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.     

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     

Reversed discrepancy between CT and diffusion-weighted MR imaging in acute ischemic stroke

PURPOSE: We sought to determine whether an early CT ischemic lesion showing parenchymal hypoattenuation might be undetectable on diffusion-weighted imaging (DWI) in acute cerebral ischemia. MATERIALS AND METHODS: We retrospectively evaluated CT and MR images of 70 consecutive patients with acute middle cerebral artery (MCA) infarction. All patients underwent CT and MR imaging within 6 hours of symptom onset. We determined the presence of reversed discrepancy (RD), defined as an early ischemic lesion showing parenchymal hypoattenuation on CT but no hyperintensity on DWI. CT Hounsfield units (HU), apparent diffusion coefficients (ADCs), and perfusion parameters were calculated for RD lesions. RESULTS: RD was found in 9 (12.9%) patients and at basal ganglia (89%). The mean HU of RD lesion was lower than that of normal tissue (DeltaHU, 2.33 +/- 0.74, P < .001). RD lesions showed no significant decrease of ADC (ADC ratio, 0.97 +/- 0.07, P = .059) and cerebral blood flow (relative CBF, 0.87 +/- 0.20, P > 0.05). Delayed DWI hyperintensity occurred in 8 (88.8%) RD lesions, and all lesions progressed to infarction. In 6 (66%) of 9 patients with RD, Alberto Stroke Program Early CT scores of ischemic lesions were lower on CT than those on DWI. CONCLUSION: RD was uncommonly found mainly in basal ganglia, and all RD lesions progressed to infarction at follow-up. Early CT ischemic lesion showing parenchymal hypoattenuation may be undetectable on DWI, and DWI may underestimate extent of severe ischemic tissue in patients with acute MCA infarction.     

Role of diffusion-weighted MR in differential diagnosis of intracranial cystic lesions

AIM: The purpose of this study was to evaluate the role of diffusion-weighted imaging (DWI) in characterizing cerebral cystic lesions. The usefulness of the apparent diffusion coefficient (ADC) map in lesion characterization was also evaluated. METHODS: We compared the findings of conventional MR images with those of DWI: 63 cystic masses in 48 patients were examined with routine MR imaging and echo-planar DWI. The routine MR imaging included at least the axial T2- and T1-weighted sequences, and post-contrast T1 axial sequences. The DWI included an echo-planar spin-echo sequence with three values (0, 500 and 1000s/mm(2)) sensitizing gradient in the x, y, z direction, and it obtained an ADC map. RESULTS: The sensitivity of DWI for differentiating abscesses from primary brain tumours was 100%; for differentiating abscesses from metastatic tumours was 73%; for differentiating benign from malignant lesions was 90%. CONCLUSION: Although some metastatic lesions may appear hyperintense on DWI thus imitating an abscess, evaluation of the lesions with both DWI and conventional MRI may have an important contribution to the differentiation of tumours from abscesses.     

磁共振DWI和PWI在超急性脑梗死诊治中的应用

目的评价磁共振弥散加权成像（DWI）和灌注加权成像（PWI）在超急性脑梗死诊断及指导临床早期溶栓治疗中的应用价值。方法 56例发病在6 h以内且临床提示处于超急性期脑梗死患者均行急诊MRI检查,扫描序列包括T1WI、T2WI、FLAIR、DWI及PWI,部分病例行MRA检查。结果 56例患者T1WI均未见异常信号,35例患者T2WI、FLAIR发现有轻微异常信号影。56例DWI和PWI均发现异常,但在DWI上显示的高信号急性脑梗死区域与在PWI上显示的脑灌注延长区域不匹配,PWI显示的病灶范围更大。图像后处理显示平均通过时间（MTT）、达峰时间（TTP）均有不同程度的延长,脑血流量（CBF）出现不同程度的减少。结论急诊MRI,特别是DWI和PWI序列对超急性脑梗死患者可以作出准确的诊断,可以安全、迅速、有效地指导临床进行早期溶栓治疗。     

软组织肿瘤MR扩散成像与灌注成像的比较研究

目的 通过分析一组软组织肿瘤同一病例相同ROI的MR DWI及PWI的影像信息,比较这2种MR功能成像技术用于软组织肿瘤的定性诊断价值.方法 对50例软组织肿瘤(良性24例,恶性26例)同时行DWI及PWI.通过扩散及灌注软件分析DWI及PWI参数在良、恶性肿瘤中的表现,进行差异的t检验,对所获两法的诊断符合率进行x2检验.采用受试者操作特征曲线(ROC曲线)分析曲线下面积(AUC),确定诊断阈值并对2种诊断方法进行评价.结果 良、恶性软组织肿瘤的ADC值[(良、恶性分别为(2.03±0.36)和(1.52±0.39)×10-3mm2/s]、首过灌注(FP)期信号强度丢失率[良、恶性分别为(13.54±3.37)%和(47.57±5.21)%]的差异均有统计学意义(t值分别为2.515和2.938,P值均<0.05),时间-信号强度曲线(TIC)最大线性斜率[良、恶性分别为(5.51±2.54)%和(7.94±3.33)%]的差异无统计学意义(t值为1.272,P>0.05);以ADC值1.866×10-3mm2/s为阈值,DWI诊断恶性肿瘤的敏感度为84.6%(22/26),特异度为83.3%(20/24);以FP期最大信号丢失率40.33%为阈值,PWI诊断恶性肿瘤的敏感度为88.5%(23/26),特异度为75.0%(18/24);TIC类型的Ⅰa型在良性肿瘤中占3/24,在恶性肿瘤中占20/26;Ⅰb型在良性肿瘤中占14/24,在恶性肿瘤中占3/26;Ⅰc型在恶性肿瘤中占3/26.Ⅱ型TIC在良性肿瘤中占7/24.在DWI上用ADC值、PWI上用FP期最大信号强度丢失率作诊断,诊断符合率分别为84.0%(42/50)和82.0%(41/50),两者的差异无统计学意义(x2=0.8,P>0.05);AUC测得的准确度分别为81.7%和83.6%,PWI诊断恶性软组织肿瘤的敏感度高.结论 以DWI和PWI的ADC值、FP期信号强度丢失率分别为1.866×10-3mm2/s和40.33%为阈值时,均有利于软组织肿瘤良、恶性的鉴别;TIC最大线性斜率对于软组织肿瘤良、恶性的鉴别意义不大;软组织肿瘤的TIC形态有助于肿瘤良、恶性的鉴别.DWI和PWI用于诊断恶性软组织肿瘤的准确性均为中等,在DWI与PWI用于诊断恶性软组织肿瘤的准确性相近时,应选择诊断敏感度较高的PWI.     

Assessment of diffusion and perfusion deficits in patients with small subcortical ischemia

BACKGROUND AND PURPOSE: Using perfusion- and diffusion-weighted MR imaging in acute ischemic stroke of the middle cerebral artery (MCA), previous studies have shown a typical pathophysiologic pattern that is characterized by a perfusion deficit larger than the diffusion lesion (mismatch), with the final lesion usually comprising the initial diffusion lesion (core) plus parts of the initial mismatch area. Little is known about underlying pathophysiology in small ischemic stroke. In this study, we used perfusion- and diffusion-weighted MR imaging to investigate the underlying pathophysiology of small subcortical ischemia. METHODS: Six consecutive patients (age range, 42-76 years) with small subcortical ischemia were examined by using a 1.5-T MR system 2-5, 22-55, and 144-392 hours after the onset of symptoms. T2-weighted, diffusion-weighted imaging at b=0 s/mm2 and b=1000 s/mm2, and bolus-track perfusion-weighted imaging were performed. Lesion sizes were determined on the basis of T2-weighted findings as well as those of apparent diffusion coefficient (ADC) maps and CBF. RESULTS: In every patient, the initial CBF lesion was smaller than the initial ADC lesion. Both the CBF lesion and the ADC lesion increased in size from first to second examination. In all instances, however, the CBF lesion remained smaller than the ADC lesion. The CBF lesion observed during the acute phase and the one seen on the following days were both smaller than the final T2 lesion. CONCLUSION: Our data suggest that in contrast to previous findings in MCA ischemia in small subcortical infarcts tissue damage may spread beyond the area of the initial perfusion disturbance. In light of the small number of patients, further studies will have to address the relevance of this observation.     

Evolution of apparent diffusion coefficient, diffusion-weighted, and T2-weighted signal intensity of acute stroke

BACKGROUND AND PURPOSE: Serial study of such MR parameters as diffusion-weighted imaging (DWI), apparent diffusion coefficient (ADC), ADC with fluid-attenuated inversion recovery (ADC(FLAIR)), and T2-weighted imaging may provide information on the pathophysiological mechanisms of acute ischemic stroke. Our goals were to establish the natural evolution of MR signal intensity characteristics of acute ischemic lesions and to assess the potential of using specific MR parameters to estimate lesion age. METHODS: Five serial echo-planar DWI studies with and without an inversion recovery pulse were performed in 27 patients with acute stroke. The following lesion characteristics were studied: 1) conventional ADC (ADC(CONV)); 2) ADC(FLAIR); 3) DWI signal intensity (SI(DWI)); 4) T2-weighted signal intensity (SI(T2)), and 5) FLAIR signal intensity (SI(FLAIR)). RESULTS: The lesion ADC(CONV) gradually increased from low values during the first week to pseudonormal during the second week to supranormal thereafter. The lesion ADC(FLAIR) showed the same pattern of evolution but with lower absolute values. A low ADC value indicated, with good sensitivity (88%) and specificity (90%), that a lesion was less than 10 days old. All signal intensities remained high throughout follow-up. SI(DWI) showed no significant change during the first week but decreased thereafter. SI(T2) initially increased, decreased slightly during week 2, and again increased after 14 days. SI(FLAIR) showed the same initial increase as the SI(T2) but remained relatively stable thereafter. CONCLUSION: Our findings further clarify the time course of stroke evolution on MR parameters and indicate that the ADC map may be useful for estimating lesion age. Application of an inversion recovery pulse results in lower, potentially more accurate, absolute ADC values.     

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.     

Perfusion and diffusion MR imaging in enhancing malignant cerebral tumors

OBJECTIVE: Common contrast-enhancing malignant tumors of the brain are glioblastoma multiforme (GBMs), anaplastic astrocytomas (AAs), metastases, and lymphomas, all of which have sometimes similar conventional MRI findings. Our aim was to evaluate the role of perfusion MR imaging (PWI) and diffusion-weighted imaging (DWI) in the differentiation of these contrast-enhancing malignant cerebral tumors. MATERIALS AND METHODS: Forty-eight patients with contrast-enhancing and histologically proven brain tumors, 14 AAs, 17 GBMs, nine metastases, and eight lymphomas, were included in the study. All patients have undergone routine MR examination where DWI and PWI were performed in the same session. DWI was performed with b values of 0, 500, and 1000 mm(2)/s. Minimum ADC values (ADC(min)) of each tumor was later calculated from ADC map images. PWI was applied using dynamic susceptibility contrast technique and maximum relative cerebral blood volume (rCBV(max)) was calculated from each tumor, given in ratio with contralateral normal white matter. Comparisons of ADC(min) and rCBV(max) values with the histological types of the enhancing tumors were made with a one-way analysis of variance and Bonferroni test. A P value less than 0.05 indicated a statistically significant difference. RESULTS: The ADC(min) values (mean+/-S.D.) in GBMs, AAs, lymphomas, and metastases were 0.79+/-0.21 (x10(-3)mm(2)/s), 0.75+/-0.21 (x10(-3)mm(2)/s), 0.51+/-0.09 (x10(-3)mm(2)/s), and 0.68+/-0.11 (x10(-3)mm(2)/s), respectively. The difference in ADC(min) values were statistically significant between lymphomas and GBMs (P<0.05). It was also statistically significant between lymphomas and AAs (P<0.03). However, there were no differences between lymphomas and metastasis, and between GBMs, AAs, and metastasis. The rCBV(max) ratio (mean+/-S.D.) in GBMs were 6.33+/-2.03, whereas it was 3.66+/-1.79 in AAs, 2.33+/-0.68 in lymphomas, and 4.45+/-1.87 in metastases. These values were statistically different between GBMs and AAs (P<0.001), GBMs and lymphoma (P<0.0001). Although there seemed to be difference between GBMs and metastases, it was not statistically significant (P<0.083). CONCLUSION: Combination of DWI and PWI, with ADC(min) and rCBV(max) calculations, may aid routine MR imaging in the differentiation of common cerebral contrast-enhancing malignant tumors.     

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。     

Feasibility of diffusion-weighted imaging in the differentiation of metastatic from nonmetastatic lymph nodes: early experience

PURPOSE: To investigate the feasibility of diffusion-weighted imaging (DWI) in the differentiation of metastatic from nonmetastatic lymph nodes. MATERIALS AND METHODS: In 125 patients who underwent lymph node dissection for uterine cervical cancer, DWI was performed at b value of 0 and 1000 s/mm2. By referring to the surgical maps of the pelvic lymph nodes, the apparent diffusion coefficient (ADC) was compared in the metastatic and nonmetastatic lymph nodes, and receiver-operating-characteristics analysis was performed to evaluate the diagnostic performance of the ADC in differentiating metastatic from nonmetastatic lymph nodes. RESULTS: The ADC were significantly lower in the metastatic lymph nodes (0.7651x10(-3) mm2/s+/-0.1137) than in the nonmetastatic lymph nodes (1.0021x10(-3) mm2/s+/-0.1859; P<0.001). The area-under-the-curve of ADC for differentiating metastatic from nonmetastatic lymph nodes, was 0.902. The sensitivity and specificity of ADC for differentiating metastatic from nonmetastatic lymph nodes, were 87% for the ADC and 80%, respectively. CONCLUSION: DWI is feasible for differentiating metastatic from nonmetastatic lymph nodes in patients with uterine cervical cancer.     

急性期脑内血肿3.0T MR扩散加权成像表现

目的:探讨3.0T MR设备中平面回波扩散加权成像(EPI-DWI)和表观扩散系数(ADC)图对急性脑内血肿的诊断价值及与脑梗死的鉴别诊断能力。方法:对18例急性期脑内血肿患者行EPI-DWI检查,获得ADC图并与CT及常规MRI进行对比。同期选择发病时间、病变体积相近的急性脑梗死患者18例,比较急性期脑内血肿与脑梗死的MRI表现。结果:所有急性期脑内血肿在EPI-DWI及ADC图上均为混杂信号,尤其是较大血肿;不同大小血肿周边均可见低信号环。所有急性脑梗死病变均未见周边环状低信号。结论:血肿周边低信号环为急性期脑内血肿的特异性DWI表现,可资与急性脑梗死相鉴别。     

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   

CT sign of brain swelling without concomitant parenchymal hypoattenuation: comparison with diffusion- and perfusion-weighted MR imaging

PURPOSE: To retrospectively evaluate the apparent diffusion coefficient (ADC) on magnetic resonance (MR) images and the perfusion parameters of lesions that show brain swelling without concomitant parenchymal hypoattenuation on computed tomographic (CT) scans. MATERIALS AND METHODS: Review board approval was obtained, and informed consent was waived. A total of 14 patients (seven men and seven women; mean age, 64 years +/- 11) were retrospectively selected from the consecutive 172 patients with acute cerebral ischemia who underwent CT within 6 hours of symptom onset. All patients had brain swelling without parenchymal hypoattenuation, including loss of gray-white matter distinction on CT scans, and they underwent diffusion- and perfusion-weighted MR imaging shortly after CT. CT attenuation, ADC, and perfusion parameters of relative cerebral blood volume (CBV), time to peak (TTP), and relative cerebral blood flow (CBF) were calculated for gray and white matter of the lesion. The measured values were compared with those of the contralateral hemisphere by using the paired t test; comparison of values of perfusion parameters among three subgroups was performed with the Kruskal-Wallis test. Arterial occlusions were determined with MR angiography or conventional angiography. RESULTS: The mean interval between initial CT and MR imaging was 2.4 hours +/- 0.9 (range, 0.4-3.4 hours). The ADC of lesions was similar to that of contralateral normal tissue (mean ADC ratio for gray matter and white matter, 0.99 and 0.97, respectively) (P > .05). Lesions had an increased relative CBV (P < .001), a mild to moderate TTP delay (P < .001), and a variable but not statistically significant reduction of relative CBF. The mean relative CBF of gray matter was less in patients who had complete infarction (0.81 +/- 0.16) than that in patients with partial infarction (0.99 +/- 0.16) or those with a normal radiologic outcome (1.12 +/- 0.22), but this difference was not statistically significant (P > .05). Proximal cerebral artery occlusions were found in all patients. In five (36%) patients, the lesion did not progress to infarction at follow-up. CONCLUSION: The CT sign of brain swelling without concomitant parenchymal hypoattenuation in patients with acute cerebral ischemia does not represent severe ischemic damage and may suggest ischemic penumbral or oligemic tissue.     

Diffusion-weighted MR imaging of neuro-Behçet's disease: a case report

We present a serial study of diffusion-weighted imaging (DWI) in a patient with neuro-Behçet's disease. Initial T2-weighted magnetic resonance images showed a hyperintense lesion in the brain stem. The lesion was slightly hyperintense on DWI and the apparent diffusion coefficient (ADC) was slightly increased. Ten months later, DWI showed an improvement in the abnormal signal intensity and the region of increased ADC had increased in size, especially on the left side. DWI is useful for differentiating an acute exacerbation of neuro-Behçet's disease from acute infarction.     

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.     

Cerebral abscesses and necrotic cerebral tumours: differential diagnosis by perfusion-weighted magnetic resonance imaging

PURPOSE: This study was undertaken to evaluate the usefulness of perfusion-weighted imaging (PWI) in the differential diagnosis of ring-enhancing cerebral lesions, including abscesses, high-grade gliomas and metastases. MATERIALS AND METHODS: Nine cerebral abscesses (five pyogenic, four from Toxoplasma gondii), ten glioblastomas and five cerebral metastases in 19 patients were studied with gadolinium-enhanced magnetic resonance imaging, diffusion-weighted imaging (DWI) including calculation of mean apparent diffusion coefficient (ADC) of the lesion core, and PWI. At PWI, the mean of the maximum regional cerebral blood volume (rCBV) was calculated in the gadolinium-enhancing peripheral solid areas and compared with that of the contralateral normal-appearing white matter [ratio=rCBV (lesion)/rCBV (contralateral normal-appearing white matter)]. RESULTS: DWI achieved the differential diagnosis in all cases except for the four Toxoplasma abscesses. At PWI, the mean ratio of the rCBV of the capsular portion was 0.72+/-0.08 (range 0.60-0.82) in the pyogenic abscesses, 0.84+/-0.07 (range 0.75-0.91) in the Toxoplasma abscesses, 4.45+/-1.5 (range 2.9-8.0) in the high-grade gliomas and 3.58+/-0.68 (range 3.28-4.27) in the metastases. CONCLUSIONS: PWI seems to be useful in the differential diagnosis of ring-enhancing cerebral lesions. High rCBV values in the peripheral areas appear to indicate the possibility of a necrotic tumour, whereas low values tend to indicate an abscess.     

Automatic prediction of infarct growth in acute ischemic stroke from MR apparent diffusion coefficient maps

RATIONALE AND OBJECTIVES: We introduce a new approach to the prediction of final infarct growth in human acute ischemic stroke based on image analysis of the apparent diffusion coefficient (ADC) maps obtained from magnetic resonance imaging. Evidence from multiple previous studies indicate that ADC maps are likely to reveal brain regions belonging to the ischemic penumbra, that is, areas that may be at risk of infarction in the few hours following stroke onset. MATERIALS AND METHODS: In a context where "time is brain," and contrarily to the alternative-and still-debated-perfusion-diffusion weighted image (PWI/DWI) mismatch approach, the DWI magnetic resonance sequences are standardized, fast to acquire, and do not necessitate injection of a contrast agent. The image analysis approach presented here consists of the segmentation of the ischemic penumbra using a fast three-dimensional region-growing technique that mimics the growth of the infarct lesion during acute stroke. RESULTS: The method was evaluated with both numerical simulations and on two groups of 20 ischemic stroke patients (40 patients total). The first group of patient data was used to adjust the parameters of the model ruling the region-growing procedure. The second group of patient data was dedicated to evaluation purposes only, with no subsequent adjustment of the free parameters of the image-analysis procedure. Results indicate that the predicted final infarct volumes are significantly correlated with the true final lesion volumes as revealed by follow-up measurements from DWI sequences. CONCLUSION: The DWI-ADC mismatch method is an encouraging fast alternative to the PWI-DWI mismatch approach to evaluate the likeliness of infarct growth during the acute stage of ischemic stroke.     

MR扩散加权成像对桥小脑角区实性神经鞘瘤与脑膜瘤的鉴别诊断价值

目的：探讨 MR扩散加权成像(DWI)及表观扩散系数(ADC)在桥小脑角区实性神经鞘瘤与脑膜瘤鉴别诊断中的价值。方法回顾性分析经术后病理证实的桥小脑角区12例实性神经鞘瘤和27例脑膜瘤的 DWI 图像,逐层勾画肿瘤边界以获得整体感兴趣区(ROI),得到肿瘤的平均 ADC 值(mADC)。同时以脑干 mADC 值为参考,计算得到肿瘤/脑干 ADC 比值(ADC ratio, rADC=肿瘤 mADC值/脑干 mADC值)。桥小脑角区实性神经鞘瘤和脑膜瘤之间的 mADC 和 rADC 值差异采用独立样本t检验分析。采用受试者工作特征曲线(ROC)分析 mADC 和 rADC 值在两者鉴别诊断中的价值。结果桥小脑角区实性神经鞘瘤mADC和 rADC值均明显高于脑膜瘤(mADC,P=0.001;rADC,P=0.002)。以 mADC=0.994×10-3 mm2/s 作为诊断阈值,鉴别实性神经鞘瘤和脑膜瘤的价值最优[曲线下面积(AUC)0.917;敏感度92%;特异度89%]。结论 MR DWI对桥小脑角区实性神经鞘瘤与脑膜瘤的鉴别诊断有一定的参考价值。