Combined perfusion- and diffusion-weighted MR imaging in acute ischemic stroke during the 1st week: a longitudinal study

PURPOSE: To compare findings with different magnetic resonance (MR) perfusion maps in acute ischemic stroke. MATERIALS AND METHODS: Combined diffusion-weighted (DW) and perfusion-weighted (PW) MR imaging was performed in 49 patients with acute (<24 hours) stroke, on the 1st and 2nd days and 1 week after stroke. Volumes of hypoperfused tissue on maps of relative cerebral blood volume (rCBV), relative cerebral blood flow (rCBF), and mean transit time (MTT) were compared with the volume of infarcted tissue at DW imaging. RESULTS: The mean infarct volume increased from 41 to 65 cm(3) between the 1st and 2nd days (P: <.001; n = 49). On the 1st day, all perfusion maps on average showed hypoperfusion lesions larger than the infarct at DW imaging (P: <.001; n = 49). MTT maps showed significantly (P: <.001) larger hypoperfusion lesions than did rCBF maps, which showed significantly (P: <.001) larger hypoperfusion lesions than did rCBV maps. The sizes of the initial perfusion-diffusion mismatches correlated significantly with the extent of infarct growth (0.479 < r < 0.657; P: 相似文献   

脑梗死前期脑局部微循环障碍CT灌注成像的实验研究

目的 从微循环的角度探讨脑梗死前期CT灌注成像表现及其病理基础，以及星形细胞与脑局部微循环的关系。方法 建立大鼠脑局部低灌注模型和脑局部星形细胞水肿模型，在动态CT脑灌注成像检查后处死，分别作灌注CT参数图、红四氮唑(TTC)染色、电子显微镜(简称电镜)和光学显微镜(简称光镜)观察。脑局部低灌注模型作了局部脑血流量(regional cerebral blood flow，rCBF)、局部脑血容量(regional cerebral blood volume，rCBV)、平均通过时间(mean transit time，MTT)和最大峰值时间(time-to-peak，TTP)比值(病侧／健侧)测量。结果 大鼠脑局部低灌注模型实验组的rCBF和MTT参数图显示病变侧低灌注区，rCBV和TTP参数图未见异常。rCBF、rCBV、MTT和TTP的比值范围分别为：0．39～0．55、0．92～1．00、1．20～1．50和1．00～1．00。电镜见星形细胞水肿，肿胀的星形细胞足板挤压毛细血管使管腔狭窄或闭塞；神经元表现正常或有轻度可逆损伤。假手术组各个参数图、TTC染色、电镜以及光镜未见异常。大鼠脑局部星形细胞水肿模型实验组4只大鼠的rCBF和MTT参数图均见星形细胞水肿所造成的局部低灌注带和局部MTT延长区域，其中3只rCBV参数图显示异常低灌注区，2只TTP参数图显示TTP异常延长区域。rCBF、rCBV、MTT和TTP的比值范围分别为：0．25～0．44、0．70～1．01、1．20～2．00和1．02～1．45。电镜观察到星形细胞水肿，足板不同程度的肿胀，极度肿胀的星形细胞足板挤压毛细血管使管腔狭窄或闭塞；神经元基本正常或仅有核膜凹陷。对照组的CT灌注成像、TTC染色、电镜和光镜均未见异常。结论 rCBF下降到电衰竭阈值和膜衰竭阈值之间时，星形细胞可以作出比神经元更为迅速的反应，即星形细胞水肿。星形细胞足板肿胀使得毛细血管的管腔变窄，造成局部微循环障碍，加重脑局部的缺血缺氧。动态CT脑灌注成像可清楚地显示上述状态下异常血液动力学变化，rCBF与rCBV之间的变化关系可提示脑缺血区微循环障碍的程度。     

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.     

脑出血亚急性及慢性期血肿周围组织低灌注损伤的CT灌注成像研究

目的 探讨脑出血亚急性及慢性期血肿周围组织脑血液动力学变化及其相关影响因素。方法 对12例基底节区脑出血患者做了CT常规及灌注成像检查，对其中11例患者血肿体积及血肿周围局部脑血流量（regional cerebral blood flow，rCBF）、局部脑血容量（regional cerebral blood volume，rCBV）、对比剂平均通过时间（mean transit time，MTT）和最大峰值时间（time-to-peak，TTP）的比值（病侧／健侧）进行测量。结果 11例脑出血患者血肿体积最大为72．21ml，最小为13．68ml，血肿平均体积为26．83ml。rCBF参数图显示血肿周围低灌注梯度11例，表现为血肿周围rCBF减低区；rCBV参数图显示血肿周围低灌注梯度10例，表现为血肿周围rCBV减低区；血肿周围高灌注1例，表现为血肿周围rCBV增高区；同侧半球低灌注2例，表现为血肿侧脑组织rCBF、rCBV大面积减低区；时间参数图显示血肿周围TTP延长11例，MTT延长10例；血肿边缘区rCBF显著低于外层区rCBF；边缘区MTT、TTP明显长于外层区MTT、TTP；血肿外层区rCBF、rCBV与血肿边缘区rCBF、rCBV呈线性依从性改变。血肿周围（边缘区和外层区）rCBV与血肿体积有明显的相关性，r边缘区=0．764，r外层区=0．703（双侧），P值均〈0．05。血肿周围rCBF、rCBV、MTT和TTP与症状出现至行CT灌注扫描间期无明显相关性。结论 脑出血亚急性和慢性期，血肿周围脑组织依然存在低灌注梯度，低灌注区脑血流变化与血肿体积密切相关。CT灌注成像可清晰地显示出血肿周围异常的脑血液动力学变化，可为脑出血个体化救治及预后评估提供有价值的信息。     

Perfusion CT in acute stroke: predictive value of perfusion parameters in assessing tissue viability versus infarction

PURPOSE: The aim of this study was to assess the value of computed tomography (CT) perfusion parameters in differentiating tissue viability in acute stoke patients. MATERIALS AND METHODS: Thirteen patients (mean age 63.3 years) with nonhaemorrhagic stroke underwent multidetector perfusion CT within 3 h of symptom onset. Images were continuously acquired at the basal ganglia over 40 s during injection of 90 ml of iodinated contrast medium injected at a rate of 9 ml/s with a 9-s delay. Z-axis coverage was 20 mm. All patients underwent diffusion-weighted magnetic resonance imaging (DWI) within 12 h of perfusion CT to define the extent of the infarct. Perfusion CT data were analysed in regions of interests (ROIs) on regional cerebral blood volume (rCBV), regional cerebral blood flow (rCBF) and mean transit time (MTT) maps placed in various parts of the perfusion-deficient territory and in the contralateral hemisphere. Statistical analysis was performed using the analysis of variance (ANOVA) test to assess differences in CT perfusion parameters. Receiver operator characteristics (ROC) analysis was performed to assess possible threshold values that predict tissue infarction vs. viability. RESULTS: Normal CT findings with abnormal CT perfusion parameters were seen in the region of infarction and in the viable tissue (penumbra) within a 1.5-cm distance from the infarct margin as outlined on DWI images. Infarcted areas demonstrated significant prolongation of MTT values compared with noninfarcted areas (p<0.0001). Average MTT was 9.8 s in areas of infarction, 5.1 s in the viable tissue adjacent to the infarct (penumbra), and 3.4 s in the contralateral control area. An MTT threshold level of 6.05 s has a 100% positive predictive value (sensitivity 84.6%, specificity 100%, accuracy 92.3%) for the presence of infarcted tissue. Average rCBF was 24.6 ml/100 g per min in infarcted tissue, 64.8 in penumbra and 70.8 in normal tissue. Average rCBV was 3.5 ml/100g in infarcted tissue, 3.9 in penumbra and 2.9 in normal tissue. CONCLUSIONS: Prolongation of MTT was the most frequent CT perfusion finding observed in acute stroke patients. Average MTT values of 5.1 s may distinguish viable tissue, whereas MTT values >6.05 s identify infarcted tissue.     

High-grade and low-grade gliomas: differentiation by using perfusion MR imaging

AIM: Relative cerebral blood volume (rCBV) is a commonly used perfusion magnetic resonance imaging (MRI) technique for the evaluation of tumour grade. Relative cerebral blood flow (rCBF) has been less studied. The goal of our study was to determine the usefulness of these parameters in evaluating the histopathological grade of the cerebral gliomas. METHODS: This study involved 33 patients (22 high-grade and 11 low-grade glioma cases). MRI was performed for all tumours by using a first-passage gadopentetate dimeglumine T2*-weighted gradient-echo single-shot echo-planar sequence followed by conventional MRI. The rCBV and rCBF were calculated by deconvolution of an arterial input function. The rCBV and rCBF ratios of the lesions were obtained by dividing the values obtained from the normal white matter of the contralateral hemisphere. For statistical analysis Mann-Whitney testing was carried out. A p value of less than 0.05 indicated a statistically significant difference. Receiver operating characteristic curve (ROC) analysis was performed to assess the relationship between the rCBV and rCBF ratios and grade of gliomas. Their cut-off value permitting discrimination was calculated. The correlation between rCBV and CBF ratios and glioma grade was assessed using Pearson correlation analysis. RESULTS: In high-grade gliomas, rCBV and rCBF ratios were measured as 6.50+/-4.29 and 3.32+/-1.87 (mean+/-SD), respectively. In low-grade gliomas, rCBV and rCBF ratios were 1.69+/-0.51 and 1.16+/-0.38, respectively. The rCBV and rCBF ratios for high-grade gliomas were statistically different from those of low-grade gliomas (p < 0.001). The rCBV and CBF ratios were significantly matched with respect to grade, but difference between the two areas was not significant (ROC analysis, p > 0.05). The cut-off value was taken as 1.98 in the rCBV ratio and 1.25 in the rCBF ratio. There was a strong correlation between the rCBV and CBF ratios (Pearson correlation = 0.830, p < 0.05). CONCLUSION: Perfusion MRI is useful in the preoperative assessment of the histopathologicalal grade of gliomas; the rCBF ratio in addition to the rCBV ratio can be incorporated in MR perfusion analysis for the evaluation.     

FAIR and dynamic susceptibility contrast-enhanced perfusion imaging in healthy subjects and stroke patients

PURPOSE: To compare dynamic susceptibility contrast-enhanced magnetic resonance imaging (DSC-MRI) and the flow-sensitive alternating inversion recovery (FAIR) technique for measuring brain perfusion. MATERIALS AND METHODS: We investigated 12 patients with acute stroke, and 10 healthy volunteers with FAIR and DSC maps of regional cerebral blood volume (rCBV), mean transit time (MTT), and regional cerebral blood flow (rCBF). RESULTS: In volunteers good gray/white-matter contrast was observed in FAIR, rCBF, and rCBV maps. Regions with high signal intensities in FAIR matched well with high values of rCBV and rCBF. In ischemic stroke patients a high correlation (r = 0.78) of the ipsi- to contralateral signal intensity ratios in FAIR and rCBF was observed in areas with perfusion abnormalities. In contrast, FAIR and rCBV (r = 0.50), and FAIR and MTT (r = -0.22) correlated only modestly. Furthermore, FAIR and rCBF demonstrated similar sizes of perfusion abnormality. CONCLUSION: This study demonstrates for the first time that FAIR and rCBF depict similar relations of perfusion in ischemic stroke patients and healthy subjects.     

Quantitative assessment of the time course of infarct signal intensity on diffusion-weighted images

BACKGROUND AND PURPOSE: Diffusion-weighted (DW) MR imaging is important in evaluating acute stroke, and knowledge of the signal intensity changes associated with acute stroke is valuable. Our purpose was to model the time course of the signal intensity of infarcts and to characterize the apparent diffusion coefficient (ADC) and T2 effects on total signal intensity. METHODS: Ninety-two patients were included in this prospective cross-sectional study. Signal intensity in infarcts (4 hours to 417 days) and control regions were recorded on DW images (b = 0 and 1000 s/mm(2)), ADC maps, and ratio images (image with b = 1000 s/mm(2) divided by image with b = 0 s/mm(2)). Cubic spline functions were used for polynomial fitting. The time courses of log signal intensity with log time were modeled. The independent contributions of T2 and ADC to the total signal intensity were retrospectively compared at 0-63 hours, 3-10 days, 11-57 days, and 57 days onward. RESULTS: Mean signal intensity on DW images was maximal at 40 hours after infarction and normalized at 57 days. At 0-63 hours, the positive effect of ADC on signal intensity was greater than that of T2 (log value,13 +/- 0.04 vs 0.11 +/- 0.05; P =.04). At days 3-10, the positive T2 effect predominated (0.13 +/- 0.08 vs 0.08 +/- 0.04; P =.12). At 10-57 days, the positive T2 effect was greater than the negative ADC effect. After day 57, the negative ADC effect predominated. CONCLUSION: The signal intensity of infarcts on DW images normalizes at 57 days, which is substantially later than previously suggested. T2 (shine-through) effect contributes largely to the total infarct signal intensity.     

CT perfusion parameter values in regions of diffusion abnormalities

BACKGROUND AND PURPOSE: Dynamic CT perfusion imaging is a rapid and widely available method for assessing cerebral hemodynamics in the setting of ischemia. Nevertheless, little is known about perfusion parameters within regions of diffusion abnormality. Since MR diffusion-weighted (DW) imaging is widely considered the most sensitive and specific technique to examine the ischemic core, new knowledge about CT perfusion findings in areas of abnormal diffusion would likely provide valuable information. The purpose of our study was to measure the CT-derived perfusion values within acute ischemic lesions characterized by 1) increased signal intensity on DW images and 2) decreased apparent diffusion coefficient (ADC) and compare these values with those measured in contralateral, normal brain tissue. METHODS: Analysis was performed in 10 patients with acute middle cerebral artery territory stroke of symptom onset less than 8 hours before imaging who had undergone both CT perfusion and DW imaging within 2 hours. After registration of CT perfusion and DW images, measurements were made on a pixel-by-pixel basis in regions of abnormal hyperintensity on DW images and in areas of decreased ADC. RESULTS: Significant decreases in cerebral blood flow and cerebral blood volume with elevated mean transit times were observed in regions of infarct as defined by increased signal intensity on DW images and decreased ADC. Comparison of perfusion parameters in regions of core infarct differed significantly from those measured in contralateral normal brain. CONCLUSION: CT perfusion findings of decreased cerebral blood flow, mean transit time, and cerebrovascular volume correlate with areas of abnormal hyperintensity on DW images and regions of decreased ADC. These findings provide important information about perfusion changes in acute ischemia in areas of diffusion abnormality.     

Change of diffusion anisotropy in patients with acute cerebral infarction using statistical parametric analysis

Purpose We conducted statistical parametric comparison of fractional anisotropy (FA) images and quantified FA values to determine whether significant change occurs in the ischemic region. Materials and methods The subjects were 20 patients seen within 24 h after onset of ischemia. For statistical comparison of FA images, a sample FA image was coordinated by the Talairach template, and each FA map was normalized. Statistical comparison was conducted using SPM99. Regions of interest were set in the same region on apparent diffusion coefficient (ADC) and FA maps, the region being consistent with the hyperintense region on diffusion-weighted images (DWIs). The contralateral region was also measured to obtain asymmetry ratios of ADC and FA. Results Regions with areas of statistical significance on FA images were found only in the white matter of three patients, although the regions were smaller than hyperintense regions on DWIs. The mean ADC and FA ratios were 0.64 ± 0.16 and 0.93 ± 0.09, respectively, and the degree of FA change was less than that of the ADC change. Significant change in diffusion anisotropy was limited to the severely infarcted core of the white matter. Conclusion We believe statistical comparison of FA maps to be useful for detecting different regions of diffusion anisotropy. This article was presented at a Japan Radiological Society meeting in April 2005     

MR灌注成像在鉴别胶质瘤复发与放射性脑损伤中的价值

目的 分析MR灌注成像在鉴别胶质瘤复发与放射性脑损伤中的作用.方法 选取15例脑胶质瘤术后、放疗后并出现新强化灶的患者.所有患者均经二次手术病理或随访(随访时间＞6个月)证实为胶质瘤复发或放射性脑损伤.15例患者均行常规MR平扫、增强扫描和MR脑灌注成像.灌注成像采用梯度回波-回波平面成像(GRE-EPI)序列,ROI放置在横断面T1WI异常强化区域和对侧相对正常的脑白质内,大小为20～40 mm2,每个病灶测量10～15次,取平均值,计算异常强化区与对侧正常区的参数比值,包括相对脑血容量(rCBV)、相对脑血流量(rCBF)及相对平均通过时间(rMTT),采用秩和检验比较胶质瘤复发和放射性脑损伤各灌注参数.并采用ROC曲线评价rCBV、rCBF及MTT鉴别诊断两者的灵敏度及特异度.结果 15例患者最终经手术和随访证实有9例胶质瘤复发,6例放射性脑损伤.胶质瘤复发rCBV、rCBF比值的M分别为2.87(范围0.70～4.91)、1.89(范围0.64～3.96),明显高于放射性脑损伤比值[rCBV 0.70(范围0.12～1.62)、rCBF 0.56(范围0.12～2.08)],差异有统计学意义(Z值分别为-2.55、-2.08,P值均＜0.05).rCBV和rCBF比值鉴别诊断为胶质瘤复发或放射性脑损伤的ROC曲线下面积为0.893和0.821.rCBV比值≤0.77时诊断放射性脑损伤灵敏度为100.0%,rCBV比值≥2.44时诊断胶质瘤复发特异度为100.0%.结论 MR灌注成像是鉴别胶质瘤复发和放射性脑损伤的有效方法,rCBV比值和rCBF比值在鉴别诊断中具有重要价值.

Abstract：

Objective To evaluate the feasibility of perfusion weighted imaging (PWI) in the differentiation of recurrent glioma and radiation-induced brain injuries. Methods Fifteen patients with previously resected and irradiated glioma, presenting newly developed abnormal enhancement, were included in the study. The final diagnosis was determined either histologically or clinicoradiologically. PWI was obtained with a gradient echo echo-planar-imaging (GRE-EPI) sequence. The normalized rCBV ratio[CBV(abnormal enhancement)/CBV(contralateral tissue)], rCBF ratio[CBF(abnormal enhancement)/CBF(contralateral tissue)]and rMTT ratio[(MTT abnormal enhancement)/MTT(contralateral tissue)]were calculated, respectively. The regions of interest (ROIs) consisting of 20-40 mm2 were placed in the abnormal enhanced areas on postcontrast T1-weighted images. Ten to fifteen ROIs measurements were performed in each lesion and the mean value was obtained. Mann-Whitney test was used to determine whether there was a difference in the rCBV/rCBF/MTT ratios between glioma recurrence and radiated injuries. Results Nine of the 15 patients were proved recurrent glioma,6 were proved radiation-induced brain injuries. The mean rCBV ratio[2.87(0.70-4.91)]in glioma recurrence was markedly higher than that[0.70(0.12-1.62)]in radiation injuries (Z=-2.55,P＜0.05). The mean rCBF ratio[1.89(0.64-3.96)]in glioma recurrence was markedly higher than that[0.56(0.12-2.08)]in radiation injuries (Z=-2.08,P＜0.05). The areas under rCBV and rCBF ROC curve were 0.893 and 0.821. If the rCBV ratio ≤0.77, the diagnosis sensitivity of radiation-induced brain injuries was 100.0%;If ≥2.44, the diagnosis specificity of recurrent glioma was 100.0%. Conclusion PWI was an effective technique in distinguishing glioma recurrence from radiation injuries and rCBV and rCBF ratios were of great value in the differentiation.     

Pituitary macroadenomas: preoperative evaluation of consistency with diffusion-weighted MR imaging--initial experience

PURPOSE: To prospectively evaluate use of diffusion-weighted (DW) magnetic resonance (MR) images and apparent diffusion coefficient (ADC) maps for determination of the consistency of macroadenomas. MATERIALS AND METHODS: The study protocol was approved by the institutional ethics committee, and informed consent was obtained from all patients. Twenty-two patients with pituitary macroadenoma (10 men, 12 women; mean age, 54 years +/- 17.09 [standard deviation]; range, 21-75 years) were examined. All patients underwent MR examination, which included T1-weighted spin-echo and T2-weighted turbo spin-echo DW imaging with ADC mapping and contrast material-enhanced T1-weighted spin-echo imaging. Regions of interest (ROIs) were drawn in the macroadenomas and in normal white matter on DW images, ADC maps, and conventional MR images. Consistency of macroadenomas was evaluated at surgery and was classified as soft, intermediate, or hard. Histologic examination was performed on surgical specimens of macroadenomas. Mean ADC values, signal intensity (SI) ratios of tumor to white matter within ROIs on conventional and DW MR images, and degree of enhancement were compared with tumor consistency and with percentage of collagen content at histologic examination by using analysis of variance for linear trend. RESULTS: The mean value of ADC in the soft group was (0.663 +/- 0.109) x 10(-3) mm(2)/sec; in the intermediate group, (0.842 +/- 0.081) x 10(-3) mm(2)/sec; and in the hard group, (1.363 +/- 0.259) x 10(-3) mm(2)/sec. Statistical analysis revealed a significant correlation between tumor consistency and ADC values, DW image SI ratios, T2-weighted image SI ratios, and percentage of collagen content (P < .001, analysis of variance). No other statistically significant correlations were found. CONCLUSION: Findings in this study suggest that DW MR images with ADC maps can provide information about the consistency of macroadenomas.     

Brain abscess and cystic brain tumor: discrimination with dynamic susceptibility contrast perfusion-weighted MRI

Differentiating between brain abscesses and cystic brain tumors such as high-grade gliomas and metastases is often difficult with conventional MRI. The goal of this study was to evaluate the diagnostic utility of perfusion MRI to differentiate between these pathologies. MRI was performed in 19 patients with rim-enhancing brain lesions (4 pyogenic abscesses, 8 high-grade gliomas, 7 metastases). In addition to standard MR sequences, trace diffusion-weighted MRI with apparent diffusion coefficient (ADC) maps and perfusion-weighted MRI by using a first-pass gadopentetate dimeglumine T2*-weighted gradient echo single-shot echo-planar sequence were performed. Relative cerebral blood volume (rCBV) ratios were obtained via the values of the capsular portions of the lesions and the normal white matter. All the abscesses had markedly hyperintense signals in trace diffusion images, whereas they had significant hypointense signals in ADC images. In perfusion-weighted images, the capsular portions of the abscesses demonstrated low colored areas compared with the normal white matter and the rCBV ratio calculated was 0.76 +/- 0.12 (mean +/- SD). All but two of the cystic tumors showed low signal intensity on trace diffusion-weighted images and high signal intensity on ADC maps. Hyperintense signal was found in two brain tumors mimicking brain abscesses on trace diffusion images. The rCBV values in high-grade gliomas and metastases were 5.51 +/- 2.08 and 4.58 +/- 2.19, respectively. The difference between abscesses and cystic tumors was statistically significant (P = 0.003). Perfusion MRI may allow the differentiation of pyogenic brain abscess from cystic brain tumors, making it a strong additional imaging modality in the early diagnosis of these two entities.     

Diffusion abnormality of deep gray matter in external capsular hemorrhage

BACKGROUND AND PURPOSE: To our knowledge, diffusion abnormality of the unaffected deep gray matter during striatocapsular hemorrhage has not been previously described in the literature. We report the presence of the diffusion abnormality separated from hematoma in patients with external capsular (lateral striatocapsular) hemorrhage and suggest the plausible mechanisms of diffusion signal intensity change. METHODS: We retrospectively reviewed MR images in 28 consecutive patients with spontaneous striatocapsular hemorrhage and evaluated signal intensity changes at sites separated from the hemorrhage and the lesions on diffusion-weighted (DW) images. Apparent diffusion coefficients (ADCs) of the lesions were measured, and volume changes in the deep gray matter were assessed at follow-up. RESULTS: On DW images, hyperintensity of deep gray matter was found in nine patients (25%). In all patients with DW imaging abnormality, the hemorrhage was located in the external capsule, and the interval from hemorrhagic ictus to MR imaging study was 8-54 days. Hyperintensity of the deep gray matter was seen in the caudate (n = 8), putamen (n = 7), thalamus (n = 5), and substantia nigra (n = 2). Mean relative ADC ratios of the diffusion abnormality were 0.76 +/- 0.10 in the caudate, 0.79 +/- 0.07 in the putamen, and 0.85 +/- 0.11 in the thalamus. DW imaging abnormality disappeared with mild atrophy in two patients who underwent follow-up imaging. CONCLUSION: External capsular hemorrhage may be uncommonly accompanied by diffusion abnormality in the striatum or thalamus at follow-up, and the lesion should not be misdiagnosed as new-onset infarction. Secondary neuronal degeneration may play an important role in the development of diffusion abnormality.     

创伤性颅脑损伤CT灌注成像的临床应用

目的探讨CT灌注成像(CTP)在创伤性颅脑损伤中应用的可能性,评估其对预后的判断价值。方法回顾性分析17例创伤性颅脑损伤病人CT灌注参数及图像,并与头颅CT平扫进行比较。结果 17例中CT平扫见创伤组织及周围脑实质低密度灶13例;CT灌注参数显示脑组织低灌注11例(64.7%),术区及挫伤脑组织高灌注4例(23.5%),2例未见明显脑组织灌注异常。低灌注者预后不良。结论对创伤性颅脑损伤行CT灌注有助于了解颅脑损伤后局部脑组织血流灌注情况,对预后判断提供帮助;在创伤性颅脑损伤的治疗中不仅注意脑低灌注,还应注意高灌注的存在。     

Diffusion-weighted imaging in the follow-up of treated high-grade gliomas: tumor recurrence versus radiation injury

BACKGROUND AND PURPOSE: Diffusion-weighted (DW) MR imaging is a means to characterize and differentiate morphologic features, including edema, necrosis, and tumor tissue, by measuring differences in apparent diffusion coefficient (ADC). We hypothesized that DW imaging has the potential to differentiate recurrent or progressive tumor growth from treatment-induced damage to brain parenchyma in high-grade gliomas after radiation therapy. METHODS: We retrospectively reviewed follow-up conventional and DW MR images obtained starting 1 month after completion of radiation treatment with or without chemotherapy for histologically proved high-grade gliomas. Eighteen patients with areas of abnormal enhancing tissue were identified. ADC maps were calculated from echo-planar DW images, and mean ADC values and ADC ratios (ADC of enhancing lesion to ADC of contralateral white matter) were compared with final diagnosis. Recurrence was established by histologic examination or by clinical course and a combination of imaging studies. RESULTS: Recurrence and nonrecurrence could be differentiated by using mean ADC values and ADC ratios. ADC ratios in the recurrence group showed significantly lower values (mean +/- SD, 1.43 +/- 0.11) than those of the nonrecurrence group (1.82 +/- 0.07, P <.001). Mean ADCs of the recurrent tumors (mean +/- SD, 1.18 +/- 0.13 x 10(-3) mm/s(2)) were significantly lower than those of the nonrecurrence group (1.40 +/- 0.17 x 10(-3) mm/s(2), P <.006). CONCLUSION: Assessment of ADC ratios of enhancing regions in the follow-up of treated high-grade gliomas is useful in differentiating radiation effects from tumor recurrence or progression.     

The study of cerebral hemodynamics in the hyperacute stage of fat embolism induced by triolein emulsion

PURPOSE: The purpose of this study was to evaluate the cerebral hemodynamic change in the hyperacute stage of cerebral fat embolism induced by triolein emulsion, by using MR perfusion imaging in cat brains. METHODS: By using the femoral arterial approach, the internal carotid arteries of 14 cats were infused with an emulsion of triolein 0.05 mL. T2-weighted (T2WI), diffusion-weighted (DWI), apparent diffusion coefficient (ADC) map, perfusion-weighted (PWI), and gadolinium-enhanced T1-weighted (Gd-T1WI) images were obtained serially at 30 minutes and 2, 4, and 6 hours after infusion. The MR images were evaluated qualitatively and quantitatively. Qualitative evaluation was performed by assessing the signal intensity of the serial MR images. Quantitative assessment was performed by comparing the signal-intensity ratio (SIR) of the lesions to the contralateral normal side calculated on T2WIs, Gd-T1WIs, DWIs, and ADC maps at each acquisition time and by comparing the relative cerebral blood volume (rCBV), cerebral blood flow (CBF), and mean transit times (MTT) of the lesions to the contralateral normal side calculated on PWI. RESULTS: In the qualitative evaluation of the MR images, the lesions showed hyperintensity on T2WIs, enhancement on the Gd-T1WIs, and isointensity on DWIs and the ADC maps. In the quantitative studies, SIRs on the Gd-T1WIs, DWIs, and ADC maps peaked at 2 hours after infusion. The SIRs on the T2WIs peaked at 4 hours after infusion and decreased thereafter. On PWIs, the rCBV, rCBF, and MTT of the lesion showed no significant difference from the contralateral normal side (P = .09, .30, and .13, respectively) and showed no significant change of time course (P = .17, .31, and .66, respectively). CONCLUSION: The embolized lesions induced by triolein emulsion showed no significant difference in cerebral hemodynamic parameters from those on the contralateral normal side. The result may suggest that consideration of the hemodynamic factor of embolized lesions is not necessary in further studies of the blood-brain barrier with triolein emulsion.     

Diffusion-weighted images in children with meningoencephalitis

PURPOSE: The objective of the study was to evaluate the maps of apparent diffusion coefficients (ADCs) and diffusion-weighted (DW) images in demonstrating meningoencephalitic lesions in children. MATERIALS AND METHODS: Between May 1998 and May 2000, 18 infants and children (4.5-190 months old) suffering from meningoencephalitis were included in the study. The diagnoses were bacterial meningoencephalitis in 8 and aseptic or viral in 10 patients. All 18 patients had brain MRI examinations. In the axial plane, three pulse sequences were performed on all patients: (1) FSE T2W images; (2) fast FLAIR images; (3) single-shot echoplanar DW images were acquired. Another 18 patients from the control group also received DW image examination. ADCs were computed for all regions on each DW image. RESULTS: The absolute values of CNRs of lesions on T2W (7.27+/-5.51), FLAIR (5.56+/-5.03) and DW (13.36+/-16.64) images were significantly greater than those on ADC maps (0.42+/-0.30) in the study group of patients (P<.01). In addition, absolute CNRs on DW images were significantly greater than on T2W and FLAIR images (P<.01). However, lesions on ADC maps in the study group have significantly greater CNRs than in the control group (0.13+/-0.12) (P<.01). CNRs on initial DW images from patients with atrophy or swelling of meningoencephalitic lesions were significantly different from the CNRs of those patients without significant changes in meningoencephalitic lesions (P=.02<.05). CONCLUSION: The DW image is a sensitive tool for detecting meningoencephalitic lesions and is better than FSE T2W and fast FLAIR images in CNRs. Diffusion MR techniques provides new ways to possibly predict the outcome of intracranial infectious diseases in children.     

Measurement of cerebral hemodynamics with perfusion-weighted MR imaging: comparison with pre- and post-acetazolamide 133Xe-SPECT in occlusive carotid disease

BACKGROUND AND PURPOSE: We generated regional cerebral blood volume (rCBV) and regional cerebral blood flow (rCBF) studies from dynamic susceptibility contrast-enhanced MR images after an intravenous bolus injection of contrast agent (perfusion-weighted imaging [PWI]) by applying indicator dilution theory. We used a multishot echo-planar imaging (EPI) sequence to obtain adequate arterial input function (AIF). Our purpose was to compare the cerebral hemodynamics measured by PWI with the rCBF values and cerebral perfusion reserve obtained by xenon-133 single-photon emission CT (133Xe-SPECT). METHODS: Eight patients with chronic internal carotid artery occlusion or stenosis were examined. PWI data were acquired using a multishot EPI sequence, and the AIF was determined automatically. Our procedure was based on indicator dilution theory and deconvolution analysis. To eliminate the effect of superficial vessels, the automatic threshold selection method was used. RESULTS: AIF was adequate to generate rCBF and rCBV images. The rCBF and rCBV images by PWI were superior to 133Xe-SPECT scans in spatial resolution, and the rCBF values obtained by PWI correlated well with those obtained by 133Xe-SPECT. The regions with severely decreased perfusion reserve, which were determined by pre- and post-acetazolamide 133Xe-SPECT, showed significantly lower rCBF and higher rCBV by PWI than did regions with normal and moderately decreased perfusion reserve. CONCLUSION: The rCBF and rCBV images generated by our procedure using PWI data appear to provide important clinical information for evaluating the degree of cerebral perfusion reserve impairment in patients with chronic ischemia.     

Magnetic resonance findings of primary central nervous system T-cell lymphoma in immunocompetent patients

PURPOSE: To describe the MR findings of primary central nervous system T-cell lymphoma (T-PCNSL) in immunocompetent patients. MATERIAL AND METHODS: Seven patients with pathologically proven T-PCNSL were included in our study. The number, location, shape, enhancement pattern, and signal intensity of the tumors were determined. Diffusion-weighted images (DWI) and perfusion-weighted images (PWI) were obtained in four and two patients, respectively. Apparent diffusion coefficients (ADCs) were generated, and regions of interest were defined in each lesion. RESULTS: Four patients with T-PCNSL had a single mass, while the others had multiple lesions (four, three, and two lesions, respectively). All seven cases of T-PCNSL had a supratentorial location: 12 in the subcortical area and 1 in the thalamus. No leptomeningeal involvement was noted. All tumors showed iso- to low T1 and iso- to slightly high T2 signal intensity to the adjacent gray matter. Rim enhancement was seen in 5 of the 7 patients (71.4%), while heterogeneous and homogeneous enhancement was seen in each of two. On DWI and ADC maps, the enhancing lesions showed slight hyperintensity in three patients (mean ADC ratio, 0.92 +/- 0.06) and iso-intensity in the other (ADC ratio, 1.02 +/- 0.05). Cystic areas consistent with necrosis were noted in three patients. High-signal intensity area in the cortex was noted on T1-weighted images in three patients, suggesting hemorrhage. In two patients, the same signal intensity area was noted within the mass. The two masses on the relative cerebral blood volume (rCBV) map demonstrated either similar or slightly higher signal intensity than that of the contralateral white matter. The rCBV ratios of these two masses were 1.27 +/- 0.16 and 1.35 +/- 0.2, respectively. CONCLUSION: T-PCNSLs show a predilection for a subcortical location, a relatively high incidence of cortical or intratumoral hemorrhage, rim enhancement, or cystic-areas consistent with necrosis on magnetic resonance imaging. The lower rCBV ratio of the tumor might be helpful in differentiating T-PCNSL from other brain tumors such as high-grade glioma.