Characterization of gadolinium-based dynamic susceptibility contrast perfusion measurements in permanent and transient MCAO models with volumetric based validation by CASL.
ABSTRACT: Perfusion imaging is crucial in imaging of ischemic stroke to determine 'tissue at risk' for infarction. In this study we compared the volumetric quantification of the perfusion deficit in two rat middle-cerebral-artery occlusion (MCAO) models using two gadolinium-based contrast agents (P1152 (Guerbet) and Magnevist (Bayer-Schering, Pittsburgh, PA, USA)) as compared with our well established continuous arterial spin labeling (CASL) perfusion imaging technique. Animals underwent either permanent MCAO or transient MCAO with 80-min reperfusion. Imaging was performed at four different time points after MCAO. A region-of-interest (ROI) analysis of the subregions of the ischemic zone (core, penumbra, transient reversal (TR), and sustained reversal (SR)) using P1152 showed significant reduction in blood flow in the core and TR subregions relative to the penumbral and SR subregions while occluded. After reperfusion, a significant increase in blood flow was recorded at all time points after reperfusion in all regions except TR. From the ROI analysis the threshold for the penumbra was determined to be -62+/-11% and this value was subsequently used for quantification of the volumetric deficit. The ischemic volume as defined by dynamic susceptibility contrast (DSC), was only statistically different from the CASL-derived ischemic volume when using Magnevist at post-reperfusion time points.
Project description:Reperfusion exceeded time window may induce ischemia/reperfusion injury, increase hemorrhagic transformation, and deteriorate neurological outcomes in ischemic stroke models. However, the increasing clinical evidences supported that reperfusion even within 6-24?h may salvage ischemic tissue and improve neurological outcomes in selected large vessel occlusion patients, without inducing serious ischemia/reperfusion injury and hemorrhagic transformation. The underlying molecular mechanisms are less clear. In present study, we demonstrated that delayed recanalization at 3?days after permanent middle cerebral artery occlusion (MCAO) decreased infarct volumes and improved neurobehavioral deficits in rats, with no increasing animal mortality and intracerebral hemorrhage. Meanwhile, we observed that endogenous neuroprotective agent fibroblast growth factor 21 (FGF21) significantly increased in serum after MCAO, but which did not synchronously increase in penumbra due to permanent MCAO. Recanalization dramatically increased the endogenous FGF21 expression on neurons in penumbra after MCAO. We confirmed that FGF21 activated the FGFR1/PI3K/Caspase-3 signaling pathway, which attenuated neuronal apoptosis in penumbra. Conversely, knockdown of FGFR1 via FGFR1 siRNA abolished the anti-apoptotic effects of FGF21, and in part abrogated beneficial effects of recanalization on neurological outcomes. These findings suggested that delayed recanalization at 3?days after MCAO improved neurological outcomes in rats via increasing endogenous FGF21 expression and activating FGFR1/PI3K/Caspase-3 pathway to attenuate neuronal apoptosis in penumbra. Delayed recanalization at 3?days after ischemic stroke onset may be a promising treatment strategy in selected patients.
Project description:<b>Background</b>: Following ischemic stroke, recanalisation and restoration of blood flow to the affected area of the brain is critical and directly correlates with patient recovery. <i>In vivo</i> models of ischemic stroke show high variability in outcomes, which may be due to variability in reperfusion. We previously reported that a surgical refinement in the middle cerebral artery occlusion (MCAO) model of stroke, via repair of the common carotid artery (CCA), removes the reliance on the Circle of Willis for reperfusion and reduced infarct variability. Here we further assess this refined surgical approach on reperfusion characteristics following transient MCAO in mice. <b>Methods</b>: Mice underwent 60 min of MCAO, followed by either CCA repair or ligation at reperfusion. All mice underwent laser speckle contrast imaging at baseline, 24 h and 48 h post-MCAO. <b>Results</b>: CCA ligation reduced cerebral perfusion in the ipsilateral hemisphere compared to baseline (102.3 ± 4.57%) at 24 h (85.13 ± 16.09%; P < 0.01) and 48 h (75.04 ± 12.954%; P < 0.001) post-MCAO. Repair of the CCA returned perfusion to baseline (94.152 ± 2.44%) levels and perfusion was significantly improved compared to CCA ligation at both 24 h (102.83 ± 8.41%; P < 0.05) and 48 h (102.13 ± 9.34%; P < 0.001) post-MCAO. <b>Conclusions</b>: Our findings show CCA repair, an alternative surgical approach for MCAO, results in improved ischemic hemisphere perfusion during the acute phase.
Project description:Whole brain computed tomography perfusion (CTP) has the potential to select eligible patients for reperfusion therapy. We aimed to find the optimal thresholds on baseline CTP for ischemic core and penumbra in acute ischemic stroke. We reviewed patients with acute ischemic stroke in the anterior circulation, who underwent baseline whole brain CTP, followed by intravenous thrombolysis and perfusion imaging at 24 hours. Patients were divided into those with major reperfusion (to define the ischemic core) and minimal reperfusion (to define the extent of penumbra). Receiver operating characteristic (ROC) analysis and volumetric consistency analysis were performed separately to determine the optimal threshold by Youden's Index and mean magnitude of volume difference, respectively. From a series of 103 patients, 22 patients with minimal-reperfusion and 47 with major reperfusion were included. Analysis revealed delay time ? 3 s most accurately defined penumbra (AUC = 0.813; 95% CI, 0.812-0.814, mean magnitude of volume difference = 29.1 ml). The optimal threshold for ischemic core was rCBF ? 30% within delay time ? 3 s (AUC = 0.758; 95% CI, 0.757-0.760, mean magnitude of volume difference = 10.8 ml). In conclusion, delay time ? 3 s and rCBF ? 30% within delay time ? 3 s are the optimal thresholds for penumbra and core, respectively. These results may allow the application of the mismatch on CTP to reperfusion therapy.
Project description:<h4>Aims</h4>To precisely characterize the penumbra by MRI based on a modified photothrombotic stroke mouse model.<h4>Methods</h4>The proximal middle cerebral artery was occluded by a convenient laser system in conjunction with an intravenous injection of Rose Bengal in mice. And the suture MCAO model was performed in seven mice as a comparison of the reproducibility. One hour after occlusion, the penumbra was defined in six random photothrombotic stroke mice by mismatch between perfusion-weighted imaging and the apparent diffusion coefficient map on a home-made workstation. After imaging, three random mice of them were chosen to perform the reperfusion surgery. And the other three mice were sacrificed to stain for several potential penumbra markers, such as c-fos and heart shock protein 90. In the remaining mice, the evolution of the lesions was detected on the apparent diffusion coefficient map, diffusion-weighted imaging and T2-weighted imaging at 1, 3, 6, 12 and 24 hours. After evaluating the neurological deficit scores, the brains were sectioned and stained by triphenyltetrazolium chloride and Nissl.<h4>Results</h4>The mice subjected to photothrombosis showed significant behavioral deficits. One hour after occlusion, the low perfusion areas on the perfusion-weighted imaging interlaced with the hypointense areas on the apparent diffusion coefficient map, demonstrating that the penumbra was located both surrounding and inside the lesions. This phenomenon was subsequently confirmed by the c-fos and heart shock protein 90 staining. The final T2-weighted images of the mice subjected to the reperfusion surgery were also consistent with the penumbra images at one hour. At early stages, the lesions were clearly identified on the apparent diffusion coefficient map; the volumes of the lesions on the diffusion-weighted imaging and T2-weighted imaging did not reach a maximum until 12 hours. The coefficient of variation (CV) of the final lesions in the photothrombotic stroke mice was 21.7% (0.08 of 0.37) on T2-weighted imaging and 27.8% (0.10 of 0.35) on triphenyltetrazolium chloride, representing a high reproducibility (n = 7). While the CV of the lesions in the MCAO stroke mice was only 70% (0.24 of 0.34, n = 4).<h4>Conclusions</h4>This study has provided a precise imaging definition of the penumbra based on a reproducible photothrombotic stroke mouse model.
Project description:AIMS:To validate whether the optimal magnetic resonance perfusion (MRP) thresholds for ischemic penumbra and infarct core, between voxel and volume-based analysis, are varied greatly among Chinese acute ischemic stroke patients. MATERIALS AND METHODS:Acute ischemic stroke patients receiving intravenous thrombolysis within 6 h of onset that obtained acute and 24-h MRP were reviewed. Patients with either no reperfusion (<30% reperfusion at 24 h) or successful reperfusion (>70% reperfusion at 24 h) were enrolled to investigate the ischemic penumbra and infarct core, respectively. The final infarct was assessed on 24-h diffusion-weighted imaging (DWI), which was retrospectively matched to the baseline perfusion-weighted imaging (PWI) images by volume or voxel-based analysis. The optimal thresholds that determined by each approach were compared. RESULTS:From June 2009 to Jan 2014, of 50 patients enrolled, 19 patients achieved no reperfusion, and 20 patients reperfused at 24 h. In patients with no reperfusion, Tmax > 6 seconds was proved of the best agreement with the final infarct in both volumetric analysis (ratio: 1.05, 95% limits of agreement:-0.23 to 2.33, P < 0.001) and voxel-by-voxel analysis (sensitivity: 72.3%, specificity: 74.3%). In patients with reperfusion, rMTT>225% (ratio:2.4, 95% limits of agreement: -6.5 to 11.4, P < 0.001) was found of the best volumetric agreement with the final infarct, while Tmax > 5.6 seconds (sensitivity: 76.8%, specificity: 70.3%) performed most accurately in voxel-based analysis. CONCLUSION:Among Chinese acute stroke patients, volume of Tmax >6 seconds may precisely target ischemic penumbra tissue as good as voxel-based analysis performed, albeit no concordant MRP parameter is found to accurately predict infarct core because reperfusion occurred within 24 h after thrombolysis fails to restrain the infarct growth.
Project description:The penumbra is sustained by an increased extraction of oxygen (OEF) from blood to brain tissue. Metabolic imaging may improve penumbra specificity when examining stroke patients with wake-up stroke and a long time between admission and symptom onset. We used MRI to examine OEF, and compared the volume of regions with elevated OEF to the volume of regions with perfusion deficit in a M2 occlusion model (M2CAO) with preserved collateral blood flow. OEF was calculated from BOLD MRI examining tissue R2', with ASL perfusion imaging employed to determine cerebral blood flows (CBF) and volumes. Diffusion imaging was used to identify the ischemic core (IC). Examinations were performed during and after transient M2CAO in rats. The IC-OEF mismatch was significantly smaller than the IC-CBF mismatch during M2CAO. The penumbra OEF was significantly increased during M2CAO, and decreased significantly after reperfusion. The IC-OEF mismatch may provide increased penumbra specificity compared to IC-CBF mismatch regimens. Results strongly indicate the potential of metabolic MRI for thrombectomy patient selection in cases with a long time from symptom onset to admission. Results demonstrate the effectiveness of reperfusion in alleviating metabolic disturbances in ischemic regions, emphasizing fast treatment to achieve significant neurological recovery in stroke patients.
Project description:Accurate imaging of ischemic penumbra is crucial for improving the management of acute stroke patients. T2* magnetic resonance imaging (MRI) combined with a T2*oxygen challenge (T2*OC) is being developed to detect penumbra based on changes in blood deoxyhemoglobin. Using 100% O2, T2*OC-defined penumbra exhibits ongoing glucose metabolism and tissue recovery on reperfusion. However, potential limitations in translating this technique include a sinus artefact in human scans with delivery of 100% OC and relatively small signal changes. Here we investigate whether an oxygen-carrying perfluorocarbon (PFC) emulsion can enhance the sensitivity of the technique, enabling penumbra detection with lower levels of inspired oxygen. Stroke was induced in male Sprague-Dawley rats (n=17) with ischemic injury and perfusion deficit determined by diffusion and perfusion MRI, respectively. T2* signal change was measured in regions of interest (ROIs) located within ischemic core, T2*OC-defined penumbra and equivalent contralateral areas during 40% O2±prior PFC injection. Region of interest analyses between groups showed that PFC significantly enhanced the T2* response to 40% O2 in T2*-defined penumbra (mean increase of 10.6±2.3% compared to 5.6±1.5% with 40% O2, P<0.001). This enhancement was specific to the penumbra ROI. Perfluorocarbon emulsions therefore enhances the translational potential of the T2*OC technique for identifying penumbra in acute stroke patients.
Project description:Accurate identification of ischemic penumbra will improve stroke patient selection for reperfusion therapies and clinical trials. Current magnetic resonance imaging (MRI) techniques have limitations and lack validation. Oxygen challenge T(2)(*) MRI (T(2)(*) OC) uses oxygen as a biotracer to detect tissue metabolism, with penumbra displaying the greatest T(2)(*) signal change during OC. [(14)C]2-deoxyglucose (2-DG) autoradiography was combined with T(2)(*) OC to determine metabolic status of T(2)(*)-defined penumbra. Permanent middle cerebral artery occlusion was induced in anesthetized male Sprague-Dawley rats (n=6). Ischemic injury and perfusion deficit were determined by diffusion- and perfusion-weighted imaging, respectively. At 147 ± 32 minutes after stroke, T(2)(*) signal change was measured during a 5-minute 100% OC, immediately followed by 125 μCi/kg 2-DG, intravenously. Magnetic resonance images were coregistered with the corresponding autoradiograms. Regions of interest were located within ischemic core, T(2)(*)-defined penumbra, equivalent contralateral structures, and a region of hyperglycolysis. A T(2)(*) signal increase of 9.22% ± 3.9% (mean ± s.d.) was recorded in presumed penumbra, which displayed local cerebral glucose utilization values equivalent to contralateral cortex. T(2)(*) signal change was negligible in ischemic core, 3.2% ± 0.78% in contralateral regions, and 1.41% ± 0.62% in hyperglycolytic tissue, located outside OC-defined penumbra and within the diffusion abnormality. The results support the utility of OC-MRI to detect viable penumbral tissue following stroke.
Project description:Cerebral blood flow and oxygenation in the first few hours after reperfusion following ischemic stroke are critical for therapeutic interventions but are not well understood. We investigate changes in oxyhemoglobin (HbO2) concentration in the cortex during and after ischemic stroke, using multispectral optical imaging in anesthetized mice, a remote filament to induce either 30 minute middle cerebral artery occlusion (MCAo), sham surgery or anesthesia alone. Immunohistochemistry establishes cortical injury and correlates the severity of damage with the change of oxygen perfusion. All groups were imaged for 6 hours after MCAo or sham surgery. Oxygenation maps were calculated using a pathlength scaling algorithm. The MCAo group shows a significant drop in HbO2 during occlusion and an initial increase after reperfusion. Over the subsequent 6 hours HbO2 concentrations decline to levels below those observed during stroke. Platelets, activated microglia, interleukin-1?, evidence of BBB breakdown and neuronal stress increase within the stroked hemisphere and correlate with the severity of the delayed reperfusion deficit but not with the ?HbO2 during stroke. Despite initial restoration of HbO2 after 30 min MCAo there is a delayed compromise that coincides with inflammation and could be a target for improved stroke outcome after thrombolysis.
Project description:Previous studies have shown that the pial microcirculation remodeling improves neurological outcome after middle cerebral artery occlusion (MCAO), accompanied by higher expression of vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS), modulating in vivo angiogenesis. This study was aimed to assess the effects of bone marrow mesenchymal stem cells (BM-MSCs) infused after MCAO on rat pial microcirculation. Animals were subjected to 2 h MCAO followed by BM-MSCs infusion into internal carotid artery. Pial microcirculation was observed at different reperfusion times by fluorescence microscopy. Geometric characteristics of arteriolar networks, permeability increase, leukocyte adhesion, perfused capillary density, VEGF, and endothelial nitric oxide synthase (e-NOS) expression were evaluated. Green fluorescent protein (GFP)-BM-MSCs were used to evaluate their distribution and cell phenotype development during reperfusion. BM-MSCs stimulated a geometric rearrangement of pial networks with formation of new anastomotic vessels sprouting from preexistent arterioles in the penumbra at 7-14-28 days of reperfusion. At the same time VEGF and eNOS expression increased. GFP-BM-MSCs appear to be involved in endothelial and smooth muscle cell programming in the infarcted area. In conclusion, transient MCAO induced pial vascular remodeling characterized by arteriolar anastomotic arcades (originated from preexistent arterioles in penumbra area) able to overlap the ischemic core supplying blood to the neuronal tissue. BM-MSCs appear to accelerate angiogenic processes facilitating new vessel formation; this mechanism was promoted by an increase in VEGF and eNOS expression.