Multimodal MR examination in acute ischemic stroke

In recent years, combined diffusion-weighted imaging (DWI) with perfusion imaging (PI) has become an important investigational tool in the acute phase of ischemic stroke, as it may differentiate reversible from irreversible brain tissue damage. We consecutively examined 20 subjects within 12 h of stroke onset using a multiparametric magnetic resonance (MR) examination consisting of DWI, mean transit time (MTT) as PI parameter, and MR angiography (MRA). T2-weighted and fluid-attenuated inversion recovery (FLAIR) on day 7 were also acquired in order to obtain final infarct volume. The following MR parameters were considered: volumetric measures of lesion growth and MTT abnormalities, quantification of regional apparent diffusion coefficient (ADC) and visual inspection of MRA findings. Our results showed: (1) an acute DWI lesion was not predictive of lesion growth and the DWI abnormality did not represent the irreversibly infarcted tissue; (2) ADC values in the ischemic penumbra could not predict tissue at risk; (3) the DWI–PI mismatch did not predict lesion growth, and the PI abnormality overestimated the amount of tissue at risk; and (4) patients with proximal middle cerebral artery occlusion had greater initial and final infarct volumes. This study did not demonstrate the prognostic value of a multimodal MR approach in early ischemic stroke; MRA alone provided predictive information about the volumetric evolution of the lesion.     

Predicting final infarct size using acute and subacute multiparametric MRI measurements in patients with ischemic stroke

PURPOSE: To identify early MRI characteristics of ischemic stroke that predict final infarct size three months poststroke. MATERIALS AND METHODS: Multiparametric MRI (multispin echo T2-weighted [T2W] imaging, T1-weighted [T1W] imaging, and diffusion-weighted imaging [DWI]) was performed acutely (<24 hours), subacutely (three to five days), and at three months. MRI was processed using maps of apparent diffusion coefficient (ADC), T2, and a self-organizing data analysis (ISODATA) technique. Analyses began with testing for individual MRI parameter effects, followed by multivariable modeling with assessment of predictive ability (R(2)) on final infarct size. RESULTS: A total of 45 patients were studied, 15 of whom were treated with tissue plasminogen activator (tPA) before acute MRI. The acute DWI and DWI-ISODATA mismatch lesion size, and the interactions of ADC, T2, and T2W imaging lesion with tPA remained in the final multivariable model (R(2) = 70%). A large acute DWI lesion or DWI < ISODATA lesion independently predicted increase in the final infract size, with predictive ability 68%. Predictive ability increased (R(2) = 83%) when subacute MRI parameters were included along with acute DWI, DWI-ISODATA mismatch, and acute T2W image lesion size by tPA treatment interaction. Subacute DWI > acute DWI lesion size predicted an increased final infarct size (P < 0.01). CONCLUSION: Acute-phase DWI and DWI-ISODATA mismatch strongly predict the final infarct size. An acute-to-subacute DWI lesion size change further increases the predictive ability of the model.     

A comparison of images generated from diffusion-weighted and diffusion-tensor imaging data in hyper-acute stroke

PURPOSE: To compare isotropic (combined diffusion-weighted image [CMB], apparent diffusion coefficient [ADC], TRACE, exponential ADC [eADC], and isotropically-weighted diffusion image [isoDWI]) and anisotropic (relative anisotropy [RA], fractional anisotropy [FA], and volume ratio [VR]) diffusion images collected with fast magnetic resonance (MR) diffusion-weighted (DWI) and diffusion-tensor (DTI) acquisition strategies (each less than one minute) in hyper-acute stroke. MATERIALS AND METHODS: Twenty-one patients suffering from ischemic stroke-imaged within six hours of symptom onset using both DWI and DTI-were analyzed. Regions of interest were placed in the ischemic lesion and in normal contralateral tissue and the percent difference in image intensity was calculated for all nine generated images. RESULTS: The average absolute percent changes for the isotropic strategies were all > 38%, with isoDWI found to have a difference of 50.7% +/- 7.9% (mean +/- standard error, P < 0.001). The ADC maps had the most significant difference (-42.4% +/- 2.0%, P < 0.001, coefficient of variation = 0.22). No anisotropic images had significant differences. CONCLUSION: Anisotropic maps do not consistently show changes in the first six hours of ischemic stroke; therefore, isotropic maps, such as those obtained using DWI, are more appropriate for detecting hyper-acute stroke. Anisotropic images, however, may be useful to differentiate hyper-acute stroke from acute and sub-acute stroke.     

Multiphasic perfusion computed tomography in hyperacute ischemic stroke: comparison with diffusion and perfusion magnetic resonance imaging

PURPOSE: The purpose of this study was to compare multiphasic perfusion computed tomography (CT) with diffusion and perfusion magnetic resonance imaging (MRI) in predicting final infarct volume, infarct growth, and clinical severity in patients with hyperacute ischemia untreated by thrombolytic therapy. METHOD: Multiphasic perfusion CT was performed in 19 patients with ischemic stroke within 6 hours of symptom onset. Two CT maps of peak and total perfusion were generated from CT data. Diffusion-weighted imaging (DWI) and perfusion MRI were obtained within 150 minutes after CT. Lesion volumes on CT and MRI were compared with final infarct volume and clinical scores, and mismatch on CT or MRI was compared with infarct growth. RESULTS: The lesion volume on the CT total perfusion map strongly correlated with MRI relative cerebral blood volume (rCBV), and that on the CT peak perfusion map strongly correlated with MRI relative cerebral blood flow (rCBF) and rCBV (P < 0.001). The lesion volume on unenhanced CT or DWI moderately correlated with final infarct volume, but only lesion volume on unenhanced CT weakly correlated with baseline clinical scores (P = 0.024). The lesion volumes on the CT peak perfusion map and MRI rCBF similarly correlated with final infarct volume and clinical scores and more strongly than those on mean transit time (MTT) or time to peak (TTP). DWI-rCBF or CT mismatch was more predictive of infarct growth than DWI-MTT or DWI-TTP mismatch. CONCLUSION: Multiphasic perfusion CT is useful and of comparable utility to diffusion and perfusion MRI for predicting final infarct volume, infarct growth, and clinical severity in acute ischemic stroke.     

Real-time diffusion-perfusion mismatch analysis in acute stroke

Diffusion-perfusion mismatch can be used to identify acute stroke patients that could benefit from reperfusion therapies. Early assessment of the mismatch facilitates necessary diagnosis and treatment decisions in acute stroke. We developed the RApid processing of PerfusIon and Diffusion (RAPID) for unsupervised, fully automated processing of perfusion and diffusion data for the purpose of expedited routine clinical assessment. The RAPID system computes quantitative perfusion maps (cerebral blood volume, CBV; cerebral blood flow, CBF; mean transit time, MTT; and the time until the residue function reaches its peak, T(max)) using deconvolution of tissue and arterial signals. Diffusion-weighted imaging/perfusion-weighted imaging (DWI/PWI) mismatch is automatically determined using infarct core segmentation of ADC maps and perfusion deficits segmented from T(max) maps. The performance of RAPID was evaluated on 63 acute stroke cases, in which diffusion and perfusion lesion volumes were outlined by both a human reader and the RAPID system. The correlation of outlined lesion volumes obtained from both methods was r(2) = 0.99 for DWI and r(2) = 0.96 for PWI. For mismatch identification, RAPID showed 100% sensitivity and 91% specificity. The mismatch information is made available on the hospital's PACS within 5-7 min. Results indicate that the automated system is sufficiently accurate and fast enough to be used for routine care as well as in clinical trials.     

Development of brain infarct volume as assessed by magnetic resonance imaging (MRI): follow-up of diffusion-weighted MRI lesions

PURPOSE: To investigate the development of ischemic brain lesions, as present in the acute stroke phase, by diffusion-weighted magnetic resonance imaging (DWI), and in the subacute and chronic phases until up to four months after stroke, in fluid-attenuated inversion recovery (FLAIR)- and T2-weighted (T2W) magnetic resonance (MR) images. MATERIALS AND METHODS: Twelve consecutive patients with their first middle cerebral artery (MCA) infarction were included. Lesion volumes were assessed on T2W images recorded with a turbo spin echo (TSE) and on images recorded with the FLAIR sequence on average on day 8 and after about four months. They were compared with acute lesion volumes in perfusion and DWI images taken within 24 hours of stroke onset. RESULTS: On day 8, lesion volumes in images obtained with FLAIR exceeded the acute infarct volumes in DWI. The chronic lesion volumes were almost identical in T2W and FLAIR images but significantly reduced compared with the acute DWI lesions. The lesion volumes assessed on DWI images correlated highly with the lesions in the images obtained with TSE or FLAIR, as did the lesions in the images obtained with FLAIR and TSE. The secondary lesion shrinkage was accompanied by ventricular enlargement and perilesional sulcal widening, as most clearly visible in the images obtained with FLAIR. CONCLUSION: Our results show that the acute DWI lesions are highly predictive for the infarct lesion in the chronic stage after stroke despite a dynamic lesion evolution most evident in MR images obtained with FLAIR.     

Diffusion-weighted MR imaging in acute ischemia: value of apparent diffusion coefficient and signal intensity thresholds in predicting tissue at risk and final infarct size

BACKGROUND AND PURPOSE: Identifying tissue at risk for infarction is an important goal of stroke imaging. This study was performed to determine whether pixel-based apparent diffusion coefficient (ADC) and signal intensity ratio are helpful diffusion-weighted (DW) imaging metrics to predict tissue at risk for infarction. METHODS: Twelve patients presenting with acute hemispheric strokes underwent DW imaging within 7 hours of symptom onset. Region of interest (ROI), pixel-based ADC, and signal intensity analyses were performed at initial DW imaging to assess area of infarct growth, final infarct area, and normal tissue. RESULTS: Pixel-based analysis was less accurate than ROI-based analysis for evaluating infarct growth or final infarct with ADC, ADC ratio, and signal intensity ratios. In pixel-based analysis, signal intensity ratios were better than ADCs or ADC ratios for identifying tissue at risk (accuracy, 67.4%) and for predicting final infarct (accuracy, 79.9%). Linear regression analysis demonstrated a strong correlation between lesion volume on quantitative DW images or ADC maps and final infarct volume (P < .001). When receiver operating characteristic (ROC) curves were used to determine optimal cutoffs for ADC and DW image values, the region of infarct growth was significantly correlated with only the mismatch between initial qualitative DW image and quantitative DW image signal intensity ratio (cutoff value, 1.19; R = 0.652; P = .022). CONCLUSION: Pixel-based thresholds applied to ADC or DW image signal intensity maps were not accurate prognostic measures of tissue at risk. Quantitative DW images or ADC maps may provide added information not obtained by visual inspection of the qualitative DW image map.     

Time evolution of cerebral perfusion and apparent diffusion coefficient measured by magnetic resonance imaging in a porcine stroke model

PURPOSE: To demonstrate the feasibility of sequential diffusion-weighted (DW) and perfusion-weighted (PW) magnetic resonance imaging (MRI) of a recently developed porcine stroke model and to evaluate the evolution of cerebral perfusion and the apparent diffusion coefficient (ADC) over time. Materials and Methods In five pigs, DW imaging (DWI) and PW imaging (PWI) was carried out for 7 hours after stroke onset, starting 1 hour after middle cerebral artery occlusion (MCAO). RESULTS: The DWI lesion volume increased significantly with time, and final DWI lesion volume correlated well with lesion area on histological sections (r = 0.910). T2 changes could be recognized 3 hours after stroke onset. At 1 hour the ADC ratio (ischemic lesion/contralateral side) was reduced to 0.81 in the caudate-putamen and to 0.87 in the cortex, and the cerebral blood flow ratio was reduced to 0.40 in the caudate-putamen and 0.51 in the cortex. CONCLUSION: The level of flow reduction in the caudate-putamen and the cortex after 1 hour is in good correlation with human thresholds of irreversible and reversible ischemic damage, and accordingly, this model might be a model for mechanisms of infarct evolution and therapeutic intervention.     

ADC在急性缺血性卒中缺血半暗带判定中的价值

目的:探讨ADC对确定急性缺血性卒中缺血半暗带的价值。方法:选择33例超急性、急性脑梗死患者,采用全自动图像分析系统,以DWI图像计算得到的ADC图作为输入数据,来判断缺血半暗带的存在(简称为ADC方法),并在2～30d内复查T2WI确定最终梗死范围,测量梗死中心区、缺血半暗带及对侧镜像区的扩散变化。结果:梗死中心区与缺血半暗带ADC平均值分别为4.38×10-4 mm2/s、6.81×10-4 mm2/s,rADC平均值分别为0.56及0.85,梗死中心区ADC及rADC均明显降低,缺血半暗带ADC及rADC轻度下降,二者之间差异有统计学意义。结论:ADC方法对确定缺血半暗带具有潜在的临床实用价值,有望成为一种简便易行的确定缺血半暗带的方法。     

Comparison of perfusion computed tomography with diffusion-weighted magnetic resonance imaging in hyperacute ischemic stroke

OBJECTIVE: In this study, perfusion CT and diffusion-weighted magnetic resonance imaging (DWI) were compared as means of assessing the ischemic brain in hyperacute stroke. METHODS: Twenty patients with ischemic stroke underwent perfusion computed tomography (CT) and magnetic resonance imaging (MRI) studies <3 hours after stroke onset. Cerebral blood flow thresholds were used to delineate the ischemic lesion, penumbra, and infarct. Correlations between the volume of the hypoperfused areas, the abnormality volume in admission DWI and follow-up CT/MRI studies, and the clinical National Institutes of Health Stroke Scale (NIHSS) scores were performed. RESULTS: The volume of the ischemic (core and penumbra) lesion on admission perfusion CT was correlated with the volume of admission DWI abnormalities (r=0.89, P=0.001). The infarcted core tissue volume (on admission CT) correlated more strongly (r=0.77, P=0.0001) than the admission DWI abnormality volume (r=0.69, P=0.002) with the follow-up infarct volume on fluid-attenuated inversion recovery images. A correlation was demonstrated between infarct volume in perfusion CT and follow-up DWI abnormality volume (r=0.89, r=0.77, P=0.002). Significant correlations were found between ischemic and infarct region volumes in perfusion CT and NIHSS admission and follow-up scores (P < or = 0.01). CONCLUSIONS: Both imaging modalities provide a sufficient assessment of the hyperacute brain infarct, with significant correlation between them and the clinical condition at admission. Perfusion CT allows differentiation of the penumbra and infarct core region with significant predictive value of follow-up infarct volume and clinical outcome.     

Evolution of hyperacute stroke over 6 hours using serial MR perfusion and diffusion maps

Purpose

To develop an appropriate method to evaluate the time‐course of diffusion and perfusion changes in a clinically relevant animal model of ischemic stroke and to examine lesion progression on MR images. An exploration of acute stroke infarct expansion was performed in this study by using a new methodology for developing time‐to‐infarct maps based on the time at which each voxel becomes infarcted. This enabled definition of homogeneous regions from the heterogeneous stroke infarct.

Materials and Methods

Time‐to‐infarct maps were developed based on apparent diffusion coefficient (ADC) changes. These maps were validated and then applied to blood flow and time‐to‐peak maps to examine perfusion changes.

Results

ADC stroke infarct showed different evolution patterns depending on the time at which that region of tissue infarcted. Applying the time‐to‐infarct maps to the perfusion maps showed localized perfusion evolution characteristics. In some regions, perfusion was immediately affected and showed little change over the experiment; however, in some regions perfusion changes were more dynamic.

Conclusion

Results were consistent with the diffusion‐perfusion mismatch hypothesis. In addition, characteristics of collateral recruitment were identified, which has interesting stroke pathophysiology and treatment implications. J. Magn. Reson. Imaging 2009;29:1262–1270. © 2009 Wiley‐Liss, Inc.     

Identifying lesion growth with MR imaging in acute ischemic stroke

PURPOSE: To determine whether different MR diffusion- and perfusion-weighted imaging (DWI and PWI) parameters are important in distinguishing lesion growth from the acute lesion and from oligemia. MATERIALS AND METHODS: MR DWI and PWI were acquired from thirteen patients. We defined three regions: (i) LESION - intersection of acute and final lesions, (ii) GROWTH - portion of final lesion not part of acute lesion, and (iii) OLIGEMIA - region of perfusion abnormality not part of either the acute or final lesions. We used logistic regression modeling to distinguish GROWTH from LESION and from OLIGEMIA on a voxel-wise basis using DWI- and PWI-based parameters. Final models were selected based on the Wald statistic and validated by cross-validation using the mean (+/- standard deviation) area under the curve (AUC) from receiver operating characteristic analysis. RESULTS: The final model for differentiating GROWTH from LESION included DWI, the apparent diffusion coefficient (ADC), cerebral blood flow (CBF) and tissue type (AUC = 0.939 +/- 0.028). The final model for differentiating GROWTH from OLIGEMIA included DWI, ADC, CBF, and time-to-peak (AUC = 0.793 +/- 0.106). CONCLUSION: Different MR parameters are important in differentiating lesion growth from acute lesion and from oligemia in acute ischemic stroke.     

Time course of cerebral infarction in the middle cerebral arterial territory: deep watershed versus territorial subtypes on diffusion-weighted MR images

PURPOSE: To examine possible differences between the evolution of cerebral watershed infarction (WI) and that of territorial thromboembolic infarction (TI) by using diffusion-weighted (DW) and T2-weighted magnetic resonance (MR) images and apparent diffusion coefficient (ADC) maps. MATERIALS AND METHODS: Fourteen patients with TI and nine with WI underwent MR imaging from the acute to chronic infarction stages. ADC maps were derived from DW images. Lesion-to-normal tissue signal intensity ratios on ADC maps (rADC), echo-planar T2-weighted images, and DW images were calculated. Lesion volumes at acute or early subacute infarction stages were measured on DW images, and final lesion volumes were estimated on fluid-attenuated inversion-recovery images. RESULTS: Analysis of variance revealed a significant difference in temporal evolution patterns of rADC between WI and TI (P <.001). rADC pseudonormalization following TI began about 10 days after symptom onset, but that following WI did not occur until about 1 month after symptom onset. The Pearson correlation coefficient between final and initial infarct volumes was 0.9899 for both infarction subtypes, indicating that the initial ischemic injury volume measured at the acute or early subacute stage predicted the final lesion volume fairly well. CONCLUSION: The evolution time of ADC is faster for TI than for WI. This difference, which likely originates from the different pathophysiologic and hemodynamic features of the two infarction types, might account for the relatively large range of ADC values reported for the time course of ischemic strokes.     

Improving the prediction of final infarct size in acute stroke with bolus delay-corrected perfusion MRI measures

PURPOSE: To investigate whether bolus delay-corrected dynamic susceptibility contrast (DSC) perfusion MRI measures allowed a more accurate estimation of eventual infarct volume in 14 acute stroke patients using a predictive tissue classifier algorithm. MATERIALS AND METHODS: Tissue classification was performed using a expectation maximization and k-means clustering algorithm utilizing diffusion and T2 measures (diffusion-weighted imaging [DWI], apparent diffusion coefficient [ADC], and T2) combined with uncorrected perfusion measures cerebral blood flow ((CBF) and mean transit time [MTT]), bolus delay-corrected perfusion measures (cCBF and cMTT), and bolus delay-corrected perfusion indices (cCBF and cMTT with bolus delay). RESULTS: The mean similarity index (SI), a kappa-based correlation statistic reflecting the pixel-by-pixel classification agreement between predicted and 30-day T2 lesion volumes, were 0.55 +/- 0.19, 0.61 +/- 0.15 (P < 0.02) and 0.60 +/- 0.17 (P <0.03), respectively. Spearman's correlation coefficients, comparing predicted and final lesion volumes were 0.56 (P < 0.05), 0.70 (P < 0.01), and 0.84 (P < 0.001), respectively. We found a more significant correlation between predicted infarct volumes derived from bolus delay-corrected perfusion measures than from conventional perfusion measures when combined with diffusion measures and compared with final lesion volumes measured on 30-day T2 MRI scans. CONCLUSION: Bolus delay-corrected perfusion measures enable an improved prediction of infarct evolution and evaluation of the hemodynamic status of neuronal tissue in acute stroke.     

Final infarct size after acute stroke: prediction with flow heterogeneity

PURPOSE: To compare acute measurements of flow heterogeneity (FH) and mean transit time (MTT) with follow-up data to determine which method yields better predictive measures of final infarct volumes. MATERIALS AND METHODS: Twenty-three patients with symptoms of stroke underwent magnetic resonance (MR) imaging during the acute stage, and the tissue at risk was estimated from MTT maps and maps generated by means of detecting abnormal FH. Final infarct volumes were calculated from T2-weighted follow-up MR image measurement. The Wilcoxon signed rank test was performed to compare the two predictive maps (MTT and FH) with T2-weighted follow-up maps. RESULTS: Eleven (48%) patients experienced infarct growth. Both the MTT and the FH maps enabled prediction of 10 of these cases. There were five false-positive cases with MTT measurement but three with FH measurement. In terms of predicting final infarct volumes, the final infarct size on the MTT maps was overestimated by 75%. The final infarct size on the FH maps also was overestimated, but by only 15%. MTT map measurements were significantly different from follow-up MR image measurements (P =.005), but FH map measurements were not (P =.059). CONCLUSION: FH maps may enable more precise prediction of final infarct volume in stroke patients.     

Effect of the arterial input function on the measured perfusion values and infarct volumetric in acute cerebral ischemia evaluated by perfusion computed tomography

OBJECTIVES: We sought to evaluate the accuracy of the perfusion computed tomography (PCT) deconvolution-based brain perfusion measurements and the lesions' (infarct and penumbra) volumetric with regard to arterial input function (AIF) selection in patients with acute stroke. MATERIALS AND METHODS: Eighteen consecutive patients with symptoms of acute stroke underwent PCT at admission. Follow-up magnetic resonance imaging was obtained in all patients after 3.6 +/- 1.7 days (range, 1.5-6 days). PCT maps were generated focusing on the anterior cerebral artery (ACA) and branches of the middle cerebral artery (MCA) ipsilateral and contralateral to the ischemic lesion as AIFs. Infarct, penumbra, and total ischemic lesion were delineated on cerebral blood flow (CBF) maps. CBF, cerebral blood volume (CBV), and mean transit time (MTT) were calculated in the ischemic regions as provided by the 3 different AIFs, the normality test was applied for the obtained parameters, and the values were correlated (Pearson's correlation coefficient). Volumes of the ischemic regions (as obtained by the different AIFs) also were correlated and compared (paired t test) to the follow-up infarct volume. RESULTS: The CBF and CBV values obtained by the different AIFs in the infarct, penumbra, and total ischemic lesion were significantly correlated (r=0.94-0.96, P相似文献   

Neuroprotective effects of an immunosuppressant agent on diffusion/perfusion mismatch in transient focal ischemia.

The immunosuppressant FK506 (tacrolimus) exerts potent neuroprotection following focal ischemia in animals; however, the separate effects of FK506 on the ischemic core and penumbra have not been reported. The ischemic penumbra is clinically defined as the difference between a large abnormal area on perfusion-weighted imaging (PWI) and a smaller lesion on diffusion-weighted imaging (DWI). The goal of this study was to determine the effect of FK506 on DWI/PWI match and mismatch areas in transient focal ischemia in rats. Twelve rats were subjected to 1 hr of transient middle cerebral artery (MCA) occlusion, and given an intravenous injection of a placebo (N = 6) or 1 mg/kg FK506 (N = 6) immediately before reperfusion. Magnetic resonance imaging (MRI) was performed during MCA occlusion, and 0.5, 1, and 24 hr after reperfusion. FK506 significantly protected the ischemic brain only in the mismatch cortex where the initial apparent diffusion coefficient (ADC) was normal and there was a mild reduction of cerebral blood flow (CBF). This is the first report to describe the protective effects of FK506 on ischemic penumbra, as measured by DWI/PWI mismatch. The findings provide direct evidence for the utility of DWI/PWI mismatch as a guideline for therapeutic intervention with FK506.     

Vascular occlusion sites determine differences in lesion growth from early apparent diffusion coefficient lesion to final infarct

BACKGROUND AND PURPOSE: Occlusion of major cerebral arteries is the primary source of tissue damage in ischemic stroke and the target of thrombolytic therapy. We hypothesized that large infarcts in more proximal vascular occlusions correspond with substantially increased ischemic lesions shown on initial apparent diffusion coefficient (ADC) maps. METHODS: Initial ADC lesions in 120 patients with acute ischemic stroke were analyzed within 6 hours of stroke onset. Patients were categorized on the basis of vascular occlusion, as shown on MR angiography. Lesion volumes were determined by using manual delineation (ADC(man)) and a threshold method for ADC values (<550 x 10(-9) mm(2)/s(-1), ADC(<550)). Infarct volumes were analyzed by using T2-weighted (n = 109) or CT (n = 11) images obtained on days 5-8. RESULTS: Median lesion volumes for ADC(<550), ADC(man), and infarcts, respectively, were as follows: proximal internal carotid artery (ICA)/middle cerebral artery (MCA) occlusions, 10, 23, and 32 cm(3); carotid-T occlusions, 11, 37, and 138 cm(3); MCA trunk occlusions, 11, 27, and 44 cm(3)); and MCA branch occlusions 8, 27, and 21 cm(3). Initial ADC lesion volumes were different only between the carotid T and the MCA branch (P < .05). On days 5-8, infarct volumes decreased from proximal to distal sites (P < .05), with the exception of MCA trunk versus proximal ICA/MCA occlusions. Recanalization rate in carotid-T occlusion was significantly lower than those of all other occlusion types. CONCLUSION: Initial ADC lesions can be small, even in patients with proximal vascular occlusions. These patients develop considerably large infarctions, suggesting a high potential for infarct growth. This growth might be averted with improved early recanalization of proximal vascular occlusions.     

Assessment of Tissue Viability Using Diffusion- and Perfusion-Weighted MRI in Hyperacute Stroke

Objective

The aim of this study was to investigate the relationship between the diffusion and perfusion parameters in hyperacute infarction, and we wanted to determine the viability threshold for the ischemic penumbra using diffusion- and perfusion-weighted imaging (DWI and PWI, respectively).

Materials and Methods

Both DWI and PWI were performed within six hours from the onset of symptoms for 12 patients who had suffered from acute stroke. Three regions of interest (ROIs) were identified: ROI 1 was the initial lesion on DWI; ROI 2 was the DWI/PWI mismatch area (the penumbra) that progressed onward to the infarct; and ROI 3 was the mismatch area that recovered to normal on the follow-up scans. The ratios of apparent diffusion coefficient (ADC), the relative cerebral blood volume (rCBV), and the time to peak (TTP) were calculated as the lesions'' ROIs divided by the contralateral mirror ROIs, and these values were then correlated with each other. The viability threshold was determined by using the receiver operating characteristic (ROC) curves.

Results

For all three ROIs, the ADC ratios had significant linear correlation with the TTP ratios (p < 0.001), but not with the rCBV ratios (p = 0.280). There was no significant difference for the ADC and rCBV ratios within the ROIs. The mean TTP ratio/TTP delay between the penumbras'' two ROIs showed a significant statistical difference (p < 0.001). The cutoff value between ROI 2 and ROI 3, as the viability threshold, was a TTP ratio of 1.29 (with a sensitivity and specificity of 86% and 73%, respectively) and a TTP delay of 7.8 sec (with a sensitivity and specificity of 84% and 72%, respectively).

Conclusion

Determining the viability thresholds for the TTP ratio/delay on the PWI may be helpful for selecting those patients who would benefit from the various therapeutic interventions that can be used during the acute phase of ischemic stroke.     

水通道蛋白磁共振分子成像对脑缺血半暗带的评价

目的探讨多b值磁共振扩散加权(MR-DWI)水通道蛋白分子成像(AQP-MRI)对脑缺血半暗带的诊断价值。材料与方法将30只SD大鼠按随机区组设计法分为缺血组(25只,缺血1、3、6、24、48 h各5只)和对照组(5只),缺血组经历1h短暂性大脑中动脉栓塞(MCAO)建立脑缺血模型,两组分别行多模态MRI扫描,采集T2加权液体衰减反转恢复成像(T2-FLAIR)、扩散加权成像(DWI)、动脉自旋标记(ASL)及AQP-MRI(18b值DWI)图像。将AQP-MRI与T2-FLAIR不匹配的区域与传统DWI/T2-FLAIR不匹配和ASL/DWI不匹配作比较,验证AQP-MRI对缺血半暗带的诊断价值,并结合组织病理学进行评价。结果对照组在每个时间点各序列均未见异常信号。缺血组24 h内,AQP-MRI/T2-FLAIR不匹配面积与DWI/T2-FLAIR不匹配面积比较,差异有统计学意义(P<0.001);6 h内,AQP-MRI/T2-FLAIR不匹配面积与ASL/DWI不匹配面积比较,差异有统计学意义(P=0.001)。24 h内半暗带区相对比值与梗死区相对比值及正常脑组织相对比值比较,差异均有统计学意义(P均<0.001),组织病理学结果显示,半暗带区是正常脑组织向坏死转变的过渡。结论与传统的不匹配相比,AQP-MRI/T2-FLAIR不匹配可多层次、更精准地实时动态显示缺血半暗带。AQP-MRI与T2-FLAIR相结合可对缺血半暗带的评价提供有价值的影像学信息。