CT9800机器操作使用经验介绍

本文重点介绍了在进行CT断层X-线摄影时,如何灵活应用标准、软组织和骨结构等三种重建图像的软件,既能显著缩短图像重建的时间,又不会遗漏病变的影像。     

颅脑CT扫描技术方法的改进

本文阐述了在颅脑计算机断层射线摄影的扫描过程中,改变扫描层平面距离的情况,即把该距离由10mm增加为11mm,从而形成一个宽1mm的未扫描空间。作者认为,由于一般的CT设备空间解像力低,形成的像素尺寸为1.0×1.0mm,因此,这些未扫描区不会影响诊断。     

CT增强扫描在肺结节病诊断中的价值

目的:探讨肺结节病的多层螺旋CT影像学表现,特别是增强扫描后的特征,以提高本病的诊断水平。方法:回顾性分析经病理及临床证实的32例肺结节病患者的临床资料和CT表现。结果:32例结节病中,肺门、纵隔淋巴结肿大31例,特征为对称性肺门淋巴结肿大伴纵隔淋巴结肿大,不融合,增强后呈中等度较均匀强化;肺内病变25例,多表现为沿支气管血管束分布网状结节。结论:肺结节病的CT表现具有一定特征性,增强CT扫描有助于提高诊断正确率。     

CT、MR技术进展与核医学影像

医学功能影像领域各种新技术层出不穷,已成为多学科交叉的研究热点。特别是CT、MR功能成像技术发展迅速,在中枢神经系统疾病、心血管系统疾病、以及肿瘤诊断中已有较多基础和临床初步应用结果,且部分技术发展前景广阔,这对核医学影像所具有的传统优势在一定程度上带来了冲击或挑战。作为核医学工作者,应主动适应新世纪相关影像设备、技术发展带来的机遇和挑战,不断丰富和拓展核素显像在医学实践中所具有的特色和重要作用,使核素显像能够与其它影像诊断技术形成优势互补之势,才能立于不败之地。     

薄层螺旋CT诊断眼眶内侧壁骨折的应用价值

目的:探讨薄层螺旋CT诊断眶内侧壁骨折的应用价值.方法:对53例患者或志愿者行常规轴位及薄层轴位、冠位扫描.分别将常规轴位扫描图像与薄层轴位扫描图像及薄层冠位扫描图像与轴位薄层扫描MPR冠状位重建图像进行比较.结果:前组图像对病变显示率二者有明显差异(P＜0.001),后组无明显差异.结论:仅薄层CT扫描即可精确诊断眶内侧壁骨折,尤以轴位图像显示为佳.     

薄层螺旋CT诊断眼眶内侧壁骨折的应用价值

目的:探讨薄层螺旋CT诊断眶内侧壁骨折的应用价值。方法:对53例患者或志愿者行常规轴位及薄层轴位、冠位扫描。分别将常规轴位扫描图像与薄层轴位扫描图像及薄层冠位扫描图像与轴位薄层扫描MPR冠状位重建图像进行比较。结果:前组图像对病变显示率二者有明显差异(P<0．001),后组无明显差异。结论:仅薄层CT扫描即可精确诊断眶内侧壁骨折,尤以轴位图像显示为佳。     

浅谈医用CT机计量检定中性能模体的定位

在JJG961-2001《医用诊断计算机断层摄影装置(CT)X射线辐射源》国家计量检定规程中,关于性能模体的定位不很具体。但是性能模体的定位准确与否,将直接影响医用CT机的计量检定结果。性能模体的定位,实际上就是实现性能模体的任意一个横断面与CT机的扫描面平行,而且所得到的横断面图像的对称中心与扫描野的中心重合的过程。为了叙述方便,我们把沿扫描床移动的方向定为Z方向,把水平方向定为X方向,把竖直方向定为Y方向。我们使用的性能模体是VIC鄄TOREEN-AAPM检测模体。这里暂以该性能模体为例,谈一下模体的定位。为工作方便,我们建…     

CT机扫描条件对CT值和辐射剂量指数的影响

随着使用的日益广泛．X射线计算机断层摄影装置（Xray Computerized Tomography Scanner，简称CT）已经成为医用诊断中最重要的装置之一，其成像质量对患者病情的诊断有直接的影响；同时，由它带来的辐射剂量控制的问题也越来越受到各国的重视。德国放射防护联邦局1994年的调查结果显示，CT扫描仅仅为所有放射检查的4％，但却是医疗放射人群剂量的1／3；而放射剂量的增加将直接危及人体健康，如增加致癌几率等。我国于2001年制定了JJG961—200l《医用诊断计算机断层摄影装置（CT）X射线辐射源》检定规程，对CT成像质量及剂量指数作出了明确的要求和规定．为CT成像质量及辐射剂量的控制提供了明确的参考。CT成像质量及辐射剂量会受到各方面因素的影响，如管球、探测器、机器类型及使用年限、扫描方式和扫描条件等。在临床单层轴向扫描中，管电压、管电流、曝光时间、层厚、照射野等扫描条件对于CT成像质量及辐射剂量有直接的影响。在本文中，我们根据实际检定工作中得到的临床数据．在其他条件相同的情况下，分析了管电压、管电流和曝光时间对CT值和辐射剂量指数的影响，这将有利于在CT的临床使用中更好地选择扫描条件，保障患者的辐射安全．同时对根据CT值进行临床诊断提供参考依据。     

三维 CT 在锥角增大时对重建图像质量的影响

通过分析圆柱状物体在不同锥角时对重建图像质量的影响 ,从而得出传统三维 CT适宜于小锥角(大约 6°)情况时的重建的结论     

医用CT机检定操作中的问题与解决方案

<正>0引言医用诊断螺旋计算机断层摄影装置(Computed Tomography简称CT)是现代医学诊断不可或缺的影像设备,其影像质量与疾病的准确诊断密切相关;同时作为X射线辐射源,CT检查时辐射剂量的控制也不容忽视。为此,我国制定了医用CT机X射线辐射源检定规程并于2007年颁布实施,对于保障CT质量性能的可靠、诊断结果的准确和患者的辐射     

The construction and use of convex hulls in limited-angle computerized tomography

A method is developed to construct the convex hull of an object and make use of it in limited-angle x-ray computerized tomography (CT). The convex hull of an object is the smallest convex region containing the object, and therefore it can serve as boundary information in the reconstruction of the object from limited-angle data. Two methods, the intersection version and the superimposition version, of constructing the convex hull of an object from x-ray data are presented. It is shown that the intersection version is very efficient when the noise is very low, whereas the superimposition version is more stable with respect to noise. The usefulness and the construction of the convex hulls of embedded flaws in industrial x-ray CT are also studied. It is demonstrated with simulated data that the use of convex hulls makes it possible to reconstruct high-quality images from limited-angle data.     

Study on beam geometry and image reconstruction algorithm in fast neutron computerized tomography at NECTAR facility

Investigations on the fast neutron beam geometry for the NECTAR facility are presented. The results of MCNP simulations and experimental measurements of the beam distributions at NECTAR are compared. Boltzmann functions are used to describe the beam profile in the detection plane assuming the area source to be set up of large number of single neutron point sources. An iterative algebraic reconstruction algorithm is developed, realized and verified by both simulated and measured projection data. The feasibility for improved reconstruction in fast neutron computerized tomography at the NECTAR facility is demonstrated.     

Design and implementation of a portable computerized axial tomography system for field use

A prototype, portable computerized axial tomography (CAT) scanner for in-field use has been designed, built and tested by researchers at the University of Missouri — Columbia. The device weighs 24 kg (53 lbs), is battery-powdered (providing eight hours of use without recharge), and fits into two small suitcases. A typical scan provides a low resolution (1.0 cm) image of an object 30 cm (12 in.) in diameter with a density of 0.65 g/cm³ in eight minutes of imaging and data reconstruction time. The resulting image is displayed in the field on the system's portable computer system.     

氦氖激光CT胶片的研制

氦氖激光CT胶片充分利用激光的单色性、高强度等特点，可使医用X线计算机体层摄影获得清晰度更高和层次更丰富的射线照相影像，为医疗诊断提供极其重要的信息。本文扼要介绍了该胶片研制过程中所研究的主要技术课题和取得的成果；经对比检测，其实用性能可达到进口同类产品水平。     

Limited-angle computed tomography for sandwich structures using data fusion

Both conventional and limited-angle computed-tomography (CT) are ill-posed problems, but where conventional CT has a small null space with few dimensions, limited-angle CT has a much larger null space and is severely ill-posed. The nature of the ill-posedness of limited-angle CT dictates that any limited-angle reconstruction method must interpolate from partial data in the Fourier domain. Large aluminum-core sandwich structures, such as those of aircraft control surfaces, simultaneously prevent full range data acquisition for CT and have face sheets that lie primarily in the limited-angle Radon transform null space. Consequently, interpolation of missing data is not possible and limited-angle CT for large sandwich structures is not feasible. This paper presents a novel method for limited-angle CT that addresses this problem. The method uses constraint-based data fusion to reduce the null space of the problem in a manner consistent with the specimen. Measurements of spatial support and face sheet thickness provide data for the additional constraints. By using the method, accurate reconstruction of sandwich structures becomes possible, where it would otherwise be impossible. The method of convex projections solves the inverse problem posed by the fusion system well because it is fast (for this problem) and easily incorporates the fusion constraints. Experimental results based on synthetic data show the improvement in reconstruction accuracy obtained by the fusion method. Real data results show the successful application of the method to a plexiglass phantom.     

Radiography and partial tomography of wood with thermal neutrons

The effective high neutron scattering absorption coefficient of hydrogen (48.5 cm²/g) due to the scattering allows neutrons to reveal hydrocarbon structures with more contrast than X-rays, but at the same time limits the sample size and thickness that can be investigated. Many planar shaped objects, particularly wood samples, are sufficiently thin to allow thermal neutrons to transmit through the sample in a direction perpendicular to the planar face but not in a parallel direction, due to increased thickness. Often, this is an obstacle that prevents some tomographic reconstruction algorithms from obtaining desired results because of inadequate information or presence of distracting artifacts due to missing projections. This can be true for samples such as the distribution of glue in glulam (boards of wooden layers glued together), or the course of partially visible annual rings in trees where the features of interest are parallel to the planar surface of the sample. However, it should be possible to study these features by rotating the specimen within a limited angular range. In principle, this approach has been shown previously in a study with fast neutrons [2]. A study of this kind was performed at the Antares facility of FRM II in Garching with a 2.6×10⁷/cm² s thermal neutron beam. The limit of penetration was determined for a wooden step wedge carved from a 2 cm×4 cm block of wood in comparison to other materials such as heavy metals and Lucite as specimens rich in hydrogen. The depth of the steps was 1 cm, the height 0.5 cm. The annual ring structures were clearly detectable up to 2 cm thickness. Wooden specimens, i.e. shivers, from a sunken old ship have been subjected to tomography. Not visible from the outside, clear radial structures have been found that are typical for certain kinds of wood. This insight was impaired in a case where the specimen had been soaked with ethylene glycol. In another large sample study, a planar board made of glulam has been studied to show the glued layers. This study shows not only the limits of penetration in wood but also demonstrates access to structures perpendicular to the surface in larger planar objects by tomography with fast neutrons, even with incomplete sets of projection data that covers an angular range of only 90° or even 60°.     

A review of computerized tomography with application to two-phase flows

The technique of computerized tomography (Ct) has established itself as a leading tool in diagnostic radiology over the past twenty years and is catching on fast in the non-destructive evaluation area in a variety of situations. Ct instrumentation involves a source and a detector system to scan the object of interest. The source can be acoustic, microwave, X-ray, gamma-ray, etc. depending upon the type of material being investigated. For fluid-flows, gamma-rays are quite suitable. There are basically two types of data collection geometries — fan-beam and parallel beam. Fan-beam requires less number of sources as one source feeds several detectors arranged in a fan-beam. The use ofCt in multi-phase flow studies has been limited presently to only a few laboratory experiments and the results indicate thatCt does hold a lot of promise as an effective investigative methodology to understand some of the complex phenomena encountered in multi-phase flows. Some newCt algorithms developed specifically for pipe-flows have shown good results on some air-water flow data for a 15 cm dia pipe.     

一种基于模型的光学层析图像重建方法

光学层析图像重建是个病态问题,测量误差会在重建过程中被放大,对此,提出一种以广义高斯马尔可夫随机场模型为先验信息的光学层析图像重建方法.重建过程是对目标函数的优化过程,目标函数关于光学参数的梯度计算是算法中的难点,因此,提出一种基于梯度树的梯度计算方法.文中分别给出了吸收系数和散射系数的重建结果,并引入三个指标因子衡量重建图像的质量,进而列出不同重建算法下,重建图像的指标值.最后通过对重建结果和指标因子取值的比较,分析基于模型的重建算法的有效性.