain lesions on 18F-FDG PET/CT suggestive of malignancy. These findings were correlated by MRI that showed cortical-subcortical peripheral lesions typical of acute ischemic infarction. A restaging 18F-FDG PET/CT showed that hypermetabolic lesions were replaced by ametabolic areas, supporting chronic infarction. Early ischemia presents transitory FDG increase. Brain lymphomas are highly FDG avid and difficult to differentiate from acute cerebral infarction. In view of the discordance of abnormal areas of intracranial uptake on PET FDG, MRI confirmation is required to avoid misinterpretation.

Combined Perfusion and Permeability Imaging Reveals Different Pathophysiologic Tissue Responses After Successful Thrombectomy

Despite successful recanalization of large-vessel occlusions in acute ischemic stroke, individual patients profit to a varying degree. Dynamic susceptibility-weighted perfusion and dynamic T1-weighted contrast-enhanced blood-brain barrier permeability imaging may help to determine secondary stroke injury and predict clinical outcome. We prospectively performed perfusion and permeability imaging in 38 patients within 24 h after successful mechanical thrombectomy of an occlusion of the middle cerebral artery M1 segment. Perfusion alterations were evaluated on cerebral blood flow maps, blood-brain barrier disruption (BBBD) visually and quantitatively on k_trans maps and hemorrhagic transformation on susceptibility-weighted images. Visual BBBD within the DWI lesion corresponded to a median k_trans elevation (IQR) of 0.77 (0.41–1.4) min⁻¹ and was found in all 7 cases of hypoperfusion (100%), in 10 of 16 cases of hyperperfusion (63%), and in only three of 13 cases with unaffected perfusion (23%). BBBD was significantly associated with hemorrhagic transformation (p < 0.001). While BBBD alone was not a predictor of clinical outcome at 3 months (positive predictive value (PPV) = 0.8 [0.56–0.94]), hypoperfusion occurred more often in patients with unfavorable clinical outcome (PPV = 0.43 [0.10–0.82]) compared to hyperperfusion (PPV = 0.93 [0.68–1.0]) or unaffected perfusion (PPV = 1.0 [0.75–1.0]). We show that combined perfusion and permeability imaging reveals distinct infarct signatures after recanalization, indicating the severity of prior ischemic damage. It assists in predicting clinical outcome and may identify patients at risk of stroke progression.

Angiographic early hyperemia in the middle cerebral artery territory after thrombectomy is associated with favorable clinical outcome in anterior circulation stroke

OBJECTIVES

Angiographic cortical early hyperemia (EH) is frequently observed after endovascular thrombectomy (EVT) for large vessel occlusion (LVO) stroke. The aim of the study is to investigate the relationship between EH and clinical outcomes.

METHODS

Between January 2015 and September 2018, consecutive patients who underwent EVT for anterior circulation LVO stroke with optimal recanalization (modified thrombolysis in cerebral infarction 2b or 3) were included. Angiographic studies after immediate reperfusion were used for analysis for cortical EH sign. Clinical functional outcomes were evaluated with the modified Rankin Scale (mRS) at 90 days. Safety outcomes, including mortality and intracerebral hemorrhage, were assessed. The association of EH between clinical functional and safety outcomes was analyzed.

RESULTS

A total of 143 patients were analyzed (mean age: 71 years; median National Institutes of Health Stroke Scale score: 18). A positive EH sign was observed in 88 (62%) patients. Good functional outcome at 90 days was significantly different between the EH⁺ and EH^- groups (p = .0157). Intracerebral hemorrhage and mortality did not differ between groups. In multivariate logistic regression analysis, EH was an independent predictor for good clinical outcome (mRS ≤ 2, odds ratio: 3.49, p = .0034) in addition to young age.

CONCLUSION

Results revealed that the presence of EH is associated with better clinical outcome at 90 days, but not associated with increased hemorrhagic complication. These findings with clinically relevant implications require further validation.

KEY POINTS

• Angiographic cortical hyperemia is a common finding immediately after endovascular thrombectomy. • Presence of cortical hyperemia is an independent prognostic factor for good clinical outcome. • Hemorrhagic complication is not associated with cortical hyperemia.

Hyperperfusion on Arterial Spin Labeling MRI Predicts the 90-Day Functional Outcome After Mechanical Thrombectomy in Ischemic Stroke

BACKGROUND

The prognostic significance of hyperperfusion after reperfusion therapy in patients with acute ischemic stroke (AIS) remains controversial.

PURPOSE

To investigate the clinical factors associated with hyperperfusion, and the 90-day prognostic value of hyperperfusion after mechanical thrombectomy in AIS patients.

STUDY TYPE

Retrospective.

POPULATION/SUBJECTS

Fifty-four AIS patients who underwent mechanical thrombectomy.

FIELD STRENGTH/SEQUENCE

Time-of-flight MR angiography, pulsed arterial spin labeling (ASL), diffusion-weighted imaging (DWI), and susceptibility-weighted imaging were performed at 3.0T within 1 week after thrombectomy.

ASSESSMENT

Clinical factors including demographics, risk factors, stroke and treatment characteristics were collected and assessed. Hyperperfusion on ASL was defined as a focal increased cerebral blood flow on the affected side ≥130% of its mirror counterpart. Good clinical outcome at 90 days was defined as modified Rankin Scale score of 0-2.

STATISTICAL TESTS

The interrater agreement was assessed using Cohen's kappa or the intraclass correlation coefficient. The relationship between hyperperfusion and clinical factors were analyzed by appropriate univariate statistics. Predictors of 90-day functional outcome were assessed by univariate analyses followed by multivariate logistic regression analysis and receiver-operating-characteristic curves.

RESULTS

Thirty-six (66.7%) patients developed hyperperfusion on ASL after thrombectomy. Hyperperfusion was significantly correlated with successful recanalization (P < 0.05) and improvement of National Institutes of Health Stroke Scale scores at 24 hours (NIHSS_24h ) (P < 0.05). A higher incidence of hemorrhage transformation was observed in patients with hyperperfusion than those without (63.9% vs. 50.0%), but no significant difference was found (P = 0.327). NIHSS_24h (odds ratio [OR], 0.75, [95% confidence interval [CI] 0.62-0.91], P < 0.05), lesion volume on diffusion-weighted imaging (OR, 0.97, [95% CI 0.95-1.00], P < 0.05), and hyperperfusion on ASL (OR, 9.8, [95% CI 1.7-55.3], P < 0.05) were independent variables for predicting good functional outcomes.

DATA CONCLUSION

Hyperperfusion on ASL correlated with successful recanalization and may be an independent prognostic marker for good neurological outcomes at 90 days in AIS patients after mechanical thrombectomy.

LEVEL OF EVIDENCE

4 TECHNICAL EFFICACY STAGE: 2.

Early-stage 11C-Flumazenil PET predicts day-14 selective neuronal loss in a rodent model of transient focal cerebral ischemia

Predicting tissue outcome early after stroke is an important goal. MRI >3 h accurately predicts infarction but is insensitive to selective neuronal loss (SNL). Previous studies suggest that chronic-stage ¹¹C-flumazenil PET (FMZ-PET) is a validated marker of SNL in rats, while early-stage FMZ-PET may predict infarction. Whether early FMZ-PET also predicts SNL is unknown. Following 45-min distal MCA occlusion, adult rats underwent FMZ-PET at 1 h and 48 h post-reperfusion to map distribution volume (V_T), which reflects GABA-_A receptor binding. NeuN immunohistochemistry was performed at Day 14. In each rat, V_T and %NeuN loss were determined in 44 ROIs spanning the hemisphere. NeuN revealed isolated SNL and cortical infarction in five and one rats, respectively. In the SNL subgroup, V_T-1 h was mildly reduced and only weakly predicted SNL, while V_T-48 h was significantly increased and predicted SNL both individually (p < 0.01, Kendall) and across the group (p < 0.001), i.e. the higher the V_T, the stronger the SNL. Similar correlations were found in the rat with infarction. Our findings suggest GABA-_A receptors are still present on injured neurons at the 48 h timepoint, and the increased 48 h V_T observed here is consistent with earlier rat studies showing early GABA-_A receptor upregulation. That FMZ binding at 48 h was predictive of SNL may have clinical implications.

Cerebellar Blood Flow and Gene Expression in Crossed Cerebellar Diaschisis after Transient Middle Cerebral Artery Occlusion in Rats

Crossed cerebellar diaschisis (CCD) is a state of hypoperfusion and hypometabolism in the contralesional cerebellar hemisphere caused by a supratentorial lesion, but its pathophysiology is not fully understood. We evaluated chronological changes in cerebellar blood flow (CbBF) and gene expressions in the cerebellum using a rat model of transient middle cerebral artery occlusion (MCAO). CbBF was analyzed at two and seven days after MCAO using single photon emission computed tomography (SPECT). DNA microarray analysis and western blotting of the cerebellar cortex were performed and apoptotic cells in the cerebellar cortex were stained. CbBF in the contralesional hemisphere was significantly decreased and this lateral imbalance recovered over one week. Gene set enrichment analysis revealed that a gene set for “oxidative phosphorylation” was significantly upregulated while fourteen other gene sets including “apoptosis”, “hypoxia” and “reactive oxygen species” showed a tendency toward upregulation in the contralesional cerebellum. MCAO upregulated the expressions of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) in the contralesional cerebellar cortex. The number of apoptotic cells increased in the molecular layer of the contralesional cerebellum. Focal cerebral ischemia in our rat MCAO model caused CCD along with enhanced expression of genes related to oxidative stress and apoptosis.

Assessment of a Non-Invasive Brain Oximeter in a Sheep Model of Acute Brain Injury

Introduction

Evidence suggests treatments guided by brain oxygen levels improve patient outcomes following severe traumatic brain injury; however, brain oxygen levels are not routinely monitored as an effective non-invasive method has not been established. We undertook a study, in a sheep model of acute brain injury, to assess a new non-invasive brain oximeter. The monitor uses the principles of pulse oximetry to record a pulse and oxygen levels.

Methods

We studied 8 sheep. An acute increase in intracranial pressure was induced with an injection of blood into the cranial vault. The temporal changes in the brain oximeter, intracranial pressure and cerebral perfusion pressure were recorded. Simultaneous conventional skin pulse oximetry was also recorded to assess the possible influence of skin blood flow on the brain oximeter signal.

Results

At baseline, a pulsatile waveform consistent with the brain circulation was obtained in 7 animals. The baseline brain pulse was quite distinct from the simultaneous conventional skin pulse and similar in shape to a central venous pressure waveform. Injection of blood into the cranial vault triggered an immediate increase in intracranial pressure and fall in cerebral perfusion pressure, by 60-s cerebral perfusion pressure recovered. The brain oximeter oxygen levels demonstrated similar changes with an immediate fall and recovery by 60 s. Periods of high intracranial pressure were also associated with high-frequency oscillations in the brain pulse waveform; there was, however, no change in the conventional skin pulse oximeter pulse waveform.

Conclusion

The brain oximeter detected acute changes in both oxygen levels and the brain pulse waveform following an increase in intracranial pressure levels. The brain oximeter could assist clinicians in the management of acute brain injury.

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Cerebral Hemodynamic Evaluation After Cerebral Recanalization Therapy for Acute Ischemic Stroke

Cerebral recanalization therapy, either intravenous thrombolysis or mechanical thrombectomy, improves the outcomes in patients with acute ischemic stroke (AIS) by restoring the cerebral perfusion of the ischemic penumbra. Cerebral hemodynamic evaluation after recanalization therapy, can help identify patients with high risks of reperfusion-associated complications. Among the various hemodynamic modalities, magnetic resonance imaging (MRI), computed tomography perfusion, and transcranial Doppler sonography (TCD) are the most commonly used. Poststroke hypoperfusion is associated with infarct expansion, while hyperperfusion, which once was considered the hallmark of successful recanalization, is associated with hemorrhagic transformation. Either the hypo- or the hyperperfusion may result in poor clinical outcomes. Individual blood pressure target based on cerebral hemodynamic evaluation was crucial to improve the prognosis. This review summarizes literature on cerebral hemodynamic evaluation and management after recanalization therapy to guide clinical decision making.

Multispectral imaging of cortical vascular and hemodynamic responses to a shock wave: observation of spreading depolarization and oxygen supply-demand mismatch

Blast-induced traumatic brain injury has been a recent major concern in neurotraumatology. However, its pathophysiology and mechanism are not understood partly due to insufficient information on the brain pathophysiology during/immediately after shock wave exposure. We transcranially applied a laser-induced shock wave (LISW, ∼19  Pa  ·  s) to the left frontal region in a rat and performed multispectral imaging of the ipsilateral cortex through a cranial window (n  =  4). For the spectral data obtained, we conducted multiple regression analysis aided by Monte Carlo simulation to evaluate vascular diameters, regional hemoglobin concentration (rCHb), tissue oxygen saturation (StO2), oxygen extraction fraction, and light-scattering signals as a signature of cortical spreading depolarization (CSD). Immediately after LISW exposure, rCHb and StO2 were significantly decreased with distinct venular constriction. CSD was then generated and was accompanied by distinct hyperemia/hyperoxemia. This was followed by oligemia with arteriolar constriction, but it soon recovered (within ∼20  min). However, severe hypoxemia was persistently observed during the post-CSD period (∼1  h). These observations indicate that inadequate oxygen supply and/or excessive oxygen consumption continued even after blood supply was restored in the cortex. Such a hypoxemic state and/or a hypermetabolic state might be associated with brain damage caused by a shock wave.

Clinical outcome prediction after thrombectomy of proximal middle cerebral artery occlusions by the appearance of lenticulostriate arteries on magnetic resonance angiography: A retrospective analysis

Post-ischemic vasodynamic changes in infarcted brain parenchyma are common and range from hypo- to hyperperfusion. In the present study, appearance of the lenticulostriate arteries (LSAs) on postinterventional 3T time-of-flight (TOF)-MRA suggestive for altered post-stroke vasodynamics following thrombectomy was investigated. Patients who underwent thrombectomy for a proximal MCA occlusion and for whom postinterventional 3T TOF-MRA (median at day 3) was available, were included in this retrospective analysis (n=98). LSA appearance was categorized into presence (LSA-sign⁺) or absence (LSA-sign^-) of vasodilatation in the ischemic hemisphere. Functional outcome was determined using the modified Rankin scale (mRS). LSA-sign⁺ was observed in 64/98 patients. Hypertension (adjusted OR: 0.171, 95% CI: 0.046-0.645) and preinterventional IV rtPA (adjusted OR: 0.265, 95% CI: 0.088-0.798) were associated with absence of the LSA-sign⁺. In multivariate logistic regression, LSA-sign⁺ was associated with substantial neurologic improvement (adjusted OR: 10.18, 95% CI: 2.69-38.57) and good functional outcome (discharge-mRS ≤ 2, adjusted OR: 7.127, 95% CI: 1.913-26.551 and day 90 mRS ≤ 2, adjusted OR: 3.786, 95% CI: 1.026-13.973) after correcting for relevant confounders. For all clinical endpoints, model fit improved when including the LSA-sign term (p<0.05). Asymmetrical dilatation of LSAs following successful thrombectomy indicates favorable neurologic and mid-term functional outcomes. This may indicate preserved cerebral blood flow regulatory mechanisms.

Arterial Spin Labeling MRI to Measure Cerebral Blood Flow in Untreated Ischemic Stroke

BACKGROUND AND PURPOSE

This study aims to investigate the significance of regional hyperperfusion (RH) detected by arterial spin labeling (ASL) in a group of untreated stroke patients, within 24-36 hours after symptom onset. The relationship between RH volume and infarcted volume (DIV) as defined on diffusion weighted images (DWIs) was evaluated.

METHODS

Of the 346 consecutive acute stroke patients who attended our center, we retrospectively reviewed MRI studies of 47 patients who were ineligible for standard treatment with intravenous tissue plasminogen activator. The MRI study included ASL and DWI. The ASL-derived cerebral blood flow (CBF) maps were coregistered on the DWI images. RH volume and DIV were calculated and compared. Patient NIHSS scores were also evaluated at admission, discharge, and after 1 and 6-month follow-up.

RESULTS

Twenty-two patients showed RH with CBF twice than baseline. In all 22 patients, RH overlaps with DWI infarcted area. No significant difference (P = .94) between RH volume and DIV was found (7.2 ± 9.6 and 9.0 ± 11.9 cm³ ). The Pearson's correlation coefficient between RH and DIV was .93. On univariate analysis, a significant difference was found between patient's groups on NIHSS at any time points, after covariates adjustment NIHSS difference was significant only at admission.

CONCLUSIONS

The study showed that ASL perfusion could be an integral part of the MRI examination in the assessment of 24-36 hours not-treated stroke patients as sustained RH group had improved outcomes. More importantly, ASL perfusion may provide evidence of beneficial effects of reperfusion induced by recanalization treatment.

Focal ischemic stroke leads to lung injury and reduces alveolar macrophage phagocytic capability in rats

BACKGROUND

Ischemic stroke causes brain inflammation, which we postulate may result in lung damage. Several studies have focused on stroke-induced immunosuppression and lung infection; however, the possibility that strokes may trigger lung inflammation has been overlooked. We hypothesized that even focal ischemic stroke might induce acute systemic and pulmonary inflammation, thus altering respiratory parameters, lung tissue integrity, and alveolar macrophage behavior.

METHODS

Forty-eight Wistar rats were randomly assigned to ischemic stroke (Stroke) or sham surgery (Sham). Lung function, histology, and inflammation in the lung, brain, bronchoalveolar lavage fluid (BALF), and circulating plasma were evaluated at 24 h. In vitro, alveolar macrophages from naïve rats (unstimulated) were exposed to serum or BALF from Sham or Stroke animals to elucidate possible mechanisms underlying alterations in alveolar macrophage phagocytic capability. Alveolar macrophages and epithelial and endothelial cells of Sham and Stroke animals were also isolated for evaluation of mRNA expression of interleukin (IL)-6 and tumor necrosis factor (TNF)-α.

RESULTS

Twenty-four hours following ischemic stroke, the tidal volume, expiratory time, and mean inspiratory flow were increased. Compared to Sham animals, the respiratory rate and duty cycle during spontaneous breathing were reduced, but this did not affect lung mechanics during mechanical ventilation. Lungs from Stroke animals showed clear evidence of increased diffuse alveolar damage, pulmonary edema, and inflammation markers. This was associated with an increase in ultrastructural damage, as evidenced by injury to type 2 pneumocytes and endothelial cells, cellular infiltration, and enlarged basement membrane thickness. Protein levels of proinflammatory mediators were documented in the lung, brain, and plasma (TNF-α and IL-6) and in BALF (TNF-α). The phagocytic ability of macrophages was significantly reduced. Unstimulated macrophages isolated from naïve rats only upregulated expression of TNF-α and IL-6 following exposure to serum from Stroke rats. Exposure to BALF from Stroke or Sham animals did not change alveolar macrophage behavior, or gene expression of TNF-α and IL-6. IL-6 expression was increased in macrophages and endothelial cells from Stroke animals.

CONCLUSIONS

In rats, focal ischemic stroke is associated with brain-lung crosstalk, leading to increased pulmonary damage and inflammation, as well as reduced alveolar macrophage phagocytic capability, which seems to be promoted by systemic inflammation.

Radiologic Cerebral Reperfusion at 24 h Predicts Good Clinical Outcome

Cerebral reperfusion and arterial recanalization are radiological features of the effectiveness of thrombolysis in acute ischemic stroke (AIS) patients. Here, an investigation of the prognostic role of early recanalization/reperfusion on clinical outcome was performed. In AIS patients (n = 55), baseline computerized tomography (CT) was performed ≤ 8 h from symptom onset, whereas CT determination of reperfusion/recanalization was assessed at 24 h. Multiple linear and logistic regression models were used to correlate reperfusion/recanalization with radiological (i.e., hemorrhagic transformation, ischemic core, and penumbra volumes) and clinical outcomes (assessed as National Institutes of Health Stroke Scale [NIHSS] reduction ≥ 8 points or a NIHSS ≤ 1 at 24 h and as modified Rankin Scale [mRS] < 2 at 90 days). At 24 h, patients achieving radiological reperfusion were n = 24, while the non-reperfused were n = 31. Among non-reperfused, n = 15 patients were recanalized. Radiological reperfusion vs. recanalization was also confirmed by early increased levels of circulating inflammatory biomarkers (i.e., serum osteopontin). In multivariate analysis, ischemic lesion volume reduction was associated with both recanalization (β = 0.265; p = 0.014) and reperfusion (β = 0.461; p < 0.001), but only reperfusion was independently associated with final infarct volume (β = - 0.333; p = 0.007). Only radiological reperfusion at 24 h predicted good clinical response at day 1 (adjusted OR 16.054 [1.423-181.158]; p = 0.025) and 90-day good functional outcome (adjusted OR 25.801 [1.483-448.840]; p = 0.026). At ROC curve analysis the AUC of reperfusion was 0.777 (p < 0.001) for the good clinical response at 24 h and 0.792 (p < 0.001) for 90-day clinical outcome. Twenty-four-hour radiological reperfusion assessed by CT is associated with good clinical response on day 1 and good functional outcome on day 90 in patients with ischemic stroke.

The Dynamics of Impaired Blood-Brain Barrier Restoration in a Rat Model of Co-morbid Injury

Defect in brain microperfusion is increasingly recognized as an antecedent event to Alzheimer's disease (AD) and ischemia. Nevertheless, studies on the role of impaired microperfusion as a pathological trigger to neuroinflammation, Aβ deposition as well as blood-brain barrier (BBB) disruption, and the etiological link between AD and ischemia are lacking. In this study, we employ in vivo sequential magnetic resonance imaging (MRI) and computed tomography (CT) imaging in a co-morbid rat model of β-amyloid toxicity (Aβ) and ischemia (ET1) with subsequent histopathology of striatal lesion core and penumbra at 1, 7, and 28 days post injury. Within 24 h, cerebral injury resulted in increased BBB permeability due to the dissolution of β-dystroglycan (β-DG) and basement membrane laminin by active matrix metalloproteinase9 (MMP9). As a result, net flow of circulating IgG down a hydrostatic gradient into the parenchyma led to vasogenic edema and impaired perfusion, thus increasing the apparent hyperintensity in true fast imaging with steady-state free precession (true FISP) imaging and acute hypoperfusion in CT. This was followed by a slow recruitment of reactive astroglia to the affected brain and depolarization of aquaporin4 (AQP4) expression resulting in cytotoxic edema-in an attempt to resolve vasogenic edema. On d28, functional BBB was restored in ET1 rats as observed by astrocytic MMP9 release, β-DG stabilization, and new vessel formation. This was confirmed by reduced hyperintensity on true FISP imaging and normalized cerebral blood flow in CT. While, Aβ toxicity alone was not detrimental enough, Aβ+ET1 rats showed delayed differential expression of MMP9, late recruitment of astroglial cells, protracted loss of AQP4 depolarization, and thus delayed BBB restoration and cerebral perfusion.

Acute basilar thrombosis: Recanalization following intravenous thrombolysis is dependent on thrombus length

Introduction

We investigated whether thrombus length measured in Computed Tomography Angiography (CTA) is predictive of the success rate of intravenous thrombolysis (IVT) in acute basilar occlusion and whether recanalization can be achieved by additional mechanical endovascular thrombectomy.

Methods

In 51 patients with acute basilar thrombosis thrombus length was measured on CTA images before intravenous thrombolysis (IVT) with rt-PA was started. After 114 minutes on average success of IVT was evaluated either by CTA or DSA. Patients with persistent basilar occlusion and no major brainstem infarction on CT underwent endovascular recanalization.

Results

87% of patients had no recanalization of basilar artery after IVT alone. The average thrombus length was 15 mm in patients with persistent basilar occlusion after IVT and 7 mm in patients with recanalization after IVT. Thrombi longer than 13 mm did not resolve after IVT alone and 80% of thrombi shorter than 13 mm did not resolve either. 41 patients were transferred to endovascular recanalization; endovascular therapy was performed successfully in 90% (37 / 41).

Conclusions

Recanalization rates in acute basilar occlusion after IVT alone are low and dependent on thrombus length. Additional mechanical endovascular thrombectomy showed to be a very successful recanalization therapy.

Cerebral Ischemic Reperfusion Injury Following Recanalization of Large Vessel Occlusions

Although stroke has recently dropped to become the nation's fifth leading cause of mortality, it remains the top leading cause of morbidity and disability in the US. Recent advances in stroke treatment, including intravenous fibrinolysis and mechanical thromboembolectomy, allow treatment of a greater proportion of stroke patients than ever before. While intra-arterial fibrinolysis with recombinant tissue plasminogen is an effective for treatment of a broad range of acute ischemic strokes, endovascular mechanical thromboembolectomy procedures treat severe strokes due to large artery occlusions, often resistant to intravenous drug. Together, these procedures result in a greater proportion of revascularized stroke patients than ever before, up to 88% in 1 recent trial (EXTEND-IA). Subsequently, there is a growing need for neurointensivists to develop more effective strategies to manage stroke patients following successful reperfusion. Cerebral ischemic reperfusion injury (CIRI) is defined as deterioration of brain tissue suffered from ischemia that concomitantly reverses the benefits of re-establishing cerebral blood flow following mechanical or chemical therapies for acute ischemic stroke. Herein, we examine the pathophysiology of CIRI, imaging modalities, and potential neuroprotective strategies. Additionally, we sought to lay down a potential treatment approach for patients with CIRI following emergent endovascular recanalization for acute ischemic stroke.

MEK/ERK- and calcineurin/NFAT-mediated mechanism of cerebral hyperemia and brain injury following NMDA receptor activation

N-methyl-d-aspartate (NMDA) receptor activation increases regional cerebral blood flow (rCBF) and induces neuronal injury, but similarities between these processes are poorly understood. In this study, by measuring rCBF in vivo, we identified a clear correlation between cerebral hyperemia and brain injury. NMDA receptor activation induced brain injury as a result of rCBF increase, which was attenuated by an inhibitor of mitogen-activated protein kinase or calcineurin. Moreover, NMDA induced phosphorylation of extracellular signal-regulated kinase (ERK) and nuclear translocation of nuclear factor of activated T-cell (NFAT) in neurons. Therefore, a MEK/ERK- and calcineurin/NFAT-mediated mechanism of neurovascular coupling underlies the pathophysiology of neurovascular disorders.

Vectorized nanodelivery systems for ischemic stroke: a concept and a need

Neurological diseases of diverse aetiologies have significant effects on the quality of life of patients. The limited self-repairing capacity of the brain is considered to be the origin of the irreversible and progressive nature of many neurological diseases. Therefore, neuroprotection is an important goal shared by many clinical neurologists and neuroscientists. In this review, we discuss the main obstacles that have prevented the implementation of experimental neuroprotective strategies in humans and propose alternative avenues for the use of neuroprotection as a feasible therapeutic approach. Special attention is devoted to nanotechnology, which is a new approach for developing highly specific and localized biomedical solutions for the study of the multiple mechanisms involved in stroke. Nanotechnology is contributing to personalized neuroprotection by allowing us to identify mechanisms, determine optimal therapeutic windows, and protect patients from brain damage. In summary, multiple aspects of these new players in biomedicine should be considered in future in vivo and in vitro studies with the aim of improving their applicability to clinical studies.

The effects of Y-27632 on pial microvessels during global brain ischemia and reperfusion in rabbits

Background

Global brain ischemia-reperfusion during propofol anesthesia provokes persistent cerebral pial constriction. Constriction is likely mediated by Rho-kinase. Cerebral vasoconstriction possibly exacerbates ischemic brain injury. Because Y-27632 is a potent Rho-kinase inhibitor, it should be necessary to evaluate its effects on cerebral pial vessels during ischemia—reperfusion period. We therefore tested the hypotheses that Y-27632 dilates cerebral pial arterioles after the ischemia-reperfusion injury, and evaluated the time-course of cerebral pial arteriolar status after the ischemia-reperfusion.

Methods

Japanese white rabbits were anesthetized with propofol, and a closed cranial window inserted over the left hemisphere. Global brain ischemia was produced by clamping the brachiocephalic, left common carotid, and left subclavian arteries for 15 min. Rabbits were assigned to cranial window perfusion with: (1) artificial cerebrospinal fluid (Control group, n = 7); (2) topical infusion of Y-27632 10⁻⁶ mol · L⁻¹ for 30 min before the initiation of global brain ischemia (Pre group, n = 7); (3) topical infusion of Y-27632 10⁻⁶ mol · L⁻¹ starting 30 min before ischemia and continuing throughout the study period (Continuous group, n = 7); and, (4) topical infusion of Y-27632 10⁻⁶ mol · L⁻¹ starting 10 min after the ischemia and continuing until the end of the study (Post group, n = 7). Cerebral pial arterial and venule diameters were recorded 30 min before ischemia, just before arterial clamping, 10 min after clamping, and 5, 10, 20, 40, 60, 80, 100, and 120 min after unclamping.

Results

Mean arterial blood pressure and blood glucose concentration increased significantly after global brain ischemia except in the Continuous group. In the Pre and Continuous groups, topical application of Y-27632 produced dilation of large (mean 18–19%) and small (mean; 25–29%) pial arteries, without apparent effect on venules. Compared with the Control and Pre groups, arterioles were significantly dilated during the reperfusion period in the Continuous and Post groups (mean at 120 min: 5–8% in large arterioles and 11–12% in small arterioles).

Conclusions

Y-27632 dilated cerebral pial arterioles during reperfusion. Y-27632 may enhance recovery from ischemia by preventing arteriolar vasoconstriction during reperfusion.

Baseline collateral status and infarct topography in post-ischaemic perilesional hyperperfusion: An arterial spin labelling study

Focal hyperperfusion after acute ischaemic stroke could be of prognostic value depending upon its spatial localisation and temporal dynamics. Factors associated with late stage (12-24 h) perilesional hyperperfusion, identified using arterial spin labelling, are poorly defined. A prospective cohort of acute ischaemic stroke patients presenting within 4.5 h of symptom onset were assessed with multi-modal computed tomography acutely and magnetic resonance imaging at 24 ± 8 h. Multivariate logistic regression analysis and receiver operating characteristics curves were used. One hundred and nineteen hemispheric acute ischaemic stroke patients (mean age = 71 ± 12 years) with 24 h arterial spin labelling imaging were included. Forty-two (35.3%) patients showed perilesional hyperperfusion on arterial spin labelling at 24 h. Several factors were independently associated with perilesional hyperperfusion: good collaterals (71% versus 29%, P < 0.0001; OR = 5, 95% CI = [1.6, 15.7], P = 0.005), major reperfusion (81% versus 48%, P = < 0.0001; OR = 7.5, 95% CI = [1.6, 35.1], P = 0.01), penumbral salvage (76.2% versus 47%, P = 0.002; OR = 6.6, 95% CI = [1.8, 24.5], P = 0.004), infarction in striatocapsular (OR = 9.5, 95% CI = [2.6, 34], P = 0.001) and in cortical superior division middle cerebral artery (OR = 4.7, 95% CI = [1.4, 15.7], P = 0.012) territory. The area under the receiver operating characteristic curve was 0.91. Our results demonstrate good arterial collaterals, major reperfusion, penumbral salvage, and infarct topographies involving cortical superior middle cerebral artery and striatocapsular are associated with perilesional hyperperfusion.

Review of Post Ischemic Stroke Imaging and Its Clinical Relevance

In this day and age, multiple imaging modalities are available to the stroke physician in the post-treatment phase.The practical challenge for physicians who treat stroke is to evaluate the pros and cons of each technique and select the best choice for the situation. The choice of imaging modality remains contentious at best and varies among different institutions and centres. This is no simple task an there are many factors to consider, including the differential diagnosis which need to be evaluated, the availability and reliability of the imaging technique and time and expertise required to perform and interpret the scanning. Other ancillary competing interest also come into play such as the financial cost of the modality, the requirement for patient monitoring during the imaging procedure and patient comfort. In an effort to clear some of the ambiguity surrounding this topic we present some of the current techniques in use and others, which are still in the realm of research and have not yet transitioned into clinical practice.

Mapping the dynamics of brain perfusion using functional ultrasound in a rat model of transient middle cerebral artery occlusion

Following middle cerebral artery occlusion, tissue outcome ranges from normal to infarcted depending on depth and duration of hypoperfusion as well as occurrence and efficiency of reperfusion. However, the precise time course of these changes in relation to tissue and behavioral outcome remains unsettled. To address these issues, a three-dimensional wide field-of-view and real-time quantitative functional imaging technique able to map perfusion in the rodent brain would be desirable. Here, we applied functional ultrasound imaging, a novel approach to map relative cerebral blood volume without contrast agent, in a rat model of brief proximal transient middle cerebral artery occlusion to assess perfusion in penetrating arterioles and venules acutely and over six days thanks to a thinned-skull preparation. Functional ultrasound imaging efficiently mapped the acute changes in relative cerebral blood volume during occlusion and following reperfusion with high spatial resolution (100 µm), notably documenting marked focal decreases during occlusion, and was able to chart the fine dynamics of tissue reperfusion (rate: one frame/5 s) in the individual rat. No behavioral and only mild post-mortem immunofluorescence changes were observed. Our study suggests functional ultrasound is a particularly well-adapted imaging technique to study cerebral perfusion in acute experimental stroke longitudinally from the hyper-acute up to the chronic stage in the same subject.

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.

Disrupted mitochondrial genes and inflammation following stroke

AIMS

Determine the subacute time course of mitochondria disruption, cell death, and inflammation in a rat model of unilateral motor cortical ischemic stroke.

MAIN METHODS

Rats received unilateral ischemia of the motor cortex and were tested on behavioral tasks to determine impairments. Animals were euthanized at 24h, 72h and 144h and mRNA expression of key mitochondria proteins and indicators of inflammation, apoptosis and potential regenerative processes in ipsilesion cortex and striatum, using RT-qPCR. Mitochondrial proteins were examined at 144h using immunoblot analysis.

KEY FINDINGS

Rats with stroke induced-behavioral deficits had sustained, 144h post-lesion, decreases in mitochondrial-encoded electron transport chain proteins NADH dehydrogenase subunit-1 and cytochrome c oxidase subunit-1 (mRNA and protein) and mitochondrial DNA content in perilesion motor and sensory cortex. Uncoupling-protein-2 gene expression, but not superoxide dismutase-2, remained elevated in ipsilateral cortex and striatum at this time. Cortical inflammatory cytokine, interleukin-6, was increased early and was followed by increased macrophage marker F4/80 after stroke. Cleaved caspase-3 activation was elevated in cortex and growth associated protein-43 was elevated in the cortex and striatum six days post-lesion.

SIGNIFICANCE

We identified a relationship between three disrupted pathways, (1) sustained loss of mitochondrial proteins and mitochondrial DNA copy number in the cortex linked to decreased mitochondrial gene transcription; (2) early inflammatory response mediated by interleukin- 6 followed by macrophages; (3) apoptosis in conjunction with the activation of regenerative pathways. The stroke-induced spatial and temporal profiles lay the foundation to target pharmacological therapeutics to these three pathways.

Post-ischaemic hyperperfusion in traumatic middle cerebral artery dissection detected by arterial spin labelling of magnetic resonance imaging

We report a patient with a traumatic middle cerebral artery dissection, which showed hyperperfusion in the territory supplied by the left middle cerebral artery. A 45-year-old man experienced speech disturbance and motor weakness in his right hemibody on the day following mild head trauma. His symptoms worsened on the fourth day. Magnetic resonance imaging showed narrowing in the left M1 portion of the middle cerebral artery. Angiography showed narrowing and dilatation in the left middle cerebral artery trunk. The lesion was diagnosed as a dissection of the middle cerebral artery. Arterial spin labelling of magnetic resonance imaging and single photon emission computed tomography showed increased cerebral blood flow in the left temporal region compared with the right. The patient was treated conservatively and the symptoms gradually improved. The hyperperfusion observed on arterial spin labelling and single photon emission computed tomography gradually improved and disappeared on the 25th day. This is the first reported case of traumatic middle cerebral artery dissection, which showed post-ischaemic hyperperfusion in the territory of the affected artery. To detect hyperperfusion in the brain, arterial spin labelling is a useful technique.

Neurocritical Care of Emergent Large-Vessel Occlusion: The Era of a New Standard of Care

Acute ischemic stroke continues to be one of the leading causes of morbidity and mortality worldwide. Recent advances in mechanical thrombectomy techniques combined with prereperfusion computed tomographic angiography for patient selection have revolutionized stroke care in the past year. Peri- and postinterventional neurocritical care of the patient who has had an emergent large-vessel occlusion is likely an equally important contributor to the outcome but has been relatively neglected. Critical periprocedural management issues include streamlining care to speed intervention, blood pressure optimization, reversal of anticoagulation, management of agitation, and selection of anesthetic technique (ie, general vs monitored anesthesia care). Postprocedural critical care issues that might modulate neurological outcome include blood pressure and glucose optimization, avoidance of fever or hyperoxia, fluid and nutritional management, and early integration of rehabilitation into the intensive care unit setting. In this review, we sought to lay down an evidence-based strategy for patients with acute ischemic stroke undergoing emergent endovascular reperfusion.

Tissue-Negative Transient Ischemic Attack: Is There a Role for Perfusion MRI?

OBJECTIVE

Approximately 60% of patients with a clinical transient ischemic attack (TIA) do not have DWI evidence of cerebral ischemia. The purpose of this study was to assess the added diagnostic value of perfusion MRI in the evaluation of patients with TIA who have normal DWI findings.

MATERIALS AND METHODS

The inclusion criteria for this retrospective study were clinical presentation of TIA at admission with a discharge diagnosis of TIA confirmed by a stroke neurologist, MRI including both DWI and perfusion-weighted imaging within 48 hours of symptom onset, and no DWI lesion. Cerebral blood flow (CBF) and time to maximum of the residue function (Tmax) maps were evaluated independently by two observers. Multivariate analysis was used to assess perfusion findings; clinical variables; age, blood pressure, clinical symptoms, diabetes (ABCD2) score; duration of TIA; and time between MRI and onset and resolution of symptoms.

RESULTS

Fifty-two patients (33 women, 19 men; age range, 20-95 years) met the inclusion criteria. A regional perfusion abnormality was identified on either Tmax or CBF maps of 12 of 52 (23%) patients. Seven (58%) of the patients with perfusion abnormalities had hypoperfused lesions best detected on Tmax maps; the other five had hyperperfusion best detected on CBF maps. In 11 of 12 (92%) patients with abnormal perfusion MRI findings, the regional perfusion deficit correlated with the initial neurologic deficits. Multivariable analysis revealed no significant difference in demographics, ABCD2 scores, or presentation characteristics between patients with and those without perfusion abnormalities.

CONCLUSION

Perfusion MRI that includes Tmax and CBF parametric maps adds diagnostic value by depicting regions with delayed perfusion or postischemic hyperperfusion in approximately one-fourth of TIA patients who have normal DWI findings.

Single photon emission computed tomography imaging of cerebral blood flow, blood–brain barrier disruption, and apoptosis time course after focal cerebral ischemia in rats

Background

Cerebral ischemia is a leading cause of disability worldwide and no other effective therapy has been validated to date than intravenous thrombolysis. In this context, many preclinical models have been developed and recent advances in preclinical imaging represent promising tools. Thus, we proposed here to characterize in vivo time profiles of cerebral blood flow, blood–brain barrier disruption and apoptosis following a transient middle cerebral artery occlusion in rats using SPECT/CT imaging.

Methods

Rats underwent a 1-h middle cerebral artery occlusion followed by reperfusion. Cerebral blood flow, blood–brain barrier disruption and apoptosis were evaluated by SPECT/CT imaging using respectively 99mTc-HMPAO, 99mTc-DTPA and the experimental 99mTc-Annexin V-128, up to 14 days after middle cerebral artery occlusion. Histological evaluation of apoptosis has been performed using TUNEL method to validate the 99mTc-Annexin V-128 uptake.

Results

99mTc-HMPAO cerebral blood flow evaluation showed hypoperfusion during occlusion, partially restored on days 4 and 7 and sustained up to 14 days after middle cerebral artery occlusion. 99mTc-DTPA SPECT/CT showed a blood–brain barrier disruption starting on day 1 post-middle cerebral artery occlusion, peaking on day 2, with barrier integrity totally restored on day 7. 99mTc-Annexin V-128 SPECT/CT imaging showed significant positive correlation with TUNEL immunohistochemistry and allowed ischemic-induced apoptosis to be detected from day 2 to day 7, peaking on day 3 after middle cerebral artery occlusion.

Conclusions

Using SPECT/CT imaging, we showed that after transient middle cerebral artery occlusion in rat there was a sustained decrease in cerebral blood flow followed by blood–brain barrier disruption preceding meanwhile apoptosis. Rodent SPECT/CT imaging of cerebral blood flow, blood–brain barrier disruption and apoptosis appears to be an efficient tool for evaluating neuroprotective drugs and regenerative therapies against cerebral ischemia and time-windows for therapeutic intervention.

Brain tissue oxygen evaluation by wireless near-infrared spectroscopy

BACKGROUND

Monitoring the partial pressure of oxygen in brain tissue (PbtO2) is an important tool for traumatic brain injury (TBI) but is invasive and inconvenient for real time monitoring. Near-infrared spectroscopy (NIRS), which can monitor hemoglobin parameters in the brain tissue, has been used widely as a noninvasive tool for assessing cerebral ischemia and hypoxia. Therefore, it may have the potential as a noninvasive tool for estimating the change of PbtO2. In this study, a novel wireless NIRS system was designed to monitor hemoglobin parameters of rat brains under different impact strengths and was used to estimate the change of PbtO2 noninvasively in TBI.

MATERIALS AND METHODS

The proposed wireless NIRS system and a PbtO2 monitoring system were used to monitor the oxygenation of rat brains under different impact strengths. Rats were randomly assigned to four different impact strength groups (sham, 1.6 atm, 2.0 atm, and 2.4 atm; n = 6 per group), and the relationships of concentration changes in oxyhemoglobin (HbO2), deoxyhemoglobin (HbR), and total hemoglobin (HbT), and PbtO2 during and after TBI with different impact strengths were investigated. Triphenyltetrazolium chloride (TTC) staining was also used to evaluate infarction volume.

RESULTS

Concentration changes in HbO2, HbR, and HbT dropped immediately after the impact, increased gradually, and then became stable. Changes in PbtO2 had a similar tendency with the hemoglobin parameters. There was significant correlation between changes in PbtO2 and HbO2 (correlation = 0.76) but not with changes in HbR (correlation = 0.06). In triphenyltetrazolium chloride staining, the infarction volume was highly but negatively associated with oxygen-related parameters like PbtO2 and HbO2.

CONCLUSIONS

Changes in HbO2 under TBI was highly and positively correlated with changes in PbtO2. By using the relative changes in HbO2 as a reference parameter, the proposed wireless NIRS system may be developed as a noninvasive tool for estimating the change of PbtO2 in brain tissue after TBI.

The influence of decompressive craniectomy for major stroke on early cerebral perfusion

OBJECT

Multiple trials have shown improved survival and functional outcome in patients treated with decompressive craniectomy (DC) for brain swelling following major stroke. It has been assumed that decompression induces an improvement in cerebral perfusion. This observational study directly measured cerebral perfusion before and after decompression.

METHODS

Sixteen patients were prospectively examined with perfusion CT within 6 hours prior to surgery and 12 hours after surgery. Preoperative and postoperative perfusion measurements were compared and correlated.

RESULTS

Following DC there was a significant increase in cerebral blood flow in all measured territories and additionally an increase in cerebral blood volume in the penumbra (p = 0.03). These changes spread as far as the contralateral hemisphere. No significant changes in mean transit time or Tmax (time-to-peak residue function) were observed.

CONCLUSIONS

The presurgical perfusion abnormalities likely reflected local pressure-induced hypoperfusion with impaired autoregulation. The improvement in perfusion after decompression implied an increase in perfusion pressure, likely linked to partial restoration of autoregulation. The increase in perfusion that was observed might partially be responsible for improved clinical outcome following decompressive surgery for major stroke. The predictive value of perfusion CT on outcome needs to be evaluated in larger trials.

State-of-the-art MRI techniques in neuroradiology: principles, pitfalls, and clinical applications

This article reviews the most relevant state-of-the-art magnetic resonance (MR) techniques, which are clinically available to investigate brain diseases. MR acquisition techniques addressed include notably diffusion imaging (diffusion-weighted imaging (DWI), diffusion tensor imaging (DTI), and diffusion kurtosis imaging (DKI)) as well as perfusion imaging (dynamic susceptibility contrast (DSC), arterial spin labeling (ASL), and dynamic contrast enhanced (DCE)). The underlying models used to process these images are described, as well as the theoretic underpinnings of quantitative diffusion and perfusion MR imaging-based methods. The technical requirements and how they may help to understand, classify, or follow-up neurological pathologies are briefly summarized. Techniques, principles, advantages but also intrinsic limitations, typical artifacts, and alternative solutions developed to overcome them are discussed. In this article, we also review routinely available three-dimensional (3D) techniques in neuro MRI, including state-of-the-art and emerging angiography sequences, and briefly introduce more recently proposed 3D quantitative neuro-anatomy sequences, and new technology, such as multi-slice and multi-transmit imaging.

Postischemic hyperperfusion on arterial spin labeled perfusion MRI is linked to hemorrhagic transformation in stroke

The purpose of this study was to investigate the relationship between hyperperfusion and hemorrhagic transformation (HT) in acute ischemic stroke (AIS). Pseudo-continuous arterial spin labeling (ASL) with background suppressed 3D GRASE was performed during routine clinical magnetic resonance imaging (MRI) on AIS patients at various time points. Arterial spin labeling cerebral blood flow (CBF) maps were visually inspected for the presence of hyperperfusion. Hemorrhagic transformation was followed during hospitalization and was graded on gradient recalled echo (GRE) scans into hemorrhagic infarction (HI) and parenchymal hematoma (PH). A total of 361 ASL scans were collected from 221 consecutive patients with middle cerebral artery stroke from May 2010 to September 2013. Hyperperfusion was more frequently detected posttreatment (odds ratio (OR) = 4.8, 95% confidence interval (CI) 2.5 to 8.9, P < 0.001) and with high National Institutes of Health Stroke Scale (NIHSS) scores at admission (P<0.001). There was a significant association between having hyperperfusion at any time point and HT (OR = 3.5, 95% CI 2.0 to 6.3, P < 0.001). There was a positive relationship between the grade of HT and time-hyperperfusion with the Spearman's rank correlation of 0.44 (P = 0.003). Arterial spin labeling hyperperfusion may provide an imaging marker of HT, which may guide the management of AIS patients post tissue-type plasminogen activator (tPA) and/or endovascular treatments. Late hyperperfusion should be given more attention to prevent high-grade HT.

Multimodal imaging in acute ischemic stroke

OPINION STATEMENT

Recent years have seen the development of novel neuroimaging techniques whose roles in the management of acute stroke are sometimes confusing and controversial. This may be attributable in part to a focus on establishing simplified algorithms and terminology that omit consideration of the basic pathophysiology of cerebral ischemia and, consequently, of the full potential for optimizing patients' care based upon their individual imaging findings. This review begins by discussing cerebral hemodynamic physiology and of the effects of hemodynamic disturbances upon the brain. Particular attention will be paid to the hemodynamic measurements and markers of tissue injury that are provided by common clinical imaging techniques, with the goal of enabling greater confidence and flexibility in understanding the potential uses of these techniques in various clinical roles, which will be discussed in the remainder of the review.

Multi-modal CT scanning in the evaluation of cerebrovascular disease patients

Ischemic stroke currently represents one of the leading causes of severe disability and mortality in the Western World. Until now, angiography was the most used imaging technique for the detection of the extra-cranial and intracranial vessel pathology. Currently, however, non-invasive imaging tool like ultrasound (US), magnetic resonance (MR) and computed tomography (CT) have proven capable of offering a detailed analysis of the vascular system. CT in particular represents an advanced system to explore the pathology of carotid arteries and intracranial vessels and also offers tools like CT perfusion (CTP) that provides valuable information of the brain's vascular physiology by increasing the stroke diagnostic. In this review, our purpose is to discuss stroke risk prediction and detection using CT.