Real-time direct volume rendering in functional magnetic resonance imaging

Direct volume rendering is a visualization method that allows display of all information hidden in three-dimensional data sets of, for example, computed tomography or magnetic resonance imaging (MRI). In contrast to commonly used surface rendering methods, these algorithms need no preprocessing but suffer from a high computational complexity. A real-time rendering system, VIRIM (Vitec: Visualization Technology GmbH, Mannheim, Germany), cuts down rendering times of minutes on normal workstations to an interactive rate of 1 second or less. The immediate visual feedback allows interactive steering of the visualization process to achieve insight into the internal three-dimensional structure of objects. Additional information is obtained by using an interactive gray-value segmentation tool that both allows segmentation of the data set according to bone, tissue, and liquor and display of multifunctional data sets (e.g., functional MRI [fMRI] data sets). Thus, real-time direct volume rendering allows segmentation and volume data processing of functional and anatomical MR data sets simultaneously. As this method can be integrated in the clinical routine, it is of great importance for real-time motion artifact detection and the interpretation of fMRI data acquired during cognitive experiments with normal subjects and psychiatric patients. Because of the free programmability of VIRIM, more complex matching procedures are currently being investigated for future implementation.     

Volumetric analysis of mice lungs in a clinical magnetic resonance imaging scanner

Small animal models are widely used to study various pathologies. Magnetic resonance imaging (MRI) allows investigation of these animals in a non-invasive way. Therefore, the aim of our study was to develop and evaluate a low-cost approach to measure lung volumes in small animal MRI using a clinical scanner and a specially designed RF coil. Five mice (three of an established emphysema model and two controls) were investigated in a 1.0-T clinical scanner using a specially built small animal saddle coil and three different three-dimensional sequences; overall imaging time was approximately 16 min. Lung volumes were calculated from these images using an interactive watershed transform algorithm for semi-automatic image segmentation. The gold standard for the volume measurement was water displacement after surgical explantation. MRI measured volumes correlated significantly with ex vivo measurements on the explanted lungs (r = 0.99 to 0.89; p < 0.05). Mean lung volume in emphysema model mice was larger than in controls. High-resolution, small animal MRI using a clinical scanner is feasible for volumetric analysis and provides an alternative to a dedicated small animal scanner.     

Accuracy of computed tomography and magnetic resonance imaging in staging bronchogenic carcinoma

Sixty-three patients with non-small cell bronchogenic carcinoma were prospectively and independently assessed by computed tomography (CT) and magnetic resonance imaging (MRI) before surgery. Images were interpreted by four radiologists who had no knowledge of other imaging studies, except chest x-ray, and were blinded to surgical findings. The data were compared with pathologic and histologic findings. The accuracies of CT and MRI in determining tumor classification and assessing mediastinal and hilar lymph node metastases were compared. Sensitivity of CT in determining T factor was 78%, and specificity was 96%. The values for MRI were 84% and 96%, respectively. There was no significant difference between CT and MRI in staging tumors. MRI is more accurate than CT in diagnosing mediastinal invasion in staging superior sulcus tumors and complex tumors. There was no significant difference between the accuracies of CT and MRI in detecting mediastinal node metastases; the sensitivities were 82% and 90%, respectively, and specificities were 88% and 93%, respectively.     

基于关联分析及堆栈自编码器的气象敏感负荷功率估算方法

气象敏感负荷的逐年增长是夏季电网负荷不断攀升的重要原因,准确估算此类负荷功率对电网运行调度、估计地区需求侧响应能力均有益处。提出了改进典型相关分析方法,建立了负荷-气象非线性关联模型,基于此可计算历史负荷数据中的气象敏感负荷功率。建立了基于堆栈自编码器(SAE)的气象敏感负荷功率估算模型,利用SAE的无监督学习提取日负荷曲线的降维特征,利用关联模型的计算结果作为有标签样本训练估算模型的全连接层,从而由日负荷曲线直接获得气象敏感负荷功率曲线。基于实际电网数据的算例结果验证了所提方法的有效性。     

靶场光电经纬仪测量数据的误差分析及数据处理

光电经纬仪是在现代靶场测量中广泛应用的一种测量仪器,但是光电经纬仪在跟踪飞行目标的过程中,会因各种原因产生测角误差,影响弹道的测量精度。采用卡尔曼滤波的方法可以对光测数据进行有效的处理,提高其测量精度。本文通过对光电经纬仪测量数据的误差分析,建立了误差模型,并对测量数据进行了卡尔曼滤波,生成滤波数据弹道曲线。从而得到较为准确完整的弹道测试数据和外推数据,提高弹道数据获取的精度,最大限度地延伸弹道测量设备跟踪距离。     

Estimation of metabolite <Emphasis Type="Italic">T</Emphasis><Subscript>1</Subscript> relaxation times using tissue specific analysis,signal averaging and bootstrapping from magnetic resonance spectroscopic imaging data

Object A novel method of estimating metabolite T ₁ relaxation times using MR spectroscopic imaging (MRSI) is proposed. As opposed to conventional single-voxel metabolite T ₁ estimation methods, this method investigates regional and gray matter (GM)/white matter (WM) differences in metabolite T ₁ by taking advantage of the spatial distribution information provided by MRSI. Material and methods The method, validated by Monte Carlo studies, involves a voxel averaging to preserve the GM/WM distribution, a non-linear least squares fit of the metabolite T ₁ and an estimation of its standard error by bootstrapping. It was applied in vivo to estimate the T ₁ of N-acetyl compounds (NAA), choline, creatine and myo-inositol in eight normal volunteers, at 1.5 T, using a short echo time 2D-MRSI slice located above the ventricles. Results WM-T _1,NAA was significantly (P < 0.05) longer in anterior regions compared to posterior regions of the brain. The anterior region showed a trend of a longer WM T ₁ compared to GM for NAA, creatine and myo-Inositol. Lastly, accounting for the bootstrapped standard error estimate in a group mean T ₁ calculation yielded a more accurate T ₁ estimation. Conclusion The method successfully measured in vivo metabolite T ₁ using MRSI and can now be applied to diseased brain.     

Evolution of beta-amyloid induced neuropathology: magnetic resonance imaging and anatomical comparisons in the rodent hippocampus

Alzheimer’s disease (AD) is characterized by the anatomical appearance of β-amyloid (βA) plaques and neurofibrillary tangles. These changes are also associated with cyclical inflammation, oxidative damage and, as inferred from the autopsied brains of patients, progressive injury to neurons. Here, we report the short-term effects of an intrahippocampal injection of the toxic βA peptide fragment 25–35 in rats using quantitative magnetic resonance imaging (MRI) methods. Physiological changes within the cornu ammonis 1 (CA1) region of the hippocampus were monitored using a 1.5 T scanner at time points of 0.25, 1 and 24 h, and 7 and 14 days post injection. Spin echo T2-weighted (T2W) and diffusion weighted (DW) images were sequentially acquired. Apparent diffusion coefficients (ADC) were calculated and compared with histological alterations. A significant elevation in mean ADC values (17%) was observed in the ipsilateral CA1 at 14 days. The ADC changes were associated with disrupted pyramidal cells and nuclear lysis observed in histological sections. The contralateral CA1 exhibited a significant decrease in mean ADC of 15% at 14 days post treatment. Histological changes in the contralateral hippocampus suggested decreased neuronal density. T2W maps revealed no significant differences between the active βA 25–35 fragment and its non-active analog, βA 35–25. In conclusion, these results, based on changes in hippocampal ADC, demonstrate that the βA 25–35 treatment induced pathology consistent with edema and cellular necrosis. This is the first report describing the evolution of AD-like pathology in an animal model using DW imaging.     

基于有限元模型的电机零部件与整机结构振动关联特性

针对电机由多个复杂零部件组合而成导致系统振动故障难以准确诊断的问题,推导了含定子绕组、铁芯、端盖、转轴等电机零部件系统结构动力学方程,采用有限元法构建了某型异步电机零部件与整机系统动力学模型,并运用锤击法验证了建模法的有效性。通过分析无相对位移连接组件与整机有限元模型的固有频率值,得出底板、定子绕组、转轴、铁芯、前端盖及后端盖零部件对整机前三阶模态的贡献程度依次增大;研究零部件间连接方式对电机固有频率的影响,发现电机各阶固有频率随着零部件间连接刚度值增大而增加规律,这些可为电机振动故障分析与动力学设计提供参考。     

Transient global brain ischemia in the rat: spatial distribution, extension, and evolution of lesions evaluated by magnetic resonance imaging

A newly-developed model of transient global ischemia in the rat was evaluated by magnetic resonance imaging (MRI) in terms of localization of brain lesions, their extent and severity, and temporal evolution. Such a model, consisting of bilateral occlusion of common carotid arteries for 10 minutes and mild hypoxia (15% O₂) for 20 minutes induces delayed neuronal degeneration, necrosis, and gliosis (detected histologically and immunohistochemically). Ischemia was assessed by full suppression of spontaneous electroencephalographic activity. A “hybrid” T₂-/diffusion-weighted MR sequence enhancing more effectively the contrast between injured and intact tissues as compared to T₂-weighted MRI was used at 24, 48, 72, and 96 hours and at 7 days postischemia. Twenty hypoxic-ischemic rats showed a considerable variability in brain damage. In 8, there were no MRI-detectable lesions at any interval. In the other 12 rats, the severity and extension of neuronal damage varied markedly, but the lesions were always localized (monolaterally in 8 and bilaterally in 4 rats) in the occipital, temporal, or parietal cerebral cortex. Mainly, they were of intermediate severity or were severe (as assessed by MRI hyperintensity) and were accompanied by usually less severe lesions in the thalamus and/or caudate putamen. The hippocampus was affected moderately or severely in 4 of 12 rats. In most cases, there was at 48 hours a considerable growth in severity and/or extension of lesions, which usually remained stable at later intervals. In conclusion, MRI allowed us to follow brain lesions during the first week in this relatively simple and noninvasive model of transient global ischemia.     

Is there a correlation in breast carcinomas between tumor size and number of tumor vessels detected by gadolinium-enhanced magnetic resonance mammography?

Tumor vessels are known as a sign of malignancy in breast tumors. Is there a correlation between tumor size and the number of vessels in cases of breast tumor examined by dynamic gadolinium (Gd)-enhanced MR imaging? Eighteen patients (mean age, 46±7 years) underwent dynamic Gd-enhanced MR imaging of the breast by three-dimensional gradient echo sequence using thin-layer technique (2.5 mm) at 1.5T. The dynamic study included one precontrast and four postcontrast sequences (every 90 seconds) in coronal slices. Postprocessing by subtraction method and reconstruction in both transverse and sagittal planes were performed. All carcinomas showed rapid Gd enhancement. Tumor size (0.5 to 31.5 cm³; mean, 6.3±3.7 cm³) and number of vessels (1 to 10; mean, 3±2.1) were detected in summation of all three directions. A significant correlation was found between number of vessels and tumor size (r=0.787,p≤0.01). Breast tumor size significantly correlated with the number of vessels detected by Gd-enhanced MR mammography. The introduced method is a further important step in differentiating a carcinoma from a benign lesion.     

Transient global brain ischemia in young and aged rats: differences in severity and progression, but not localisation, of lesions evaluated by magnetic resonance imaging

A model of transient global brain ischemia consisting of bilateral occlusion of common carotid arteries for 10 min and mild hypoxia (15% O₂−85% N₂) for 20 min was studied by means of MRI in young and aged Fischer 344 rats (3–4 and 24–26 months, respectively). Ischemia was assessed by full suppression of spontaneous EEG activity, which reappeared and normalized similarly in the two age-groups. The survival of young with respect to aged rats was considerably higher both at 24 h (20/20, i.e. 100% vs 12/16, i.e. 75%) and at 48 h (16/20, i.e. 80% vs 6/16, i.e. 38%). The localisation of brain lesions, their severity and progression were evaluated by a diffusion-weighted MRI (DWI) sequence at 24 and 48 h post-ischemia. There were no DWI-detectable lesions in eight out of 20 young and two out of 12 aged rats. The localisation of DWI-detected lesions was rather similar in rats of the two age-groups. In fact, the cerebral cortex, mainly parietal, occipital and temporal lobes were damaged in 83% of young and 90% of aged rats. The respective percentages for the thalamus were 83 and 60%, for the striatum 58 and 50%, and for the hippocampus 25 and 30%. The lesions present in the cerebral cortex and the thalamus were considerably more severe in aged than in young rats. In conclusion, in spite of similar localisation of ischemic lesions in the two age-groups, their incidence was higher, appearance more rapid and severity more pronounced in aged with respect to young rats. This resulted in a considerably higher mortality of the former. The overall data indicate that the age issue is very important in experimental ischemia research.     

OPC UA及其事件模型在调度全域事件分析中的研究应用

研究在调度全域事件分析中全面应用OPC UA标准。分析当前系统中使用的GES信息模型、服务接口及调度事件分类,研究通过OPC UA告警和条件等规范定义的OPC UA事件模型描述调度全域事件,及通过OPC UA事件服务提供事件访问支持。对OPC UA事件服务与GES在事件定义和服务能力方面的差异给出了说明。以CIM模式、OPC UA事件分类为基础,建立事件分析应用的地址空间模型。建立基于OPC UA规范的事件分析应用,在统一地址空间中管理电网模型及事件等数据,完成事件综合分析。调度全域事件分析遵循OPC UA规范,提升了标准化程度、通信效率和安全性。     

直流机电暂态与电磁暂态模型在低频振荡分析中的比较

对交直流混合运行系统进行低频振荡分析时,直流系统通常采用机电暂态仿真模型。介绍了直流系统的机电暂态和电磁暂态两种仿真模型,在电力系统全数字仿真装置（ADPSS）平台上建立了EPRI36系统和某实际电网系统的机电暂态模型和机电-电磁暂态混合仿真模型,分别用于低频振荡分析。采用基于总体最小二乘-旋转不变技术的信号参数估计（TLS-ESPRIT）算法,分析故障后的振荡功率信号。提取低频振荡主导振荡频率、阻尼比等信息进行模态分析,并对分别利用两种仿真模型进行仿真得到的低频振荡分析的结果进行比较。结果表明,直流线路分别采取两种仿真模型时,仿真结果较为吻合,低频振荡分析的结果基本相同,机电暂态模型具有较高的实用价值。