首页 | 官方网站   微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
2.
Characterizing the performance of image segmentation approaches has been a persistent challenge. Performance analysis is important since segmentation algorithms often have limited accuracy and precision. Interactive drawing of the desired segmentation by human raters has often been the only acceptable approach, and yet suffers from intra-rater and inter-rater variability. Automated algorithms have been sought in order to remove the variability introduced by raters, but such algorithms must be assessed to ensure they are suitable for the task. The performance of raters (human or algorithmic) generating segmentations of medical images has been difficult to quantify because of the difficulty of obtaining or estimating a known true segmentation for clinical data. Although physical and digital phantoms can be constructed for which ground truth is known or readily estimated, such phantoms do not fully reflect clinical images due to the difficulty of constructing phantoms which reproduce the full range of imaging characteristics and normal and pathological anatomical variability observed in clinical data. Comparison to a collection of segmentations by raters is an attractive alternative since it can be carried out directly on the relevant clinical imaging data. However, the most appropriate measure or set of measures with which to compare such segmentations has not been clarified and several measures are used in practice. We present here an expectation-maximization algorithm for simultaneous truth and performance level estimation (STAPLE). The algorithm considers a collection of segmentations and computes a probabilistic estimate of the true segmentation and a measure of the performance level represented by each segmentation. The source of each segmentation in the collection may be an appropriately trained human rater or raters, or may be an automated segmentation algorithm. The probabilistic estimate of the true segmentation is formed by estimating an optimal combination of the segmentations, weighting each segmentation depending upon the estimated performance level, and incorporating a prior model for the spatial distribution of structures being segmented as well as spatial homogeneity constraints. STAPLE is straightforward to apply to clinical imaging data, it readily enables assessment of the performance of an automated image segmentation algorithm, and enables direct comparison of human rater and algorithm performance.  相似文献   

3.
Although algorithm level re-computing techniques can trade-off the fault detection capability vs. time overhead of a Concurrent Error Detection (CED) scheme, they result in 100% time overhead when the strongest CED capability is achieved. Using the idle cycles in the data path to do the re-computation can reduce this time overhead. However, dependences between operations prevent the re-computation from fully utilizing the idle cycles. Deliberately breaking some of these data dependences can further reduce the time overhead associated with algorithm level re-computing. According to the experimental results the proposed technique, it brings time overhead down to 0-60% while the associated hardware overhead is from 12% to 50% depending on the design size.  相似文献   

4.
Recent developments to the MICHELLE electron gun and collector design tool are reported in this paper. The MICHELLE code is a new finite-element (FE) two-dimensional and three-dimensional electrostatic particle-in-cell code that has been designed to address the recent beam optics modeling and simulation requirements for vacuum electron devices, ion sources, and charged-particle transport. Problem classes specifically targeted include depressed collectors, gridded-guns, multibeam guns, sheet-beam guns, and ion thrusters. The focus of the development program is to combine modern FE techniques with improved physics models. The code employs a conformal mesh, including both structured and unstructured mesh architectures for meshing flexibility, along with a new method for accurate, efficient particle tracking. New particle emission models for thermionic beam representation are included that support primary emission, with an advanced secondary emission model. This paper reports on three significant advances to MICHELLE over the past year; hybrid structured/unstructured mesh support, a time-domain electrostatic algorithm, and an ion plasma model with charge exchange.  相似文献   

5.
许盈 《今日电子》2005,(5):96-98
从MPEG的发展史入手,着重介绍MPEG的音频压缩编码以有MP3编码器和解码器,并对MP3的发展现状和前景进行了较为准确的概括。  相似文献   

6.
时隙分配技术是VHF/UHF数据链中的一项关键技术,通过它可以提高系统的通信效率。在目前VHF/UHF数据链的基础上,提出了一种新的时隙分配高层算法:渐变分配策略,它主要是以固定分配方式为主,以竞争分配和动态分配为辅的一种新型时隙分配策略,兼有固定分配、竞争分配和动态分配的优点,同时又尽可能克服它们的缺点,以最小代价换来最大成效。  相似文献   

7.
传统的高校学生评教数据通常被教学管理部门作为教师绩效考核和评职的参考数据,对于教学管理部门并没有对评教结果数据进行深入研究探讨.基于此文中使用真实的评教样本,利用决策树分类算法对学生评教数据及教师的基本信息进行综合分析,从而生成决策树并从决策树中挖掘出影响教学质量的主要因素以及各因素对教学质量影响的强弱程度,以期为教师今后教学和教学管理部门制定教学改革措施提供参考依据.  相似文献   

8.
A three dimensional (3-D) reconstruction algorithm utilizing both linear interpolation and linear extrapolation was developed for the study of human prostatic cancer. The algorithm was validated by comparing the volumes and shapes of original to reconstructed objects. Synthetic objects of known geometry and wax models with shapes characteristic of prostatic carcinomas were assessed with standard planimetry and by the digital interpolation-extrapolation method. Volume and multifocality measurements obtained by reconstructing excised prostate glands using histologic maps obtained from whole-mount sections were tested. The new algorithm provided greater accuracy in determining tumor volumes than conventional methods. This model provides a basis for mathematical analysis of prostate cancer lesions.  相似文献   

9.
Passive macromodeling of high-speed package and interconnect modules characterized by measured/simulated data has generated immense interest during the recent years. This paper presents an efficient algorithm for transient simulation of interconnect networks characterized by measured/simulated data in the presence of other linear and nonlinear devices. A new set of linear constraints are proposed, which help in preserving the passivity of resulting macromodels. Examples are presented to demonstrate the validity and efficiency of the proposed algorithm.  相似文献   

10.
BD-2/GPS组合系统的设计与定位算法   总被引:1,自引:0,他引:1  
目前世界上4大主力卫星导航定位系统的兼容技术日益提高和完善,在这种客观需求下使多系统联合定位成为可能。为达到两种系统组合定位的目的,将中国北斗二号(BD-2)与GPS技术相融合,在BD-2单系统定位原理的基础上提出了BD-2/GPS构成的组合接收系统的设计思路和BD-2/GPS组合导航定位系统的数学解算方法。在定位算法上采用了加权最小二乘法对组合导航定位系统进行解算,并通过MATLAB软件对数据结果进行计算和分析,证明了此种算法的可行性和可靠性。  相似文献   

11.
提出将ID3决策树算法应用于体育成绩数据挖掘,以便对学生体能进行有效分析,从而提高体育教学管理的水平和质量。对现有成绩分析的不足进行分析,介绍了系统总体架构和数据挖掘实施流程,对ID3决策树算法的原理和其软件实现流程进行设计。采用Microsoft SQL Server 2012工具多维模式中的Analysis Services开发环境,实现决策树算法软件模块。系统运行结果显示,提出的系统能够为基于数据挖掘的学生成绩管理与分析提供有价值的科学依据。  相似文献   

12.
In this paper,we present coincidence-list-ordered sets expectation-maximization (COSEM), an algorithm for iterative image reconstruction directly from list-mode coincidence acquisition data. The COSEM algorithm is based on the ordered sets EM algorithm for binned data but has several extensions that makes it suitable for rotating two planar detector tomographs. We develop the COSEM algorithm and extend it to include analytic calculation of detection probability, noise reducing iterative filtering schemes, and on-the-fly attenuation correction methods. We present an adaptation of COSEM to the Varicam\VG camera and show results from clinical and phantom studies.  相似文献   

13.
本文提出的基于GPU的三维纹理映射算法通过编写顶点程序和片段程序,将传统的基于纹理面片的体绘制算法在GPU中实现.首先将体数据映射为三维纹理并将其载入到显存,接着通过对顶点着色程序和像素着色程序的编写将光线进入点、离开点的计算以及图像的合成运算移入GPU中,最后根据不同的采样点颜色混合公式实现不同的绘制效果.与传统的三...  相似文献   

14.
This paper presents a nonrigid registration two-dimensional/three-dimensional (2-D/3-D) framework and its phantom validation for subject-specific bronchoscope simulation. The method exploits the recent development of five degrees-of-freedom miniaturized catheter tip electromagnetic trackers such that the position and orientation of the bronchoscope can be accurately determined. This allows the effective recovery of unknown camera rotation and airway deformation, which is modelled by an active shape model (ASM). ASM captures the intrinsic variability of the tracheo-bronchial tree during breathing and it is specific to the class of motion it represents. The method reduces the number of parameters that control the deformation, and thus greatly simplifies the optimisation procedure. Subsequently, pq-based registration is performed to recover both the camera pose and parameters of the ASM. Detailed assessment of the algorithm is performed on a deformable airway phantom, with the ground truth data being provided by an additional six degrees-of-freedom electromagnetic (EM) tracker to monitor the level of simulated respiratory motion.  相似文献   

15.
基于雷达、红外的数据融合算法研究   总被引:1,自引:0,他引:1  
现代战争中,战场环境复杂,干扰严重,单一模式的武器不能满足要求,多模制导武器可以发挥各自模式的优点,其核心是多传感器的数据融合。文中对主动、红外传感器的数据融合方法进行研究,提出了数据融合的算法。采用加权最小二乘法将观测数据进行融合,将融合结果与前几个时刻融合数据进行拟合得到这一时刻的结果,此方法可充分利用各传感器信息,达到较好的数据融合效果。  相似文献   

16.
In this paper, a 2-D locally regularized strain estimation method for imaging deformation of soft biological tissues from radio-frequency (RF) ultrasound (US) data is introduced. Contrary to most 2-D techniques that model the compression-induced local displacement as a 2-D shift, our algorithm also considers a local scaling factor in the axial direction. This direction-dependent model of tissue motion and deformation is induced by the highly anisotropic resolution of RF US images. Optimal parameters are computed through the constrained maximization of a similarity criterion defined as the normalized correlation coefficient. Its value at the solution is then used as an indicator of estimation reliability, the probability of correct estimation increasing with the correlation value. In case of correlation loss, the estimation integrates an additional constraint, imposing local continuity within displacement and strain fields. Using local scaling factors and regularization increase the method's robustness with regard to decorrelation noise, resulting in a wider range of precise measurements. Results on simulated US data from a mechanically homogeneous medium subjected to successive uniaxial loadings demonstrate that our method is theoretically able to accurately estimate strains up to 17%. Experimental strain images of phantom and cut specimens of bovine liver clearly show the harder inclusions.  相似文献   

17.
陈光  张锡琨 《信息技术》2010,(5):148-152
随着信息技术的飞速发展,网络及网络信息安全技术已经影响到社会的政治、经济、文化和军事等各个领域,计算机网络的普及,数据安全传输问题受到人们的普遍关注.一个安全的网络信息系统应当确保所传输信息的完整性、保密性、不可否认性等.目前保障通信和网络安全技术的种类很多,其中数据加密技术是保障信息安全的核心的技术措施,信息加密也是现代密码学的主要组成部分.  相似文献   

18.
The class of geometric deformable models, also known as level sets, has brought tremendous impact to medical imagery due to its capability of topology preservation and fast shape recovery. In an effort to facilitate a clear and full understanding of these powerful state-of-the-art applied mathematical tools, the paper is an attempt to explore these geometric methods, their implementations and integration of regularizers to improve the robustness of these topologically independent propagating curves/surfaces. The paper first presents the origination of level sets, followed by the taxonomy of level sets. We then derive the fundamental equation of curve/surface evolution and zero-level curves/surfaces. The paper then focuses on the first core class of level sets, known as "level sets without regularizers." This class presents five prototypes: gradient, edge, area-minimization, curvature-dependent and application driven. The next section is devoted to second core class of level sets, known as "level sets with regularizers." In this class, we present four kinds: clustering-based, Bayesian bidirectional classifier-based, shape-based and coupled constrained-based. An entire section is dedicated to optimization and quantification techniques for shape recovery when used in the level set framework. Finally, the paper concludes with 22 general merits and four demerits on level sets and the future of level sets in medical image segmentation. We present applications of level sets to complex shapes like the human cortex acquired via MRI for neurological image analysis  相似文献   

19.
文章主要以数据挖掘算法的性能优化作为出发点,研究了相关的聚类算法,根据近些年来国际上对于聚类算法的原理、关键技术的研究分析了相关聚类个数K的相关作用和影响。希望通过文章的研究和报道能够对研究数据挖掘提供帮助,使得研究更够朝着更加有效和便捷的方向前进。  相似文献   

20.
用X射线衍射,扫描电子显微镜和透射电镜/能谱仪分析了Al2O3/TiB2和Al2O3/TiB2/SiCW陶瓷材料在1300℃氧化30小时后氧化层的相组成及显著结构。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司    京ICP备09084417号

京公网安备 11010802026262号