一种基于指数型先验分布的正电子发射断层图像重建算法

背景:最大似然估计算法是正电子发射断层图像重建的经典算法,能够在信息量不足的情况下获得分辨率和噪声特性均优于滤波反投影重建的重建结果.但是MLEM算法具有不稳定性,即随迭代次数的增加,图像噪声反而会增加.目的:针对MLEM算法的图像噪声问题,提出一种基于指数型先验分布约束的MAP重建算法.方法:将指数先验分布代替传统MAP重建中的高斯先验,并用信噪比和归一化均方误差来判断重建质量.结果与结论:实验证明,该算法不仅能够抑制噪声,而且能够保持重建图像的边缘,不会造成过分平滑.     

小波先验在OSL重建算法中的应用

背景:MAP(最大后验)统计重建方法可以在重建过程中引入合适的先验知识达到去除噪声的目的.目的:根据小波系数的统计特性及能量平衡的原理对高频信息做相应的处理,并将多尺度的小波先验应用到OSL重建算法中以去除噪声.方法:实验从“变换域"的思想出发,在小波域上根据小波系数的统计特性及能量平衡原理对不同尺度的高频信息做相应的处理,并利用处理后的小波系数进行小波重建.结果与结论:基于小波先验的OSL算法比ML-EM算法重建的图像与测试模型的误差变小、相关性变大、噪声变少,重建图像变得比较平滑,视觉效果较清楚.     

小波先验在OSL重建算法中的应用

背景：MAP（最大后验）统计重建方法可以在重建过程中引入合适的先验知识达到去除噪声的目的。目的：根据小波系数的统计特性及能量平衡的原理对高频信息做相应的处理,并将多尺度的小波先验应用到OSL重建算法中以去除噪声。方法：实验从“变换域”的思想出发,在小波域上根据小波系数的统计特性及能量平衡原理对不同尺度的高频信息做相应的处理,并利用处理后的小波系数进行小波重建。结果与结论：基于小波先验的OSL算法比ML—EM算法重建的图像与测试模型的误差变小、相关性变大、噪声变少,重建图像变得比较平滑,视觉效果较清楚。     

医学CT图像伪影的对比分析研究

目的：探讨医学CT图像伪影的成因及减少伪影的方法。方法：对40例CT图像伪影的病例采用螺旋扫描方式,对自制模体在GE LightSpeed16层螺旋CT上设置不同参数进行扫描,分别改变螺距、层厚、重建间隔和模体位置,对阶梯状伪影进行分析。结果：CT图像伪影与被扫描物属性及成像的原理和技术有关;阶梯状伪影的大小与重建间隔和模体位置存在确定关系,伪影不仅随层厚的增加而增大,也随螺距的增加而增大。结论：CT图像伪影种类繁多,选择正确的扫描参数和方法对避免伪影的产生十分重要。     

基于交替投影的CT图像重建算法

目的 探讨基于交替投影的CT图像重建算法的可行性。方法 将CT图像的重建转化为凸集优化问题,将重建模型分解为多个约束,并确定其对应的凸集,通过交替投影的方式在其交集中找到可行解。对TV先验项构成的凸集的求解,通过定义TV函数的上方图集,利用点到这个凸集的切向超平面的连续投影,找到起始点到TV凸集最近的点。分别采用CPTV算法、TV-POCS算法和基于交替投影的CT图像重建算法对Shepp-Logan头部图像进行重建,比较不同算法对不同角度投影图像重建后的均方根误差（RMSE）。分别采用TV-POCS算法和基于交替投影的CT图像重建算法对小鼠脊椎轴位图像进行重建,比较两种算法的归一化均方距离（d）和归一化平均绝对距离（r）。结果 CPTV算法所重建的图像平滑性较差,伪影较多,而TV-POCS算法和基于交替投影的重建算法不仅有效抑制了噪声,还保护了图像的边缘,图像质量较高。基于交替投影的重建算法的RMSE比另外两种算法下降速度更快,收敛值更小。基于交替投影的重建算法重建图像的d和r值均小于TV-POCS算法（0.064 0 vs 0.262 4,0.073 7 vs 0.298 2）。结论 采用基于交替投影的重建算法重建有限角度的CT投影图像不需参数估计,且图像质量更高,收敛速度更快。     

一种快速校正CT环形伪影的方法

背景:环形伪影严重影响了CT图像质量,对图像后处理造成困难以及容易造成误诊断.目前去除环形伪影必不可少.目的:去除CT重建图像中的环形伪影,提高CT图像质量以及后续处理和量化分析的精度,便于诊断.方法:首先把含环形伪影的CT图像进行线性变换,将灰度图像转换成浮点类型的图像.接着由直角坐标变换到极坐标,这样原来的环形伪影就被变换成线形伪影.设计多维滤波器,计算每个象素滤波后均值以及方差,通过与阈值比较确定伪影范围.最后通过对伪影范围进行修正以及对图像进行坐标变换,变为灰度图像.结果与结论:通过Matlab 7.0软件设计程序,处理含环形伪影的CT图像.实验表明,此方法能有效快速地校正CT环形伪影,是一种属于图像后处理的校正方法.     

计算机断层扫描图像金属伪影校正方法研究现状

临床越来越多的患者接受金属植入手术。由金属植入物产生的金属伪影对利用CT图像进行术后评估与肿瘤诊断造成极大困难,易导致误漏诊。在滤波反投影重建算法、迭代重建算法基础上改进的校正方法近几十年来不断取得新的进展。本文对去除金属伪影技术的发展现状进行综述。     

3D均中值滤波参数的选取对3D OSEM重建图像的影响

目的 为了分析3D均值中值滤波参数的选取对OSEM重建图像的影响，采用3D均值中值滤波器对重建前的投影数据进行滤波处理，并调整参数进行定量分析。资料与方法 对分析模拟软件ASIM模拟的三维模体投影数据进行3D 均值中值滤波处理。利用开源断层图像重建软件STIR中的OSEM算法对滤波前后的投影数据进行重建，视觉和定量评估重建图像。结果 滤波参数与图像质量密切相关。值过大，重建图像边缘保持效果较差，图像过平滑。值过小，不能抑制噪声，导致重建图像细节模糊。 结论 重建图像的噪声大小以及边缘保持效果对滤波参数的选取是十分敏感的。可根据梯度分布直方图确定滤波参数选取范围，再结合梯度分布比从该范围内折中选择合适的参数，达到既去除噪声又保护图像边缘的目的。     

基于各向异性扩散和小波变换的磁共振图像降噪和增强方法

降噪是医学图像处理中一个非常重要的问题,传统去噪方法在降低噪声的同时会模糊图像的边缘,各向异性扩散滤波在降低图像噪声的同时能够使图像的边缘得到保持.利用小波变换可以对图像进行多尺度分解,使我们可以在不同尺度上对图像进行处理.本文利用各向异性扩散滤波对MRI图像进行降噪,然后利用平稳小波变换对图像进行增强处理.实验结果表明,该方法在有效去除噪声的同时能够增强图像的细节,有效地提高了图像的质量.     

多幅螺旋CT曲面重建技术在输尿管结石中的临床应用

目的：探讨多幅螺旋CT曲面重建技术对输尿管结石中的临床应用价值。方法：168例输尿管结石患者均采用MCN8000CT机扫描后选用冠状面进行曲面重建。结果：所有病例的曲面重建像均能清楚显示扩张的肾盂、输尿管及输尿管梗阻末端管腔内高密度结石影像。68例病例共获得174幅曲面重建像,其中图像清晰细腻、无运动伪影及阶梯状伪影165幅,占94．8％。图像质量一般,有轻度运动伪影及阶梯伪影9幅,占5．17％。结论：曲面重建技术可以使扩张肾盂、输尿管及输尿管梗阻末端管腔内的高密度结石影显示在一幅图像上,图像效果直观,对轴位扫描及多平面重建图像有重要的补充作用,同时对输尿管管腔内结石的临床治疗有较高的指导意义。     

Unsupervised lesion detection via image restoration with a normative prior

Unsupervised lesion detection is a challenging problem that requires accurately estimating normative distributions of healthy anatomy and detecting lesions as outliers without training examples. Recently, this problem has received increased attention from the research community following the advances in unsupervised learning with deep learning. Such advances allow the estimation of high-dimensional distributions, such as normative distributions, with higher accuracy than previous methods. The main approach of the recently proposed methods is to learn a latent-variable model parameterized with networks to approximate the normative distribution using example images showing healthy anatomy, perform prior-projection, i.e. reconstruct the image with lesions using the latent-variable model, and determine lesions based on the differences between the reconstructed and original images. While being promising, the prior-projection step often leads to a large number of false positives. In this work, we approach unsupervised lesion detection as an image restoration problem and propose a probabilistic model that uses a network-based prior as the normative distribution and detect lesions pixel-wise using MAP estimation. The probabilistic model punishes large deviations between restored and original images, reducing false positives in pixel-wise detections. Experiments with gliomas and stroke lesions in brain MRI using publicly available datasets show that the proposed approach outperforms the state-of-the-art unsupervised methods by a substantial margin, +0.13 (AUC), for both glioma and stroke detection. Extensive model analysis confirms the effectiveness of MAP-based image restoration.     

3D image segmentation of deformable objects with joint shape-intensity prior models using level sets

We propose a novel method for 3D image segmentation, where a Bayesian formulation, based on joint prior knowledge of the object shape and the image gray levels, along with information derived from the input image, is employed. Our method is motivated by the observation that the shape of an object and the gray level variation in an image have consistent relations that provide configurations and context that aid in segmentation. We define a maximum a posteriori (MAP) estimation model using the joint prior information of the object shape and the image gray levels to realize image segmentation. We introduce a representation for the joint density function of the object and the image gray level values, and define a joint probability distribution over the variations of the object shape and the gray levels contained in a set of training images. By estimating the MAP shape of the object, we formulate the shape-intensity model in terms of level set functions as opposed to landmark points of the object shape. In addition, we evaluate the performance of the level set representation of the object shape by comparing it with the point distribution model (PDM). We found the algorithm to be robust to noise and able to handle multidimensional data, while able to avoid the need for explicit point correspondences during the training phase. Results and validation from various experiments on 2D and 3D medical images are shown.     

320排CT心电编辑功能在冠脉支架置入术后的初步应用

目的 探讨320排螺旋CT心电编辑功能在冠心病冠脉支架成像的应用价值.方法 利用320排螺旋CT对14例有冠心病冠脉内支架置入术后的患者行冠脉血管成像,使用回顾性心电门控结合心电编辑软件对原始心电图进行编辑并重建,比较心电编辑前后重建的冠脉内支架显像质量.结果 14例患者冠脉内支架图像在心电编辑前图像模糊、出现伪影或分支血管缺失,其中编辑前诊断狭窄10例,1例无法显示冠脉支架及其远端分支而不能判断,仅3例诊断为支架通畅;心电编辑后冠脉内支架图像质量较前明显提高,诊断支架再狭窄4例,10例支架通畅;其中1例无法显示支架结构的病例支架近端狭窄.心电编辑前血管评分总均值为2.14±0.86,编辑后评分总均值为3.07±0.73,两者之间的差异有统计学意义（t =-13,P＜0.001）.结论 320排CT回顾性心电门控结合心电编辑技术能明显减轻或消除心律不齐及支架摆动、伪影而造成的图像失真,清楚显示支架形态及远端分支血管的变化,提高冠脉内支架的成像质量.     

听骨链螺旋CT 仿真内镜成像的最佳成像参数

目的 探讨听骨链螺旋ＣＴ仿真内镜（ＣＴＶＥ）成像的最佳成像参数。方法 选择２０例临床上除外耳部病变的病人进行薄层螺旋扫描。比较螺矩、重建算法和重建间隔对听骨链ＣＴＶＥ图像质量的影响。结果 随着Ｐｉｔｃｈ值增大图像质量降低,边缘算法的图像质量最佳,重建间隔越小图像质量越好。结论 听骨链ＣＴＶＥ成像的最佳成像参数是：层厚１．０ｍｍ,Ｐｉｔｃｈ１．０或１．５,显示视野９．６ｃｍ,边缘算法重建,重建间隔０     

3D均值中值滤波参数对3D有序子集期望最大化重建图像的影响

目的 采用3D均值中值滤波器对重建前投影数据进行滤波处理，并调整参数定量分析3D均值中值滤波参数选取对有序子集期望最大化（OSEM）重建图像的影响。方法 对分析模拟软件（ASIM）模拟的3D模体投影数据进行3D均值中值滤波处理。利用开源断层图像重建（STIR）软件中的OSEM算法对滤波前后投影数据进行重建，视觉和定量评估重建图像。结果 滤波参数K与图像质量密切相关。K值过大时重建图像边缘保持效果较差，图像过平滑；K值过小则不能抑制噪声，重建图像细节模糊。结论 重建图像噪声大小以及边缘保持效果对滤波参数K十分敏感。根据梯度分布直方图确定滤波参数选取范围，结合梯度分布比从中折中选择适当参数，既可去除噪声，又能保护图像边缘。     

A measurement system and image reconstruction in magnetic induction tomography

Magnetic induction tomography (MIT) is a technique for imaging the internal conductivity distribution of an object. In MIT current-carrying coils are used to induce eddy currents in the object and the induced voltages are sensed with other coils. From these measurements, the internal conductivity distribution of the object can be reconstructed. In this paper, we introduce a 16-channel MIT measurement system that is capable of parallel readout of 16 receiver channels. The parallel measurements are carried out using high-quality audio sampling devices. Furthermore, approaches for reconstructing MIT images developed for the 16-channel MIT system are introduced. We consider low conductivity applications, conductivity less than 5 S m(-1), and we use a frequency of 10 MHz. In the image reconstruction, we use time-harmonic Maxwell's equation for the electric field. This equation is solved with the finite element method using edge elements and the images are reconstructed using a generalized Tikhonov regularization approach. Both difference and static image reconstruction approaches are considered. Results from simulations and real measurements collected with the Philips 16-channel MIT system are shown.     

Left ventricular endocardial surface detection based on real-time 3D echocardiographic data.

OBJECTIVE: A new computerized semi-automatic method for left ventricular (LV) chamber segmentation is presented. METHODS: The LV is imaged by real-time three-dimensional echocardiography (RT3DE). The surface detection model, based on level set techniques, is applied to RT3DE data for image analysis. The modified level set partial differential equation we use is solved by applying numerical methods for conservation laws. The initial conditions are manually established on some slices of the entire volume. The solution obtained for each slice is a contour line corresponding with the boundary between LV cavity and LV endocardium. RESULTS: The mathematical model has been applied to sequences of frames of human hearts (volume range: 34-109 ml) imaged by 2D and reconstructed off-line and RT3DE data. Volume estimation obtained by this new semi-automatic method shows an excellent correlation with those obtained by manual tracing (r = 0.992). Dynamic change of LV volume during the cardiac cycle is also obtained. CONCLUSION: The volume estimation method is accurate; edge based segmentation, image completion and volume reconstruction can be accomplished. The visualization technique also allows to navigate into the reconstructed volume and to display any section of the volume.     

不同加载条件下粘固层厚度对瓷贴面的应力分布影响

目的分析不同加载条件下粘固层厚度对瓷贴面的应力分布影响。方法将上中切牙用环氧树脂包埋,精密机床逐层切削,数码成像。用Pro/ENGINEER软件生成瓷贴面模型,用Pro/MECHANICA软件进行有限元分析。结果在正中牙合加载状态下,减小粘固层厚度,瓷贴面的应力明显减小,在对刃牙合和深覆牙合两种加载方式下,减小粘固层厚度,各部位的应力有所减小,但变化不明显。正中牙合加载状态下切端对接型瓷贴面的颈部内侧出现一高应力区,而切端包绕型瓷贴面未出现。结论在正中牙合加载状态下,减小粘固层厚度可以降低瓷贴面的应力。