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.     

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.     

Predicting cerebral ischemic infarct volume with diffusion and perfusion MR imaging

BACKGROUND AND PURPOSE: Diffusion and perfusion MR imaging have proved useful in the assessment of acute stroke. We evaluated the utility of these techniques in detecting acute ischemic infarction and in predicting final infarct size. METHODS: Diffusion and hemodynamic images were obtained in 134 patients within a mean of 12.3 hours of onset of acute ischemic stroke symptoms. We retrospectively reviewed patient radiology reports to determine the presence or absence of lesion identification on initial diffusion- (DW) and perfusion-weighted (PW) images. Radiologists were not blinded to the initial clinical assessment. For determination of sensitivity and specificity, the final discharge diagnosis was used as the criterion standard. Neurologists were not blinded to the DW or PW imaging findings. In 81 patients, acute lesions were compared with final infarct volumes. RESULTS: Sensitivities of DW imaging and cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) perfusion parameters were 94%, 74%, 84%, and 84%, respectively. Specificities of DW imaging, CBV, CBF, and MTT were 96%, 100%, 96%, and 96%, respectively. Results were similar in 93 patients imaged within 12 hours. In 81 patients with follow-up, regression analysis yielded r(2) = 0.9, slope = 1.24 for DW imaging; r(2) = 0.84, slope = 1.22 for CBV; r(2) = 0.35, slope = 0.44 for CBF; and r(2) = 0.22, slope = 0.32 for MTT, versus follow-up volume. A DW-CBV mismatch predicted additional lesion growth, whereas DW-CBF and DW-MTT mismatches did not. Results were similar in 60 patients imaged within 12 hours. CONCLUSION: Diffusion and hemodynamic images are sensitive and specific for detecting acute infarction. DW imaging and CBV best predict final infarct volume. DW-CBV mismatch predicts lesion growth into the CBV abnormality. CBF and MTT help identify additional tissue with altered perfusion but have lower correlation with final volume.     

Predicting stroke evolution: comparison of susceptibility-weighted MR imaging with MR perfusion

Objectives

To investigate the ability of susceptibility-weighted imaging (SWI) to predict stroke evolution in comparison with perfusion-weighted imaging (PWI).

Methods

In a retrospective analysis of 15 patients with non-lacunar ischaemic stroke studied no later than 24?h after symptom onset, we used the Alberta Stroke Program Early CT Score (ASPECTS) to compare lesions on initial diffusion-weighted images (DWI), SWI, PWI and follow-up studies obtained at least 5?days after symptom onset. The National Institutes of Health Stroke Scale scores at entry and stroke risk factors were documented. The clinical–DWI, SWI–DWI and PWI–DWI mismatches were calculated.

Results

SWI–DWI and mean transit time (MTT)–DWI mismatches were significantly associated with higher incidence of infarct growth (P?=?0.007 and 0.028) and had similar ability to predict stroke evolution (P?=?1.0). ASPECTS values on initial DWI, SWI and PWI were significantly correlated with those on follow-up studies (P?≤?0.026) but not associated with infarct growth. The SWI ASPECTS values were best correlated with MTT ones (ρ?=?0.8, P?Conclusions SWI is an alternative to PWI to assess penumbra and predict stroke evolution. Further prospective studies are needed to evaluate the role of SWI in guiding thrombolytic therapy. Key Points ? SWI can provide perfusion information comparable to MTT ? SWI–DWI mismatch can indicate ischaemic penumbra ? SWI–DWI mismatch can be a predictor for stroke evolution     

Accuracy of CT cerebral perfusion in predicting infarct in the emergency department: lesion characterization on CT perfusion based on commercially available software

This study aims to assess the diagnostic accuracy of a single vendor commercially available CT perfusion (CTP) software in predicting stroke. A retrospective analysis on patients presenting with stroke-like symptoms within 6 h with CTP and diffusion-weighted imaging (DWI) was performed. Lesion maps, which overlays areas of computer-detected abnormally elevated mean transit time (MTT) and decreased cerebral blood volume (CBV), were assessed from a commercially available software package and compared to qualitative interpretation of color maps. Using DWI as the gold standard, parameters of diagnostic accuracy were calculated. Point biserial correlation was performed to assess for relationship of lesion size to a true positive result. Sixty-five patients (41 females and 24 males, age range 22–92 years, mean 57) were included in the study. Twenty-two (34 %) had infarcts on DWI. Sensitivity (83 vs. 70 %), specificity (21 vs. 69 %), negative predictive value (77 vs. 84 %), and positive predictive value (29 vs. 50 %) for lesion maps were contrasted to qualitative interpretation of perfusion color maps, respectively. By using the lesion maps to exclude lesions detected qualitatively on color maps, specificity improved (80 %). Point biserial correlation for computer-generated lesions (R _pb?=?0.46, p?<?0.0001) and lesions detected qualitatively (R _pb?=?0.32, p?=?0.0016) demonstrated positive correlation between size and infarction. Seventy-three percent (p?=?0.018) of lesions which demonstrated an increasing size from CBV, cerebral blood flow, to MTT/time to peak were true positive. Used in isolation, computer-generated lesion maps in CTP provide limited diagnostic utility in predicting infarct, due to their inherently low specificity. However, when used in conjunction with qualitative perfusion color map assessment, the lesion maps can help improve specificity.     

Correlation of volumetric mismatch and mismatch of Alberta Stroke Program Early CT Scores on CT perfusion maps

Introduction  We aimed to determine if volumetric mismatch between tissue at risk and tissue destined to infarct on computed tomography perfusion (CTP) can be described by the mismatch of Alberta Stroke Program Early CT Score (ASPECTS). Materials and methods  Forty patients with nonlacunar middle cerebral artery infarct <6 h old who had CTP on admission were retrospectively reviewed. Two raters segmented the lesion volume on mean transit time (MTT) and cerebral blood volume (CBV) maps using thresholds of >6 s and <2.0 mL per 100 g, respectively. Two other raters assigned ASPECTS to the same MTT and CBV maps while blinded to the volumetric data. Volumetric mismatch was deemed present if ≥20%. ASPECTS mismatch (=CBV ASPECTS − MTT ASPECTS) was deemed present if ≥1. Correlation between the two types of mismatches was assessed by Spearman’s coefficient (ρ). ROC curve analyses were performed to determine the optimal ASPECTS mismatch cut point for volumetric mismatch ≥20%, ≥50%, ≥100%, and ≥150%. Results  Median volumetric mismatch was 130% (range 10.9–2,031%) with 31 (77.5%) being ≥20%. Median ASPECTS mismatch was 2 (range 0–6) with 26 (65%) being ≥1. ASPECTS mismatch correlated strongly with volumetric mismatch with ρ = 0.763 [95% CI 0.585–0.870], p < 0.0001. Sensitivity and specificity for volumetric mismatch ≥20% was 83.9% [95% CI 65.5–93.5] and 100% [95% CI 65.9–100], respectively, using ASPECTS mismatch ≥1. Volumetric mismatch ≥50%, ≥100%, and ≥150% were optimally identified using ASPECTS mismatch ≥1, ≥2, and ≥2, respectively. Conclusion  On CTP, ASPECTS mismatch showed strong correlation to volumetric mismatch. ASPECTS mismatch ≥1 was the optimal cut point for volumetric mismatch ≥20%.     

Comparing two methods for assessment of perfusion-diffusion mismatch in a rodent model of ischaemic stroke: a pilot study

This stroke experiment was designed to define the mismatch between perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) in MRI by applying early or instantly acquired PWI. Eight rats were induced with stroke through photothrombotic occlusion of the middle cerebral artery and scanned serially between 1 h and day 3 after induction using DWI and PWI with a 1.5 T MR scanner. The relative lesion volumes (rLV) on MRI and triphenyl tetrazolium chloride-stained specimens were defined as the proportion of lesion volume over brain volume. Discrepancies in the rLV between PWI- and DWI-derived apparent diffusion coefficient (ADC) maps were expressed by subtraction of the ADC from PWI, resulting in three possible patterns: (i) (PWI-ADC > 10% of PWI) denoting a mismatch; (ii) (-(10% of PWI) 相似文献   

Reliability of MR perfusion-weighted and diffusion-weighted imaging mismatch measurement methods

BACKGROUND AND PURPOSE: We investigated 2 methods of measuring MR imaging perfusion-diffusion mismatch to determine whether reliability is improved by direct measurement on a single, blended map. MATERIALS AND METHODS: Image software was used for measurement of lesion volumes from diffusion-weighted images (DWI) and mean transit time (MTT) calculated from perfusion-weighted (PWI) images on 64 patients with acute stroke. For the first method, the DWI and MTT lesions were measured separately. For the second method, the mismatch volume was measured directly on the blended images created from the registered DWI and MTT images. RESULTS: Test-retest agreement was 100% and 97% for the separate and blended methods using mismatch cutoffs of 20% or more versus less than 20%. There were no significant differences in the mismatch statistics between the methods. CONCLUSIONS: Mismatch volumes by a single reader can provide highly reliable and consistent results even when separately measuring DWI and MTT lesions. Propagation of measurement error was not demonstrated, and the methods were statistically comparable.     

Perfusion-weighted magnetic resonance imaging of the brain: techniques and application in children

Perfusion-weighted magnetic resonance imaging (PWI) has been proposed as an attractive non-invasive tool for evaluating cerebral haemodynamics. Quantitative maps of cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), time to peak (TTP) and various other haemodynamic parameters can be obtained. Recent advances in hard- and software made PWI available for clinical routine. Although PWI became common in adult neuroradiology, it remains challenging in pediatric neuroradiology. In this article, the different PWI techniques that render haemodynamic maps of the brain are presented and discussed. The normal developmental changes of the cerebral haemodynamics in children as measured by PWI are presented as well as the application of PWI in cerebral ischaemia, primary and secondary cerebral vasculopathies and in cerebral tumours.     

兔脑缺血区扩散、灌注成像及细胞内钙的对照研究

目的　本实验预通过制作兔大脑中动脉持久性闭塞 (MCAo)模型 ,采用MR扩散和灌注加权成像 (DWI和PWI)确认半暗带 ,并与病理脑片水平不同缺血区域的细胞内钙离子浓度的变化进行对照研究 ,试图了解脑缺血早期半暗带MR特征及其与细胞内钙超载的关系。方法　 2 8只新西兰兔按MCAo后 0 5～ 3 6h间不同时间分为 7组 ,在既定时间行DWI及PWI,最后 1次MR检查完后立即处死动物 ,并迅速取脑 ,制作病理脑片及钙离子荧光探剂标记。将制备好的脑片置于激光共聚焦显微镜下观察兴趣区荧光强度。将缺血侧尾壳核区 (Ⅰ区 )、额顶叶皮质区 (Ⅱ区 )的MR各项参数及钙离子荧光强度进行配对t检验及方差分析。结果　MR结果显示MCAo后 ,缺血侧Ⅰ区、Ⅱ区脑血流量(CBF)、脑血容量 (CBV)较对侧有明显的降低 ,MCAo后 0 5～ 6h ,Ⅰ区的相对表观扩散系数 (rADC)明显低于Ⅱ区 (t=2 6 3 3 ,P <0 0 0 1)。 12h后差异无显著性意义 (F =1 60 ,P >0 0 5)。细胞内钙荧光检测结果显示MCAo后 0 5h ,Ⅰ区的荧光强度 (FI)即较对侧增强 3 18± 0 14倍 (t =5 2 7,P <0 0 5) ,而Ⅱ区与对侧相应区域在缺血后 1 5h以内FI差异无显著性意义 (F =3 2 1,P >0 0 5) ,3h后缺血侧Ⅱ区FI较对侧相应区域升高 (F =10 3 8,P <0 0 1)。Ⅰ区缺血 3h以内rA     

CT perfusion identifies increased salvage of tissue in patients receiving intravenous recombinant tissue plasminogen activator within 3 hours of stroke onset

BACKGROUND AND PURPOSE: In spite of the advent of thrombolytic therapy, CT-perfusion imaging is currently not fully used for clinical decision-making and not included in published clinical guidelines for management of ischemic stroke. We investigated whether lesion volumes on cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) maps predict final infarct volume and whether all these parameters are needed for triage to intravenous recombinant tissue plasminogen activator (rtPA). We also investigated the effect of intravenous rtPA on affected brain by measuring salvaged tissue volume in patients receiving intravenous rtPA and in controls.MATERIALS AND METHODS: Forty-four patients receiving intravenous rtPA and 19 controls underwent CT perfusion (CTP) studies in the emergency department within 3 hours of stroke onset. Lesion volumes were measured on MTT, CBV, and CBF maps by region-of-interest analysis and were compared with follow-up CT volumes by correlation and regression analysis. The volume of salvaged tissue was determined as the difference between the initial MTT and follow-up CT lesion volumes and was compared between intravenous rtPA-treated patients and controls.RESULTS: No significant difference between the groups was observed in lesion volume assessed from the CTP maps (P > .08). Coefficients of determination for MTT, CBF, and CBV versus follow-up CT lesion volumes were 0.3, 0.3, 0.47, with intravenous rtPA; and 0.53, 0.55, and 0.81 without intravenous rtPA. Regression of MTT on CBF lesion volumes showed codependence (R² = 0.98, P < .0001). Mean salvaged tissue volumes with intravenous rtPA were 21.8 ± 17.1 and 13.2 ± 13.5 mL in controls; these were significantly different by using nonparametric (P < .03) and Fisher exact tests (P < .04).CONCLUSIONS: Within 3 hours of stroke onset, CBV lesion volume does not necessarily represent dead tissue. MTT lesion volume alone can be used to identify the upper limit of the size of abnormally perfused brain. More brain is salvaged in patients with intravenous rtPA than in controls.

CT with physiologic imaging of cerebral perfusion (CTP) is routinely used at many centers around the world to assist in the triage of patients with acute stroke into various therapies, including intravenous thrombolysis with recombinant tissue plasminogen activator (rtPA). The use of CT in the triage process has been driven by the rapidity and wide availability of this imaging technique. Functional maps of cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) are readily constructed on a CT workstation and provide important information about the status of regional brain perfusion. Because giving intravenous rtPA is optimal within 3 hours of stroke ictus, it would be helpful to avoid spending time on those CTP parameters that do not provide critical information and to evaluate only those that directly impact the therapeutic decision.A key consideration in the assessment process of patients having acute stroke symptoms is how much affected brain tissue was already infarcted, how much is inevitably going to die, and how much could be potentially salvaged by therapy. It is this functional information that is being sought by using perfusion imaging and mapping of vascular physiology.^1-5 In the literature, it has been shown that lesion volumes on physiologic maps constructed from initial perfusion imaging in patients assessed in the 6- to 72-hour time window predict the final infarct volume.^6-9 Furthermore, several authors have shown that the volume of the initial CBV deficit approximates the final infarct size and likely represents already irreversibly infarcted tissue.^10,11Because the development of infarction is a dynamic time-dependent process, interpretation of the maps may well vary with the time from ictus. It was our aim in this study to investigate whether the lesion volumes observed on CBV, CBF, and MTT CTP maps, obtained within 3 hours of ictus, also predicted the final infarct volume and whether all these parameters are needed for triage. In addition, we investigated the effect of intravenous rtPA on affected brain tissue by measuring the final salvaged tissue volume in patients receiving intravenous rtPA and in a control group not receiving thrombolytic therapy.     

3D-ASL与DSC-PWI在缺血性脑梗死患者中的对比研究

目的：对比分析磁共振三维动脉自旋标记成像（3D-ASI。）与动态磁敏感对比增强灌注成像（DSC-PWI）在缺血性脑梗死患者中的临床应用价值。方法：32例缺血性脑梗死患者行常规MRI序列、DWI、MRA、3D-ASL及DSC-PWI检查。观察脑梗死患者的3D-ASI.DSC-PwI灌注后处理图像并进行评分（显示有低灌注记为-1,未见明显灌注异常记为0,高灌注记为＋1）,并比较分析ASI-CBF与PWI测量的CBF、CBV、MTT及TTP之间的差异。结果：32例中ASL显示灌注异常者有28（87．5％）例,PWI-CBF、PWI-CBV、PWI-MTT及PWI-TTP异常者分别为18（56．25％）、18（56．25％）、19（59．38％）和21（65．63％）例。McNemar检验结果显示,ASI。与PWI各参量图像所显示的灌注异常概率之间差异有统计学意义（P值分别为0．002、0．002、0．004和0．016）;除去在任意一种灌注图像上显示为高灌注的病例后,ASL-CBF与PWI各参量比较的P值分别为0．008、0．008、0．063和0．125,其中MTT及TTP的差异无统计学意义。结论：作为一种无创性MRI技术,ASL在临床应用中能够较为真实可靠地反映缺血性脑梗死的低灌注状态。     

Assessment of baseline hemodynamic parameters within infarct progression areas in acute stroke patients using perfusion-weighted MRI

Introduction

The value of perfusion MRI for identifying the tissue at risk has been questioned. Our objective was to assess baseline perfusion-weighted imaging parameters within infarct progression areas.

Methods

Patients with anterior circulation stroke without early reperfusion were included from a prospective MRI database. Sequential MRI examinations were performed on admission, 2?C3?h (H2), 2?C3?days (D2), and between 15 and 30?days after the initial MRI. Maps of baseline time-to-peak (TTP), mean transit time (MTT), cerebral blood volume (CBV), and cerebral blood flow (CBF) were calculated. Lesion extension areas were defined as pixels showing de novo lesions between each MRI and were generated by subtracting successive lesion masks: V₀, baseline diffusion-weighted imaging (DWI) lesion; V₁, lesion extension between baseline and H2 DWI; V₂, lesion extension from H2 to D2 DWI; and V₃, lesion extension from D2 DWI to final FLAIR. Repeated measures analysis was used to compare hemodynamic parameters within the baseline diffusion lesion and subsequent lesion extension areas.

Results

Thirty-two patients were included. Baseline perfusion parameters were significantly more impaired within the acute DWI lesion compared to lesion extension areas (TTP, p?p?p?p?p?=?0.01) and TTP (p?=?0.01) was found within successive lesion growth areas.

Conclusion

A decreasing gradient of severity for TTP and MTT was observed within successive infarct growth areas.     

急性脑缺血再灌注DWI及PWI的实验研究

目的:评价DWI及PWI判定急性脑梗死诊断及缺血半暗带的作用。材料和方法:40只SD大鼠随机均分4组,A组作假手术对照;B、D组分别栓塞2h、6h,均再灌注2h、24h;C组栓塞2h再灌注24h、7d。B、C、D组于各自栓塞及再灌注时间点行DWI、PWI及常规序列扫描;后处理获得表观扩散系数(ADC)、脑血容量(CBV)、脑血流量(CBF)、平均通过时间(MTT)形态图。并将结果与四氮唑红(TTC)染色和病理作比较。结果:A组DWI、PWI、TTC染色及病理观察均无异常;B、C、D组栓塞时均可见右大脑中动脉供血区DWI呈高信号,D组异常信号区面积明显大于B组,病理电镜表现为细胞内水肿。B、D组再灌注24hDWI异常信号区面积与灌注前相比,B组无明显变化,D组较前增大;C组再灌注7d6只大鼠DWI见高信号,但ADC图均正常。B、D组栓塞时右大脑中动脉供血区PWI灌注缺损区面积相似。B组PWI异常信号面积大于DWI异常信号区;D组PWI与DWI异常信号面积无明显差别。结论:DWI能灵敏反映急性期缺血脑组织损伤情况,PWI能灵敏反映组织血流灌注情况。DWI、PWI联合应用有可能判定缺血半暗带。     

Functional CT perfusion imaging in predicting the extent of cerebral infarction from a 3-hour middle cerebral arterial occlusion in a primate stroke model

BACKGROUND AND PURPOSE: Our purpose was to determine whether cerebral perfusion functional CT (fCT), performed after endovascular middle cerebral artery (MCA) occlusion, can be used to predict final cerebral infarction extent in a primate model. METHODS: fCT with bolus tracking was performed before and 30 and 150 minutes after 3-hour digital subtraction angiography (DSA)-guided endovascular MCA occlusion in five baboons. Parametric cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) maps were constructed by voxel-by-voxel gamma variate fitting and used to determine lesion sizes. Animals were sacrificed 48 hours after the occlusion, and ex vivo MR imaging was performed. Lesion sizes on fCT and MR images were compared. RESULTS: Hypoperfusion was clearly identified on all images obtained after MCA occlusion. Thirty and 150 minutes after occlusion onset, respectively, mean lesion sizes were 737 mm(2) +/- 33 and 737 mm(2) +/- 44 for CBF, 722 mm(2) +/- 32 and 730 mm(2) +/- 43 for CBV, and 819 mm(2) +/- 14 and 847 mm(2) +/- 11 for MTT. Mean outcome infarct size on MR images was 733 mm(2) +/- 30. Measurements based on CBV and CBF (R(2) = 0.97 and 0.96, P <.001), but not MTT (R(2) = 0.40, P >.5), were highly correlated with final lesion size. CONCLUSION: An endovascular approach to MCA occlusion provides a minimally invasive, reproducible animal model for controlled studies of cerebral ischemia and infarction. Derived cerebral perfusion maps closely predict the 48-hour infarct size after 3-hour MCA occlusion.     

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.     

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.     

MRI in acute subarachnoid haemorrhage; findings with a standardised stroke protocol

There is doubt as to whether acute haemorrhage is visible on MRI. We carried out MRI within 6 h of symptom onset on five patients with minor (low Hunt and Hess grades 1 or 2) subarachnoid haemorrhage (SAH) diagnosed by CT to search for any specific pattern. We used our standard stroke MRI protocol, including multiecho proton density (PD)- and T2-weighted images, echoplanar (EPI) diffusion- (DWI) and perfusion- (PWI) weighted imaging, and MRA. In all cases SAH was clearly visible on PD-weighted images with a short TE. In four patients it caused a low-signal rim on the T2*-weighted source images of PWI, and DWI revealed high signal in SAH. In the fifth patient SAH was perimesencephalic; susceptibility effects from the skull base made it impossible to detect SAH on EPI DWI and T2*-weighted images. Perfusion maps were normal in all cases. MRA and conventional angiography revealed an aneurysm in only one patient. Stroke MRI within 6 h of SAH thus shows a characteristic pattern.     

Use of ECG-gated single-photon emission tomography to assess the evolution of perfusion after acute myocardial infarction

Serial improvement in myocardial perfusion images from the acute or subacute to the chronic stage of acute myocardial infarction (AMI) has been attributed to improved coronary microcirculation or cell function after acute ischaemia and reperfusion. However, conventionally used non-gated imaging cannot eliminate the effect of improved regional contraction. We studied the possibility that such scintigraphic improvement reflects the functional recovery by using ECG-gated myocardial perfusion imaging with technetium-99m sestamibi. Nineteen AMI patients who received acute reperfusion therapy underwent ECG-gated myocardial single-photon emission tomography (SPET) in the subacute and chronic stages. Serial changes in regional image count distributions were analysed on the non-gated, end-diastolic (ED) and end-systolic (ES) images by using segmental mean percent peak activity (MPA) and ΔMPA (MPA in chronic stage – MPA in subacute stage) on bull’s-eye polar maps. These changes were compared with those in regional wall motion on biplane left ventriculography (LVG) from the acute (just after reperfusion) to the chronic stage. During the follow-up, regional wall motion remained the same in 42 (group A) but improved in 17 (group B) of the 59 ischaemically compromised segments. MPA showed no improvement in group A but significant improvement in group B on the non-gated and ES images (P<0.0001 and P<0.001, respectively). However, MPA on the ED images showed no improvement in either group. In the follow-up study of AMI, the scintigraphic improvement documented on the non-gated myocardial images appears to be mainly related to the recovery of wall thickening and not to a real improvement in myocardial perfusion. Therefore, ECG-gated myocardial imaging, which enables simultaneous assessment of changes in perfusion and contraction, is preferable to conventional non-gated imaging for follow-up of AMI. Received 26 October 1999 and in revised form 20 January 2000     

Time course of lesion development in patients with acute brain stem infarction and correlation with NIHSS score

BACKGROUND AND PURPOSE: diffusion weighted magnetic resonance imaging (MRI) is highly sensitive in detecting acute supratentorial cerebral ischemia and Diffusion Weighted Imaging (DWI) lesion size has been shown to correlate strongly with the neurologic deficit in middle cerebral artery territory stroke. However, data concerning infratentorial strokes are rare. We examined the size and evolution of acute brain stem ischemic lesions and their relationship to neurological outcome. METHODS: brain stem infarctions of 11 patients were analyzed. We performed DWI in all patients and in 7/11 patients within 24 h, T2W sequences within the first 2 weeks (10/11 patients) and follow-up MRI (MR2) within 3-9 months (median 4.8 months) later (12/12 patients). Lesion volumes were compared with early and follow-up neurologic deficit as determined by National Institutes of Health Stroke Scale (NIHSS) score. RESULTS: the relative infarct volumes--with MR2 lesion size set to 100%--decreased over the time (P<0.02) with a mean shrinking factor of 3.3 between DWI (MR0) and the follow-up MRT (P<0.02), and 1.6 between early T2W (MR1) and MR2 (P<0.04). The mean DWI volume size (MR0) was larger than the early T2W (P<0.02). Although neurological outcome was good in all patients (mean NIHSS score of 1.3 at follow-up), early NIHSS and follow-up NIHSS scores were strongly correlated (r=0.9, P<0.00). NIHSS score at follow-up was highly correlated with lesion size of DWI (MR0; r=0.71, P<0.04) and T2W of MR1 (r=0.86, P<0.001). CONCLUSIONS: in this study, we saw a shrinking of the brain stem infarct volume according to clinical improvement of patients. Great extension of restricted diffusion in the acute stage does not necessarily implicate a large resulting infarction or a bad clinical outcome.