Neuroprotective effect of hyperbaric oxygen therapy monitored by MR-imaging after embolic stroke in rats

The potential neuroprotective effects of hyperbaric oxygen (HBO) were tested in an embolic model of focal cerebral ischemia with partially spontaneous reperfusion. Rats (n = 10) were subjected to embolic middle cerebral artery occlusion (MCAO) and diffusion weighted MRI (DWI) was performed at baseline, 1, 3, and 6 h after MCAO to determine the ADC viability threshold yielding the lesion volumes that best approximated the 2,3,5-triphenyltetrazolium chloride (TTC) infarct volumes at 24 h (experiment 1). For assessment of neuroprotective effects, rats were treated with 100% oxygen at 2.5 atmospheres absolute (ATA, n = 15) or normobaric room air (n = 15) for 60 min beginning 180 min after MCAO (experiment 2). DWI-, perfusion (PWI)- and T2-weighted MRI (T2WI) started within 0.5 h after MCAO and was continued 5 h, 24 h (PWI and T2WI only), and 168 h (T2WI only). Infarct volume was calculated based on TTC-staining at 24 h (experiment 1) or 168 h (experiment 2) post-MCAO. ADC-lesion evolution was maximal between 3 and 6 h. In experiment 2, the relative regional cerebral blood volume (rCBV) of both groups showed similar incomplete spontaneous reperfusion in the ischemic core. HBO reduced infarct volume to 145.3 +/- 39.6 mm3 vs. 202.5 +/- 58.3 mm3 (control, P = 0.029). As shown by MRI and TTC, HBO treatment demonstrated significant neuroprotection at 5 h after embolic focal cerebral ischemia that lasted for 168 h.     

Dynamic susceptibility contrast-enhanced perfusion MR imaging at 1.5 T predicts final infarct size in a rat stroke model

The purpose of the present animal experiment was to determine whether source images from dynamic susceptibility contrast-enhanced perfusion weighted imaging (DSC-PWI) at a 1.5T MR scanner, performed early after photochemically induced thrombosis (PIT) of cerebral middle artery (MCA), is feasible to predict final cerebral infarct size in a rat stroke model. Fifteen rats were subjected to PIT of proximal MCA. T2 weighted imaging (T2WI), diffusion-weighted imaging (DWI), and contrast-enhanced PWI were obtained at 1 h and 24 h after MCA occlusion. The relative lesion size (RLS) was defined as lesion volume/brain volume x 100% and measured for MR images, and compared with the final RLS on the gold standard triphenyl tetrazolium chloride (TTC) staining at 24 h. One hour after MCA occlusion, the RLS with DSC-PWI was 24.9 +/- 6.3%, which was significantly larger than 17.6 +/- 4.8% with DWI (P < 0.01). At 24 h, the final RLS on TTC was 24.3 +/- 4.8%, which was comparable to 25.1 +/- 3.5%, 24.6 +/- 3.6% and 27.9 +/- 6.8% with T2WI, DWI and DSC-PWI respectively (P > 0.05). The fact that at 1 h after MCA occlusion only the displayed perfusion deficit was similar to the final infarct size on TTC (P > 0.05) suggests that early source images from DSC-PWI at 1.5T MR scanner is feasible to noninvasively predict the final infarct size in rat models of stroke.     

Transient and permanent resolution of ischemic lesions on diffusion-weighted imaging after brief periods of focal ischemia in rats : correlation with histopathology

BACKGROUND AND PURPOSE: The early ischemic lesions demonstrated by diffusion-weighted imaging (DWI) are potentially reversible. The purposes of this study were to determine whether resolution of initial DWI lesions is transient or permanent after different brief periods of focal brain ischemia and to evaluate histological outcomes. METHODS: Sixteen rats were subjected to 10 minutes (n=7) or 30 minutes (n=7) of temporary middle cerebral artery occlusion or sham operation (n=2). DWI, perfusion-weighted imaging (PWI), and T(2)-weighted imaging (T(2)WI) were performed during occlusion; immediately after reperfusion; and at 0.5, 1.0, 1.5, 12, 24, 48, and 72 hours after reperfusion. After the last MRI study, the brains were fixed, sectioned, stained with hematoxylin and eosin, and evaluated for neuronal necrosis. RESULTS: No MRI or histological abnormalities were observed in the sham-operated rats. In both the 10-minute and 30-minute groups, the perfusion deficits and DWI hyperintensities that occurred during occlusion disappeared shortly after reperfusion. The DWI, PWI, and T(2)WI results remained normal thereafter in the 10-minute group, whereas secondary DWI hyperintensity and T(2)WI abnormalities developed at the 12-hour observation point in the 30-minute group. Histological examinations demonstrated neuronal necrosis in both groups, but the number of necrotic neurons was significantly higher in the 30-minute group (95+/-4%) than in the 10-minute group (17+/-10%, P<0.0001). CONCLUSIONS: Transient or permanent resolution of initial DWI lesions depends on the duration of ischemia. Transient resolution of DWI lesions is associated with widespread neuronal necrosis; moreover, permanent resolution of DWI lesions does not necessarily indicate complete salvage of brain tissue from ischemic injury.     

Reversible focal ischemic injury demonstrated by diffusion-weighted magnetic resonance imaging in rats.

BACKGROUND AND PURPOSE: Diffusion-weighted magnetic resonance imaging (DWI) can quantitatively display focal brain abnormalities within minutes after the onset of ischemia. We performed the present study to determine the effects of 1 and 2 hours of temporary ischemia on DWI. METHODS: We examined DWI and T2-weighted magnetic resonance images (T2WI) during and after 1 and 2 hours of temporary middle cerebral artery occlusion in rats (n = 10 for each group). In a subgroup of four animals from each group, we employed perfusion magnetic resonance imaging to monitor cerebral perfusion. Neurological outcome and infarct size after survival for 24 hours were compared between the groups and correlated with DWI and T2WI studies. RESULTS: Perfusion studies qualitatively documented hypoperfusion and reperfusion during and after temporary occlusion. Lesion size on DWI during reperfusion was significantly less than that during ischemia for 1 (55% decline, p less than 0.02) but not 2 hours of occlusion. The DWI signal intensity ratio (intensity compared with that in the contralateral homologous area) just before withdrawal of the occluder was significantly less in regions where the hyperintensity disappeared after withdrawal than in regions with persistent hyperintensity (p less than 0.002). The T2WI studies revealed few or no abnormalities, except after 2 hours of occlusion. The neurological outcome was significantly better in the 1-hour than in the 2-hour group (p less than 0.05). Postmortem infarct volume was significantly smaller in the 1-hour group than in the 2-hour group (p less than 0.05). The postwithdrawal DWI accurately predicted infarct size (R = 0.96, p less than 0.0001). CONCLUSIONS: The present study indicates that DWI can rapidly display not only irreversible but also reversible ischemic brain damage and enhances the importance of DWI as a diagnostic modality for stroke.     

Normobaric hyperoxia delays perfusion/diffusion mismatch evolution, reduces infarct volume, and differentially affects neuronal cell death pathways after suture middle cerebral artery occlusion in rats.

Normobaric hyperoxia (NBO) has been shown to extend the reperfusion window after focal cerebral ischemia. Employing diffusion (DWI)- and perfusion (PWI)-weighted magnetic resonance imaging (MRI), the effect of NBO (100% started at 30 mins after middle cerebral artery occlusion (MCAO)) on the spatiotemporal evolution of ischemia during and after permanent (pMCAO) and transient suture middle cerebral artery occlusion (tMCAO) was investigated (experiment 3). In two additional experiments, time window (experiment 1) and cell death pathways (experiment 2) were investigated in the pMCAO model. In experiment 1, NBO treatment reduced infarct volume at 24 h after pMCAO by 10% when administered for 3 h (P>0.05) and by 44% when administered for 6 h (P<0.05). In experiment 2, NBO acutely (390 mins, P<0.05) reduced in situ end labeling (ISEL) positivity in the ipsilesional penumbra but increased contralesional necrotic as well as caspase-3-mediated apoptotic cell death. In experiment 3, CBF characteristics and CBF-derived lesion volumes did not differ between treated and untreated animals, whereas the apparent diffusion coefficient (ADC)-derived lesion volume essentially stopped progressing during NBO treatment, resulting in a persistent PWI/DWI mismatch that could be salvaged by delayed (3 h) reperfusion. In conclusion, NBO (1) acutely preserved the perfusion/diffusion mismatch without altering CBF, (2) significantly extended the time window for reperfusion, (3) induced lasting neuroprotection in permanent ischemia, and (4) although capable of reducing cell death in hypoperfused tissue it also induced cell death in otherwise unaffected areas. Our data suggest that NBO may represent a promising strategy for acute stroke treatment.     

Volumetric evaluation of the ischemic lesion size with serial MRI in a transient MCAO model of the rat: comparison of DWI and T1WI

Magnetic resonance imaging (MRI) is applied in many studies on experimental cerebral ischemia in rodents to monitor the temporal evolution of ischemic damage. We report a protocol to evaluate the infarct size after middle cerebral artery occlusion with reperfusion (MCAO/R) in male Wistar rats. Imaging was performed with a 2.35 T scanner and we focused on diffusion-weighted imaging (DWI), T2-weighted imaging (T2WI) and postcontrast T1-weighted imaging (T1WI). We show the detailed procedure of volumetry, the contrast-to-noise ratio (CNR) and the intraindividual variability of infarct and hemispheric volumes at different reperfusion times. The presented method is of low variability if image contrast between ischemic and nonischemic tissue is very high, which is the case not only for all sequences at 8 and 12 h of reperfusion but also for DWI after 3 and 5 h of reperfusion. Furthermore, we describe the so-called mismatch region of lesion sizes depicted on DWI and postcontrast T1WI that suffers from cytotoxic edema but lacks contrast enhancement.     

Effect of the reperfusion after cerebral ischemia in neonatal rats using MRI monitoring

Cerebral hypoxia-ischemia is an important cause of brain injury in the newborn infant. Our purpose was to study magnetic resonance (MR) imaging changes in P7 rat brains submitted to permanent or reversible ischemia. Ischemia was induced by permanent electro-cauterization of the middle cerebral artery combined with a permanent or a transient (50 min) common carotid artery occlusion. The early events during ischemia and reperfusion were investigated by T2-weighted images (T2WI) at 1 and 3 h and by serial diffusion-weighted images (DWI) during 3 h in a 7 T magnet with a standard weighted diffusion sequence (b=1282.04 s mm(-2)) and a SEMS sequence. Within the first hour after MCA occlusion, the T2WI areas of contrast enhancement increased to a mean volume of 12.9+/-6.4%, a steady state still detected at 3 h after the ischemic onset (10.5+/-2.5%). Contrast enhancement in DWI increased as soon as 15 min of ischemia in all animals up to 50 min after CCA occlusion. In permanent ischemia, DWI abnormalities volume then increased more slowly from 50 min to 3 h after CCA occlusion (+25%, n=5). In reversible ischemia, the DWI abnormalities volume either moderately decreased and reached a plateau (-8.4%, n=4) or dramatically decreased (-53.0%, n=3). Both T2WI and DWI evidenced a "patchy" pattern of recovery as also shown on cresyl violet-stained sections. In contrast to the adult, early ischemic injury in P7 rat brains is detected as an increase in hyper-intensities both in T2WI and DWI. Our data indicate that reperfusion is able to block edema evolution after neonatal stroke and that early T2WI and more accurately DWI allow to distinguish between different patterns of injury in reversible ischemia.     

Diffusion- and perfusion-weighted magnetic resonance imaging of focal cerebral ischemia and cortical spreading depression under conditions of mild hypothermia

In a model of experimental stroke, we characterize the effects of mild hypothermia, an effective neuroprotectant, on fluid shifts, cerebral perfusion and spreading depression (SD) using diffusion- (DWI) and perfusion-weighted MRI (PWI). Twenty-two rats underwent 2 h of middle cerebral artery (MCA) occlusion and were either kept normothermic or rendered mildly hypothermic shortly after MCA occlusion for 2 h. DWI images were obtained 0.5, 2 and 24 h after MCA occlusion, and maps of the apparent diffusion coefficient (ADC) were generated. SD-like transient ADC decreases were also detected using DWI in animals subjected to topical KCl application (n=4) and ischemia (n=6). Mild hypothermia significantly inhibited DWI lesion growth early after the onset of ischemia as well as 24 h later, and improved recovery of striatal ADC by 24 h. Mild hypothermia prolonged SD-like ADC transients and further decreased the ADC following KCl application and immediately after MCA occlusion. Cerebral perfusion, however, was not affected by temperature changes. We conclude that mild hypothermia is neuroprotective and suppresses infarct growth early after the onset of ischemia, with better ADC recovery. The ADC decrease during SD was greater during mild hypothermia, and suggests that the source of the ADC is more complex than previously believed.     

Spectacular shrinking deficit: insights from multimodal magnetic resonance imaging after embolic middle cerebral artery occlusion in Sprague-Dawley rats.

Almost no data is available on the serial changes in the brain after spectacular shrinking deficit (SSD) that may help understand this relatively rare clinical phenomenon. Quantitative diffusion-(DWI), perfusion-(PWI), T(1)-(T1WI), T(2)-weighted (T2WI), and functional magnetic resonance imaging (fMRI) were performed before, during, and up to 7 days after embolic middle cerebral artery occlusion (eMCAO) in male Sprague-Dawley rats (n=9). Region of interest (ROI) analysis was used to evaluate structural and functional MR signal changes within three ROIs defined by the apparent diffusion coefficient (ADC), cerebral blood flow (CBF) signatures, and final tissue viability. DWI, PWI, and T2WI lesion volumes were calculated using previously established viability thresholds and final infarct volumes ascertained with 2,3,5-triphenyltetrazolium chloride (TTC) staining. Serial MRI demonstrated spontaneous reperfusion of initially hypoperfused MCA regions accompanied by substantial reduction of initial ADC and CBF lesions and gradual recovery of neurological outcome. Recovery rates of CBF/ADC abnormalities differed among ROIs. Functional magnetic resonance imaging showed persistent tissue dysfunction after the recovery of the CBF/ADC lesions. This study may facilitate our understanding of the pathophysiological mechanisms by which early, spontaneous reperfusion affects tissue fate and neurological function.     

Diffusion-weighted magnetic resonance imaging: rapid and quantitative detection of focal brain ischemia.

We examined serial changes of diffusion- (DWI) and T2-weighted (T2WI) magnetic resonance images 30 minutes to 3 hours after intraluminal suture occlusion of the middle cerebral artery (MCA) in eight rats and after sham occlusion in four. We correlated the abnormal areas on DWI and T2WI with postmortem areas of infarction determined by 2,3,5-triphenyltetrazolium chloride (TTC), 24 hours after the operation. The 30-minute DWI in each MCA-occluded rat demonstrated increased signal intensity in the ipsilateral MCA territory, while T2WI showed no changes. At 3 hours, the ipsilateral DWI signal intensity increased further and the area of abnormality slightly increased. In some animals, the 3-hour T2WI disclosed an area of hyperintensity significantly smaller than that seen on the 30-minute DWI. TTC staining demonstrated an extensive MCA infarction in all rats with permanent MCA occlusion, confirmed by hematoxylin and eosin staining. The percent infarcted area of coronal brain sections, as determined by TTC staining, correlated significantly with areas on similar DWI sections at both 30 minutes and 3 hours. Sham-occluded control animals did not display any changes on DWI, T2WI, or TTC staining. The present study suggests that DWI is a very sensitive modality for detecting early ischemic brain injury, being highly correlated with post-mortem area of infarction, and may be useful to assess pharmacologic intervention.     

Temporal evolution of ischemic injury evaluated with diffusion-, perfusion-, and T2-weighted MRI

OBJECTIVE: Ischemic lesions seen on diffusion-weighted imaging (DWI) are reversible if reperfusion is performed within minutes after the onset of ischemia. This study was designed to determine whether acute reversibility of DWI abnormalities is transient following brief temporary focal brain ischemia and to characterize the temporal evolution of in vivo ischemic lesions. METHODS: Eight rats were subjected to 30 minutes of temporary middle cerebral artery occlusion and underwent diffusion-, perfusion-, and T2-weighted MRI during occlusion; immediately after reperfusion; 30, 60, and 90 minutes after reperfusion; and 12, 24, 48, and 72 hours after reperfusion. Average apparent diffusion coefficient (ADCav) values and the cerebral blood flow index (CBFi) ratio were calculated in both the lateral caudoputamen and overlying cortex at each time point. The size of the in vivo ischemic abnormalities was calculated from the ADCav and the T2 maps. Postmortem triphenyltetrazolium chloride (TTC) staining was used to verify ischemic injury. RESULTS: Both the CBFi ratio and ADCav values declined significantly in the two regions during occlusion. The CBFi ratio recovered immediately after reperfusion and remained unchanged over 72 hours. However, ADCav values returned to normal at 60 to 90 minutes and secondarily decreased at 12 hours after reperfusion as compared with those in the contralateral hemisphere. The extent of the in vivo ischemic lesions maximized at 48 hours and was highly correlated with TTC-derived lesion size. CONCLUSIONS: Acute recovery of initial ADCav-defined lesions after reperfusion is transient, and secondary ADCav-defined lesions develop in a slow and delayed fashion.     

Nitric oxide synthase inhibitorN-nitro-l-arginine methyl ester decreases ischemic damage in reversible focal cerebral ischemia in hyperglycemic rats

We tested the hypothesis that the exacerbation of post-ischemic brain tissue injury associated with hyperglycemia in rats is due to toxic metabolism of nitric oxide. We used magnetic resonance imaging (MRI) techniques to measure neuronal and cerebrovascular injury in a 2-h transient focal cerebral ischemia model in normoglycemic and hyperglycemic rats at 3 and 24 h post-ischemia onset. We determined the effect of low dose (3 mg/kg i.p.) treatment with the nitric oxide synthase inhibitorN^G-nitro-l-arginine methyl ester (l-NAME). Compared to normoglycemia, preexisting hyperglycemia increased the volume of brain tissue exhibiting hyperintensity in diffusion weighted MRI (DWI) by factors of 5.6 and 6.2 at 3 h and 24 h post-ischemia, respectively. A similar increase in tissue volumes exhibiting hyperintense signal in T2-weighted MRI (T2WI) (3.3-fold and 5.6-fold) was observed. Cerebral blood volume MRI indicated a large focal no-reflow zone in hyperglycemic rats. Treatment withl-NAME eliminated the no-reflow zone in the hyperglycemic rats, and reduced tissue volumes of DWI hyperintensity by 86% and 93% at 3 h and 24 h, respectively. Similarly, tissue volumes of T2WI hyperintensity were reduced by 80% and 94% at 3 h and 24 h, respectively. Thus, nitric oxide is an important mediator in the exacerbation of post-ischemic brain injury in hyperglycemic rats. Inhibition of nitric oxide synthase limits edema formation, improves perfusion and reduces infarct volume.     

Nitric oxide synthase inhibitorN-nitro-l-arginine methyl ester decreases ischemic damage in reversible focal cerebral ischemia in hyperglycemic rats

We tested the hypothesis that the exacerbation of post-ischemic brain tissue injury associated with hyperglycemia in rats is due to toxic metabolism of nitric oxide. We used magnetic resonance imaging (MRI) techniques to measure neuronal and cerebrovascular injury in a 2-h transient focal cerebral ischemia model in normoglycemic and hyperglycemic rats at 3 and 24 h post-ischemia onset. We determined the effect of low dose (3 mg/kg i.p.) treatment with the nitric oxide synthase inhibitorN^G-nitro-l-arginine methyl ester (l-NAME). Compared to normoglycemia, preexisting hyperglycemia increased the volume of brain tissue exhibiting hyperintensity in diffusion weighted MRI (DWI) by factors of 5.6 and 6.2 at 3 h and 24 h post-ischemia, respectively. A similar increase in tissue volumes exhibiting hyperintense signal in T2-weighted MRI (T2WI) (3.3-fold and 5.6-fold) was observed. Cerebral blood volume MRI indicated a large focal no-reflow zone in hyperglycemic rats. Treatment withl-NAME eliminated the no-reflow zone in the hyperglycemic rats, and reduced tissue volumes of DWI hyperintensity by 86% and 93% at 3 h and 24 h, respectively. Similarly, tissue volumes of T2WI hyperintensity were reduced by 80% and 94% at 3 h and 24 h, respectively. Thus, nitric oxide is an important mediator in the exacerbation of post-ischemic brain injury in hyperglycemic rats. Inhibition of nitric oxide synthase limits edema formation, improves perfusion and reduces infarct volume.     

Characterizing the diffusion/perfusion mismatch in experimental focal cerebral ischemia

Diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) can rapidly detect lesions in acute ischemic stroke patients. The PWI volume is typically substantially larger than the DWI volume shortly after onset, that is, a diffusion/ perfusion mismatch. The aims of this study were to follow the evolution of the diffusion/ perfusion mismatch in permanent and 60- minute temporary focal experimental ischemia models in Sprague-Dawley rats using the intraluminal middle cerebral artery occlusion (MCAO) method. DWI and arterial spin-labeled PWI were performed at 30, 60, 90, 120, and 180 minutes after occlusion and lesion volumes (mm(3)) calculated At 24 hours after MCAO, and infarct volume was determined using triphenyltetrazolium chloride staining. In the permanent MCAO group, the lesion volume on the ADC maps was significantly smaller than that on the cerebral blood flow maps through the first 60 minutes after MCAO; but not after 90 minutes of occlusion. With 60 minutes of transient ischemia, the diffusion/perfusion mismatch was similar, but after reperfusion, the lesion volumes on ADC and cerebral blood flow maps became much smaller. There was a significant difference in 24- hour infarct volumes between the permanent and temporary occlusion groups.     

磁共振在大鼠脑缺血再灌注模型中的应用研究

【摘要】
目的 利用磁共振成像（magnetic resonance imaging,MRI）筛选合格的大鼠大脑中动脉闭塞（middle cerebral artery occlusion,MCAO）模型,分析大鼠脑缺血再灌损伤后表观弥散系数（apparent diffusion coefficient,ADC）及部分各向异性（fractional anisotropy,FA）指标的变化特征。
方法 制作SD大鼠MCAO模型,根据是否再灌注分为永久闭塞组和缺血再灌组,每组各9只,另设假手术组2只作为对照。对大鼠行磁共振T2、弥散加权成像（diffusion weighted imaging,DWI）、弥散张量成像（diffusion tensor imaging,DTI）和磁共振血管成像（magnetic resonance angiography,MRA）扫描,重建脑血管及计算相对ADC值和FA值,比较两组的相对ADC值和FA值。
结果 MRA可以显示大鼠脑血管的堵塞与再通,T2加权像可以观测到蛛网膜下腔出血。永久闭塞组比缺血再灌组的相对ADC值高,差异有显著性（0.657±0.140 vs 0.588±0.132,t＝2.27,P=0.048）;相对FA值高,差异有显著性（1.010±0.143 vs 0.915±0.111,t＝2.89,P=0.02）。
结论 利用MRA和T2加权像扫描可以筛选出合格的MCAO模型,MCAO永久闭塞组相对ADC值和FA值均高于缺血再灌注组。     

Permanent or transient chronic ischemic stroke in the non-human primate: behavioral, neuroimaging, histological, and immunohistochemical investigations

Using multimodal magnetic resonance imaging (MRI), behavioral, and immunohistochemical analyses, we examined pathological changes at the acute, sub-acute, and chronic stages, induced by permanent or temporary ischemia in the common marmoset. Animals underwent either permanent (pMCAO) or 3-h transient (tMCAO) occlusion of the middle cerebral artery (MCAO) by the intraluminal thread approach. MRI scans were performed at 1 h, 8, and 45 days after MCAO. Sensorimotor deficits were assessed weekly up to 45 days after MCAO. Immunohistological studies were performed to examine neuronal loss, astrogliosis, and neurogenesis. Remote lesions were analyzed using retrograde neuronal tracers. At day 8 (D8), the lesion defined on diffusion tensor imaging (DTI)–MRI and T2-MRI was significantly larger in pMCAO as compared with that in the tMCAO group. At D45, the former still displayed abnormal signals in T2-MRI. Post-mortem analyses revealed widespread neuronal loss and associated astrogliosis to a greater extent in the pMCAO group. Neurogenesis was increased in both groups in the vicinity of the lesion. Disconnections between the caudate and the temporal cortex, and between the parietal cortex and the thalamus, were observed. Sensorimotor impairments were more severe and long-lasting in pMCAO relative to tMCAO. The profile of brain damage and functional deficits seen in the marmoset suggests that this model could be suitable to test therapies against stroke.     

Broad-spectrum cation channel inhibition by LOE 908 MS reduces infarct volume in vivo and postmortem in focal cerebral ischemia in the rat

Cation channels conduct calcium, sodium and potassium, cations that are likely deleterious in the evolution of focal ischemic injury. We studied the effects of a novel, broad-spectrum inhibitor of several cation channels, LOE 908 MS, on acute ischemic lesion development with diffusion-weighted magnetic resonance imaging (DWI) and on cerebral perfusion with perfusion imaging (PI) in vivo and on cerebral infarct size using 2,3,5-triphenyltetrazolium chloride (TTC) staining postmortem. A total of 18 male Sprague-Dawley rats underwent 90 min of middle cerebral artery occlusion (MCAO) and were randomly and blindly assigned to either LOE 908 MS or vehicle starting 30 min after inducing focal ischemia and continuing for 4 h. Whole-brain DWI and multislice PI were done before initiation of treatment and repeated frequently for the next 3.5 h. DWI-derived lesion volume at 4 h showed a significant difference in favor of the drug treated group (P=0.03), whereas PI-derived perfusion deficit volumes did not significantly differ between the groups. The postmortem infarct volume at 24 h was significantly attenuated in the treated group in comparison to controls (P=0.0001) and neurological score was significantly better in the treated group (P<0.02). Blocking several distinct cation channels with LOE 908 MS significantly reduced infarct size and improved neurological outcome without observable adverse effects in this focal ischemia model.     

Feasibility of establishing cerebral ischemia models by using aerocyst-blocking bilateral ascending pharyngeal artery of piglets Imaging assessment

BACKGROUND: The cerebral ischemia and ischemia/reperfusion animal models are used to simulate the human cerebrovascular diseases is one of the popular topics of neurological science recently. To study the pathophysiology, pathogenesis, prophylaxis and treatment of ischemic cerebrovascular diseases and to establish the ideal animal model that is the most similar to the human cerebral ischemia, are the topics that the people generally cared about. OBJECTIVE: To evaluate the effects of aerocyst-blocking bilateral ascending pharyngeal artery on the establishment of cerebral ischemia models by using digital subtraction angiography (DSA), magnetic resonance diffusion-weighted imaging (DWI) and magnetic resonance perfusion-weighted imaging (PWI). DESIGN: Repetitive measure animal experiment. SETTING: Zhongshan Hospital Affiliated to Dalian University. MATERIALS: The experiment was carried out in the Animal Laboratory (Provincial Laboratory), Zhongshan Hospital of Dalian Univeristy from January to May 2006. A total of 14 domestic piglets, of 6 months old, weighing 12–15 kg, of either gender, were selected from Animal Experimental Center, Dalian University. Multistar T.O.P digital subtraction angiography machine was provided by Siemens Company, German. METHODS: Aerocyst-blocking bilateral ascending pharyngeal artery was used to establish cerebral ischemia models. And then, Multistar T.O.P. DSA was used for imaging of cerebral vessels before blocking, during blocking and at 0.5 and 2 hours after ischemia perfusion. GE Signa 1.5 T supraconduction magnetic resonance imaging was used for DWI examination; in addition, PWI was used based on focal sites and areas. Otherwise, magnetic resonance imaging (MRI) was used to detect signal changes of T1WI and T2WI in ischemic areas. MAIN OUTCOME MEASURES: Analytic results of DSA, DWI, PWI and MRI. RESULTS: All 14 experimental piglets were involved in the final analysis. ① DSA: The blood flow of bilateral ascending pharyngeal arteries and its branch were blocked at blocking phase, which restored 0.5 and 2 hours after reperfusion. ② DWI and PWI: There were no observable abnormalities in PWI and DWI at pre-blocking. Abnormal increased signals were found on both DWI and PWI at during and post-blocking. There were reduction in ADC and rCBF and delay in rTTP at all time points except pre-blocking. ③ MRI: There were no abnormal signals observable at any time of pre- and post-blocking in T1WI and T2WI. CONCLUSION: It is feasible to establish this kind of animal experimental models, and it can simulate the ischemic state; meanwhile, the existence and extent can be showed directly by DSA, DWI, and PWI.     

Clinical utility of diffusion-weighted magnetic resonance imaging in the assessment of ischemic stroke

Diffusion-weighted imaging (DWI) detects small changes in water diffusion that occur in ischemic brain. This study evaluated the clinical usefulness of a phase-navigated spin-echo DWI sequence compared with T2-weighted magnetic resonance imaging (T2W MRI) in patients with cerebral ischemia and assessed apparent diffusion coefficient (ADC) and T2-weighted imaging (T2WI) changes over time. ADC values and T2 ratios of image intensity were measured from the region of ischemia and from the corresponding contralateral brain region. The clinical histories of patients with DWI scans obtained over the course of 1 year were reviewed to ascertain whether DWI aided in clinical diagnosis or management. Of 103 scans obtained a mean of 10.4 days after symptom onset, DWI detected six lesions not seen on T2WI and discriminated two new infarcts from old lesions. DWI was most useful within 48 hours of the ictus. The evolution of ADC values and T2 ratios was evaluated in 26 cases with known symptom onset times. ADC values were low at less than 1 week after stroke onset and became elevated at chronic time points. T2 ratios were near normal acutely, increasing thereafter. DWI was superior to T2W MRI in detecting acute stroke, whereas both techniques assisted in determining lesion age.     

Functional, perfusion and diffusion MRI of acute focal ischemic brain injury.

Combined functional, perfusion and diffusion magnetic resonance imaging (MRI) with a temporal resolution of 30 mins was performed on permanent and transient focal ischemic brain injury in rats during the acute phase. The apparent diffusion coefficient (ADC), baseline cerebral blood flow (CBF), and functional MRI (fMRI) blood-oxygen-level-dependent (BOLD), CBF, and CMRO(2) responses associated with CO(2) challenge and forepaw stimulation were measured. An automated cluster analysis of ADC and CBF data was used to track the spatial and temporal progression of different tissue types (e.g., normal, 'at risk,' and ischemic core) on a pixel-by-pixel basis. With permanent ischemia (n=11), forepaw stimulation fMRI response in the primary somatosensory cortices was lost, although vascular coupling (CO(2) response) was intact in some animals. Control experiments in which the right common carotid artery was ligated without causing a stroke (n=8) showed that the delayed transit time had negligible effect on the fMRI responses in the primary somatosensory cortices. With temporary (15-mins, n=8) ischemia, transient CBF and/or ADC declines were observed after reperfusion. However, no T(2) or TTC lesions were observed at 24 h except in two animals, which showed very small subcortical lesions. Vascular coupling and forepaw fMRI response also remained intact. Finally, comparison of the relative and absolute fMRI signal changes suggest caution when interpreting percent changes in disease states in which the baseline signals are physiologically altered; quantitative CBF fMRI are more appropriate measures. This approach provides valuable information regarding ischemic tissue viability, vascular coupling, and functional integrity associated with ischemic injury and could have potential clinical applications.