针对现有的基于机载LiDAR数据的滤波算法未能充分利用数据提供的所有信息及其所采用的数据结构表达复杂、存在信息损失等缺陷,提出了一种灰度体素结构分割模型下的机载LiDAR 3D滤波算法。算法首先以综合利用机载LiDAR数据的高程及强度...针对现有的基于机载LiDAR数据的滤波算法未能充分利用数据提供的所有信息及其所采用的数据结构表达复杂、存在信息损失等缺陷,提出了一种灰度体素结构分割模型下的机载LiDAR 3D滤波算法。算法首先以综合利用机载LiDAR数据的高程及强度信息为目的将点云数据规则化为灰度(体素内激光点的平均强度的离散化表示)体素结构,然后基于各体素间的空间连通性和灰度相似性准则,将灰度体素结构分割并标记为若干个3D连通区域,最后依据地面与其它目标的高差特性提取与其对应的3D连通区域。算法优势在于:基于体素结构设计,为3D滤波算法;综合利用了地面目标的几何及辐射特征,对比传统滤波算法可应用于更复杂的场景;滤波结果为3D地面体素形式,可直接用于创建地面3D模型。实验采用国际摄影测量与遥感协会(International Society for Photogrammetry and Remote Sensing,ISPRS)提供的不同密度的机载LiDAR基准测试数据测试了邻域尺度参数的敏感性及提出的算法的有效性,并和其他经典滤波算法做对比。定量评价的结果表明,51邻域为最佳空间邻域尺度;点云密度为0.67点/m2的数据集1的滤波平均完整率、正确率及质量分别为0.9611、0.9248及0.8934;点云密度为4点/m2的数据集2的滤波平均完整率、正确率及质量分别为0.8490、0.8531及0.7404;对比其全经典滤波算法本文算法在高密度点云数据滤波时表现更佳。展开更多
In feature-based visual localization for small-scale scenes,local descriptors are used to estimate the camera pose of a query image.For large and ambiguous environments,learning-based hierarchical networks that employ...In feature-based visual localization for small-scale scenes,local descriptors are used to estimate the camera pose of a query image.For large and ambiguous environments,learning-based hierarchical networks that employ local as well as global descriptors to reduce the search space of database images into a smaller set of reference views have been introduced.However,since global descriptors are generated using visual features,reference images with some of these features may be erroneously selected.In order to address this limitation,this paper proposes two clustering methods based on how often features appear as well as their covisibility.For both approaches,the scene is represented by voxels whose size and number are computed according to the size of the scene and the number of available 3Dpoints.In the first approach,a voxel-based histogram representing highly reoccurring scene regions is generated from reference images.A meanshift is then employed to group the most highly reoccurring voxels into place clusters based on their spatial proximity.In the second approach,a graph representing the covisibility-based relationship of voxels is built.Local matching is performed within the reference image clusters,and a perspective-n-point is employed to estimate the camera pose.The experimental results showed that camera pose estimation using the proposed approaches was more accurate than that of previous methods.展开更多
人体体素模型包含体素数目巨大,在应用MCNP(Monte Carlo N-Particle Transport Code)进行剂量计算中通常采用重复结构形式,但是却存在几何正确性校验困难等问题。本文研究一种快速和准确的人体辐射计算模型可视化方法。该方法通过MCNP...人体体素模型包含体素数目巨大,在应用MCNP(Monte Carlo N-Particle Transport Code)进行剂量计算中通常采用重复结构形式,但是却存在几何正确性校验困难等问题。本文研究一种快速和准确的人体辐射计算模型可视化方法。该方法通过MCNP输入文件中的栅元描述获取相同材料的体素信息,对其赋予三维坐标值并深度合并。在保持几何形状不变的前提下,成功构建器官模型,实现了对其进行三维显示与交互。测试结果验证了该方法对于人体重复结构计算模型几何校验的正确性与高效性。展开更多
The use of computers in facilitating their processing and analysis has become necessary with the increaseing size and number of medical images. In particular, computer algorithms for the delineation of anatomical stru...The use of computers in facilitating their processing and analysis has become necessary with the increaseing size and number of medical images. In particular, computer algorithms for the delineation of anatomical structures and other regions of interest, which are called image segmentation, play a vital role in numerous biomedical imaging applications such as the quantification of tissue volumes, diagnosis, localization of pathology, study of anatomical structure, treatment planning, and computer-integrated surgery. In this paper, a 3D volume extraction algorithm was proposed for segmentation of cerebrovascular structure on brain MRA data sets. By using a priori knowledge of cerebrovascular structure, multiple seed voxels were automatically identified on the initially thresholded image. In the consideration of the preserved voxel connectivity—which is defined as 6-connectivity with joint faces, 18-connectivity with joint edges, and 26-connectivity with joint corners— the seed voxels were grown within the cerebrovascular structure area throughout 3D volume extraction process. This algorithm provided better segmentation results than other segmentation methods such as manual, and histogram thresholding approach. This 3D volume extraction algorithm is also applicable to segment the tree-like organ structures such as renal artery, coronary artery, and airway tree from the medical imaging modalities.展开更多
Many studies have shown the functional relevance of cross-modal plasticity in blind men. In order to study the changes of their brain structure, voxel-based morphometry （VBM） methods are used. The regional gray matt...Many studies have shown the functional relevance of cross-modal plasticity in blind men. In order to study the changes of their brain structure, voxel-based morphometry （VBM） methods are used. The regional gray matter （GM） and white matter （WM） concentrations of magnetic resonance （MR） images from 11 blind people and 9 sighted control subjects are compared using standard VBM. Optimized VBM is also discussed to measure the absolute local volume of GM or WM. Consistent results are achieved by statistical analysis with these methods. There are distinct differences not only in visual cortex but also the sensory area, auditory area and motor area. GM concentrations in blind men significantly decreased in Brodmann 7 and 22. While in Brodmann 18 and 19, GM concentration increased. GM volumes decreased in Brodmann 3, 4, 6, 9 and 45. On the other hand, both WM concentration and volume increased in Brodmann 7. These results suggest that early visual deprivation can lead to changes in the brain structural anatomy which is consistent with the cortical cross-modal reorganization found by functional imaging. It may help to discover the relationship between the brain structural anatomy and the brain functional data of blind men at a macroscopic level from neuroimaging perspective.展开更多
Our previous study used regional homogeneity analysis and found that activity in some brain areas of patients with ischemic stroke changed significantly. In the current study, we examined structural changes in these b...Our previous study used regional homogeneity analysis and found that activity in some brain areas of patients with ischemic stroke changed significantly. In the current study, we examined structural changes in these brain regions by taking structural magnetic resonance imaging scans of 11 ischemic stroke patients and 15 healthy participants, and analyzing the data using voxel-based morphometry. Compared with healthy participants, patients exhibited higher gray matter density in the left inferior occipital gyrus and right anterior white matter tract. In contrast, gray matter density in the right cerebellum, left precentral gyrus, right middle frontal gyrus, and left middle temporal gyrus was less in ischemic stroke patients. The changes of gray matter density in the middle frontal gyrus were negatively associated with the clin- ical rating scales of the Fugl-Meyer Motor Assessment （r = -0.609, P = 0.047） and the left middle temporal gyrus was negatively correlated with the clinical rating scales of the nervous functional deficiency scale （r = -0.737, P = 0.010）. Our findings call objectively identify the functional abnormality in some brain regions of ischemic stroke patients.展开更多
Idiopathic rapid eye movement sleep behavior disorder(iRBD) is often a precursor to neurodegenerative disease. However, voxel-based morphological studies evaluating structural abnormalities in the brains of iRBD patie...Idiopathic rapid eye movement sleep behavior disorder(iRBD) is often a precursor to neurodegenerative disease. However, voxel-based morphological studies evaluating structural abnormalities in the brains of iRBD patients are relatively rare. This study aimed to explore cerebral structural alterations using magnetic resonance imaging and to determine their association with clinical parameters in iRBD patients. Brain structural T1-weighted MRI scans were acquired from 19 polysomnogram-confirmed iRBD patients(male:female 16:3; mean age 66.6 ± 7.0 years) and 20 age-matched healthy controls(male:female 5:15; mean age 63.7 ± 5.9 years). Gray matter volume(GMV) data were analyzed based on Statistical Parametric Mapping 8, using a voxel-based morphometry method and two-sample t-test and multiple regression analysis. Compared with controls, iRBD patients had increased GMV in the middle temporal gyrus and cerebellar posterior lobe, but decreased GMV in the Rolandic operculum, postcentral gyrus, insular lobe, cingulate gyrus, precuneus, rectus gyrus, and superior frontal gyrus. iRBD duration was positively correlated with GMV in the precuneus, cuneus, superior parietal gyrus, postcentral gyrus, posterior cingulate gyrus, hippocampus, lingual gyrus, middle occipital gyrus, middle temporal gyrus, and cerebellum posterior lobe. Furthermore, phasic chin electromyographic activity was positively correlated with GMV in the hippocampus, precuneus, fusiform gyrus, precentral gyrus, superior frontal gyrus, cuneus, inferior parietal lobule, angular gyrus, superior parietal gyrus, paracentral lobule, and cerebellar posterior lobe. There were no significant negative correlations of brain GMV with disease duration or electromyographic activity in iRBD patients. These findings expand the spectrum of known gray matter modifications in iRBD patients and provide evidence of a correlation between brain dysfunction and clinical manifestations in such patients. The protocol was approved by the Ethics Committee of Huashan Hospital(approval No展开更多
文摘针对现有的基于机载LiDAR数据的滤波算法未能充分利用数据提供的所有信息及其所采用的数据结构表达复杂、存在信息损失等缺陷,提出了一种灰度体素结构分割模型下的机载LiDAR 3D滤波算法。算法首先以综合利用机载LiDAR数据的高程及强度信息为目的将点云数据规则化为灰度(体素内激光点的平均强度的离散化表示)体素结构,然后基于各体素间的空间连通性和灰度相似性准则,将灰度体素结构分割并标记为若干个3D连通区域,最后依据地面与其它目标的高差特性提取与其对应的3D连通区域。算法优势在于:基于体素结构设计,为3D滤波算法;综合利用了地面目标的几何及辐射特征,对比传统滤波算法可应用于更复杂的场景;滤波结果为3D地面体素形式,可直接用于创建地面3D模型。实验采用国际摄影测量与遥感协会(International Society for Photogrammetry and Remote Sensing,ISPRS)提供的不同密度的机载LiDAR基准测试数据测试了邻域尺度参数的敏感性及提出的算法的有效性,并和其他经典滤波算法做对比。定量评价的结果表明,51邻域为最佳空间邻域尺度;点云密度为0.67点/m2的数据集1的滤波平均完整率、正确率及质量分别为0.9611、0.9248及0.8934;点云密度为4点/m2的数据集2的滤波平均完整率、正确率及质量分别为0.8490、0.8531及0.7404;对比其全经典滤波算法本文算法在高密度点云数据滤波时表现更佳。
基金supported by the Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(NRF-2018R1D1A1B07049932).
文摘In feature-based visual localization for small-scale scenes,local descriptors are used to estimate the camera pose of a query image.For large and ambiguous environments,learning-based hierarchical networks that employ local as well as global descriptors to reduce the search space of database images into a smaller set of reference views have been introduced.However,since global descriptors are generated using visual features,reference images with some of these features may be erroneously selected.In order to address this limitation,this paper proposes two clustering methods based on how often features appear as well as their covisibility.For both approaches,the scene is represented by voxels whose size and number are computed according to the size of the scene and the number of available 3Dpoints.In the first approach,a voxel-based histogram representing highly reoccurring scene regions is generated from reference images.A meanshift is then employed to group the most highly reoccurring voxels into place clusters based on their spatial proximity.In the second approach,a graph representing the covisibility-based relationship of voxels is built.Local matching is performed within the reference image clusters,and a perspective-n-point is employed to estimate the camera pose.The experimental results showed that camera pose estimation using the proposed approaches was more accurate than that of previous methods.
文摘人体体素模型包含体素数目巨大,在应用MCNP(Monte Carlo N-Particle Transport Code)进行剂量计算中通常采用重复结构形式,但是却存在几何正确性校验困难等问题。本文研究一种快速和准确的人体辐射计算模型可视化方法。该方法通过MCNP输入文件中的栅元描述获取相同材料的体素信息,对其赋予三维坐标值并深度合并。在保持几何形状不变的前提下,成功构建器官模型,实现了对其进行三维显示与交互。测试结果验证了该方法对于人体重复结构计算模型几何校验的正确性与高效性。
文摘The use of computers in facilitating their processing and analysis has become necessary with the increaseing size and number of medical images. In particular, computer algorithms for the delineation of anatomical structures and other regions of interest, which are called image segmentation, play a vital role in numerous biomedical imaging applications such as the quantification of tissue volumes, diagnosis, localization of pathology, study of anatomical structure, treatment planning, and computer-integrated surgery. In this paper, a 3D volume extraction algorithm was proposed for segmentation of cerebrovascular structure on brain MRA data sets. By using a priori knowledge of cerebrovascular structure, multiple seed voxels were automatically identified on the initially thresholded image. In the consideration of the preserved voxel connectivity—which is defined as 6-connectivity with joint faces, 18-connectivity with joint edges, and 26-connectivity with joint corners— the seed voxels were grown within the cerebrovascular structure area throughout 3D volume extraction process. This algorithm provided better segmentation results than other segmentation methods such as manual, and histogram thresholding approach. This 3D volume extraction algorithm is also applicable to segment the tree-like organ structures such as renal artery, coronary artery, and airway tree from the medical imaging modalities.
基金the National Natural Science Foundation of China (30400136)
文摘Many studies have shown the functional relevance of cross-modal plasticity in blind men. In order to study the changes of their brain structure, voxel-based morphometry （VBM） methods are used. The regional gray matter （GM） and white matter （WM） concentrations of magnetic resonance （MR） images from 11 blind people and 9 sighted control subjects are compared using standard VBM. Optimized VBM is also discussed to measure the absolute local volume of GM or WM. Consistent results are achieved by statistical analysis with these methods. There are distinct differences not only in visual cortex but also the sensory area, auditory area and motor area. GM concentrations in blind men significantly decreased in Brodmann 7 and 22. While in Brodmann 18 and 19, GM concentration increased. GM volumes decreased in Brodmann 3, 4, 6, 9 and 45. On the other hand, both WM concentration and volume increased in Brodmann 7. These results suggest that early visual deprivation can lead to changes in the brain structural anatomy which is consistent with the cortical cross-modal reorganization found by functional imaging. It may help to discover the relationship between the brain structural anatomy and the brain functional data of blind men at a macroscopic level from neuroimaging perspective.
基金financially supported by the National Program on Key Basic Research Project of China(973 Program)No.2012CB518501the National Natural Science Foundation of China,No.81072864
文摘Our previous study used regional homogeneity analysis and found that activity in some brain areas of patients with ischemic stroke changed significantly. In the current study, we examined structural changes in these brain regions by taking structural magnetic resonance imaging scans of 11 ischemic stroke patients and 15 healthy participants, and analyzing the data using voxel-based morphometry. Compared with healthy participants, patients exhibited higher gray matter density in the left inferior occipital gyrus and right anterior white matter tract. In contrast, gray matter density in the right cerebellum, left precentral gyrus, right middle frontal gyrus, and left middle temporal gyrus was less in ischemic stroke patients. The changes of gray matter density in the middle frontal gyrus were negatively associated with the clin- ical rating scales of the Fugl-Meyer Motor Assessment （r = -0.609, P = 0.047） and the left middle temporal gyrus was negatively correlated with the clinical rating scales of the nervous functional deficiency scale （r = -0.737, P = 0.010）. Our findings call objectively identify the functional abnormality in some brain regions of ischemic stroke patients.
基金supported by the China-US Biomedical Collaborative Research Program,No.81361120393(to CTZ)the National Natural Science Foundation of China,No.81401135(to PW),81671239(to CTZ)the Shanghai Sailing Program,No.18YF1403100(to JJG)
文摘Idiopathic rapid eye movement sleep behavior disorder(iRBD) is often a precursor to neurodegenerative disease. However, voxel-based morphological studies evaluating structural abnormalities in the brains of iRBD patients are relatively rare. This study aimed to explore cerebral structural alterations using magnetic resonance imaging and to determine their association with clinical parameters in iRBD patients. Brain structural T1-weighted MRI scans were acquired from 19 polysomnogram-confirmed iRBD patients(male:female 16:3; mean age 66.6 ± 7.0 years) and 20 age-matched healthy controls(male:female 5:15; mean age 63.7 ± 5.9 years). Gray matter volume(GMV) data were analyzed based on Statistical Parametric Mapping 8, using a voxel-based morphometry method and two-sample t-test and multiple regression analysis. Compared with controls, iRBD patients had increased GMV in the middle temporal gyrus and cerebellar posterior lobe, but decreased GMV in the Rolandic operculum, postcentral gyrus, insular lobe, cingulate gyrus, precuneus, rectus gyrus, and superior frontal gyrus. iRBD duration was positively correlated with GMV in the precuneus, cuneus, superior parietal gyrus, postcentral gyrus, posterior cingulate gyrus, hippocampus, lingual gyrus, middle occipital gyrus, middle temporal gyrus, and cerebellum posterior lobe. Furthermore, phasic chin electromyographic activity was positively correlated with GMV in the hippocampus, precuneus, fusiform gyrus, precentral gyrus, superior frontal gyrus, cuneus, inferior parietal lobule, angular gyrus, superior parietal gyrus, paracentral lobule, and cerebellar posterior lobe. There were no significant negative correlations of brain GMV with disease duration or electromyographic activity in iRBD patients. These findings expand the spectrum of known gray matter modifications in iRBD patients and provide evidence of a correlation between brain dysfunction and clinical manifestations in such patients. The protocol was approved by the Ethics Committee of Huashan Hospital(approval No
文摘目的采用基于体素的形态学测量(voxel-based morphometry,VBM)方法探讨终末期肾病(end stage renal disease,ESRD)患者脑灰质体积变化及其与执行功能障碍的相关性。材料与方法41名ESRD患者(ESRD组)与年龄、性别、教育水平相匹配的41名健康志愿者(正常对照组)均接受头颅3D-T1WI MRI扫描及执行功能行为学测试,采用VBM方法测量两组脑灰质体积,使用SPM 12软件对两组脑灰质体积进行双样本独立t检验比较差异性,并将ESRD组差异脑区灰质体积与执行功能测试评分进行Pearson相关分析。结果与正常对照组相比,ESRD组前扣带回、双侧中扣带回、双侧岛叶、左侧额中回、左侧颞横回、左侧海马及左侧尾状核灰质体积显著变小(P<0.05,FWE校正)。前扣带回、左侧中扣带回及左侧岛叶灰质体积与连线测试A(trail making test A,TMT-A)评分存在显著负相关(P<0.05),前扣带回、双侧岛叶、左侧额中回、左侧颞横回及左侧海马灰质体积与数字符号转换测试(digit symbol substitution test,DSST)评分存在显著正相关(P<0.05)。结论ESRD患者脑灰质结构存在异常,且扣带回、前额叶及颞叶部分脑区灰质萎缩与患者执行功能损害程度相关。
