工业CT散射校正方法的研究

在工业CT的扫描重建过程中，散射效应使得重建图像出现模糊，各点灰度值同实际物体的吸收系数之间出现偏差，需要进行校正。如果采用一般的卷积方法，则需要迭代多次才能收敛，所以在校正时间上不能达到要求。采用一种结合散射模型的Ordered Subsets Convex方法对散射效果进行校正，在校正速度和质量上都得到了很好的结果。     

闪光层析成像散射修正计算研究

利用闪光照相成像系统底片信息,通过直接法对客体线性吸收系数空间分布进行重建,需能精确得到底片直穿量的信息,为解决这一问题必需对散射量进行修正。本文通过解析法推导出精确计算X光正向输运过程中未经碰撞与只经1次碰撞到达探测器处计数的理论公式,同时通过蒙特卡罗计算程序MCNP分析不同照相客体次级散射效应特性,对次级散射量进行数值修正,并由此编制快速光子正向计算程序SAT。与MCNP程序统计结果进行数值校验,结果表明,SAT程序能精确计算X光穿过照相客体到达探测器处的直穿量、散射量及总照射量计数,且计算速度远快于MCNP程序,这为闪光层析成像图像重建迭代扣除散射提供了快速精确的散射修正工具。     

凸度测量中的散射校正研究

本文分别从被测钢板的宽度、厚度和射线能量等3个方面对散射的影响进行了研究。首先建立凸度测量系统的蒙特卡罗模拟计算简化模型,分析了单能情况下钢板宽度和厚度对散射因子(SPR)的影响;然后建立X光机能谱计算仿真模型,模拟出给定管电压下X光机输出射线的连续能谱,并提出用多个单能分段等效的方法来代替连续能谱,模拟在实际连续能谱情况下钢板散射分布的规律,其模拟结果与实验测量结果能较好地吻合。     

一种CT成像散射抑制方法

在X射线CT(Computed Tomography)成像尤其是锥束成像过程中,散射是不可忽略的影响因素。探测信号中散射信号的存在导致CT图像中的伪影。依据散射信号的特征属性,提出了一种散射的估计方法。该方法利用简单的解析公式估计散射,简单易操作。实际的实验数据验证了方法的有效性。     

氢化锆中氢的散射律和散射矩阵研究

从氢化锆晶体散射律的角度出发，研究了氢化锆晶体散射的特殊机理。根据氢化锆晶体散射的声学模型和光学模型给出的频谱分布，用国际通用程序ＧＡＳＫＥＴ计算了氢化锆中氢的散射律。     

450keV锥束CT系统的散射校正研究

在450keV锥束工业CT成像系统中,对投影数据进行适当的散射校正是一步重要的数据校正.结合国内外散射校正方法研究的现状,对一种用散射校正板来进行散射校正方法的原理和实现进行了深入的研究.实验结果表明,这种校正方法能够对450KeV锥束CT成像系统进行有效地散射校正.     

192Ir CT箱包安检系统中射线的能量硬化和散射

本工作对¹⁹²IrCT箱包安检系统的射线能量硬化和散射进行实际测量和Monte-Carlo模拟计算，对该系统的能量硬化和散射影响予以定量分析，并提供CT图像重建校正的依据和方法。测量与计算结果表明，射线在吸收体中能量硬化的影响大于散射的影响。     

X射线工业CT散射修正

X射线工业CT（ICT）依赖准直器压低散射光子存在实际困难和不足。为解决这一问题，需采用相应的修正软件加以校正。文章从理想的模型出发，近似推导透射式ICT中散射X光子的理论计算公式，并把计算结果与实验结果进行比较。比较结果表明，两者吻合较好。据此，文章给出了散射光子软件修正的可行性方案。      

非对称散射核法去除锥形束CT计算机图像散射伪影

为去除锥形束CT计算机图像散射伪影,提出一种基于非对称笔形束核的散射反卷积去除算法,该算法采用MC模拟获取适应CT几何结构下的笔形束散射非对称数据,利用线性拟合算法对非对称核进行建模和拟合,通过计算机GPU实现基于拟合非对称散射核的快速运算从而实现快速的CT图像散射伪影校正。实验结果表明:该方法可以在5s内实现图像非一致性从15%下降至5%以下,该方法可以适用于临床应用。     

常波长和飞行时间模式下中子散射的散射矢量分辨率分析

讨论了中子散射实验中散射矢量分辨率问题，并根据目前谱仪通常的角度分辨和波长分辨参数，给出了常波长模式和飞行时间模式的分辨率曲线，并比较了不同模式的优缺点。分析表明，对于低q范围（〈0．4nm^-1）散射实验测量，飞行时间模式的分辨率更好；对于高q范围的中子散射测量，常波长模式更适合。     

Evaluation of the effect of scatter correction on lesion detectionin hepatic SPECT imaging

The effect of scatter correction on the accuracy of lesion detection in single-photon emission computed tomography (SPECT) imaging requires analysis of observer performance. Experiments were designed to evaluate the class of correction methods that subtract counts. Simulations were used to approximate liver imaging with labeled antibodies. The lesion was a 2.5-cm-diameter, spherical, “cold” tumor. Ramp-filtered backprojection and noniterative Chang attenuation compensation were used to approximate clinical practice. Perfect scatter rejection, defined as images containing only primary (nonscattered) photons, was selected as the ideal case. These images were compared with uncorrected images for conditions of both low- and high-scatter fractions (SF). The dual photopeak window (DPW) method was also tested to evaluate a practical subtraction correction. Receiver operating characteristic (ROC) experiments were conducted under signal-known-exactly (SKE) conditions, using the area under the curve as the index of accuracy. A statistically significant difference in detection was found only in a few experiments when scatter rejection was compared with no correction. The results suggest that scatter correction does not necessarily assure improved detection accuracy at a statistically significant level. However, corrections that produce conditions similar to ideal scatter rejection may offer such improvement in detection, particularly for cases of high SF's     

A semi-empirical model for a 90Sr beta-particle transmission thickness gauge for aluminum alloys

A semi-empirical model is derived and tested for a ⁹⁰Sr beta-particle transmission thickness gauge for aluminum alloys. Monte Carlo simulation is also used to verify the forward scatter part of the model. The model accurately accounts for thickness as well as forward scatter, gamma-ray background, and the measurement interference of sample density and composition. The model parameters are obtained and the model is benchmarked with industrial experimental data from a ⁹⁰Sr(⁹⁰Y) gauge.     

X取样方法的研究和应用(二)——一种适合于X取样的新散射校正方法

粉末样品测量和锡、铜、钼矿的X取样实践证实,本文建立的散射校正模型校正效果优于一般持/散法,所提供的地质品位的准确度不低于刻槽取样法,能满足生产要求。     

Filter-based energy-resolved X-ray computed tomography with a clinical imager

Filter-based energy-resolved X-ray computed tomography (CT) is an approach for implementing energy-resolved CT imaging using a flat-panel-detector-based cone-beam system. In this study, we performed experiments with a 20-cm-diameter phantom on a clinical X-ray imager. The material density results showed good agreement with the ideal values. We also propose an improved method for obtaining the detector response function and the X-ray spectrum, which requires fewer measurements and will be practical for future clinical use. Issues such as scatter and image noise remain to be addressed.     

On the Sensitivity and Application Possibilities of a Novel Compton Scatter Imaging System

A novel type of Compton scatter imaging system is described having the following features: maximum possible use is made of the available scatter radiation; and mechanical constraints permit millisecond 2-D scan times. The sensitivity of this type of scatter system is compared with that of transmission radiography, and it is found that the former is to be preferred for `radiologically thin' objects. An important medical example is the imaging in back scatter mode of radiation-sensitive organs lying near the surface of the body. Some industrial applications of the scatter technique also suggest themselves: e.g. for section imaging of `thin' sheets, plastic components, or back scatter imaging of surface regions of bulky objects, for which the conventional transmission technique gives inadequate penetration. Data correction for attenuation effects and multiple scatter radiation is illustrated using scatter images of objects drawn from the fields of medical and industrial radiology.     

A beam stop based correction procedure for high spatial frequency scatter in industrial cone-beam X-ray CT

In the energy range of industrial cone-beam CT (a 450 kV X-ray tube is used), the detector scatter (veiling glare) turned out to be the most important source of secondary radiation for a digital imaging system working in the indirect conversion mode. It has been shown that the detector scatter drives the shape of the total image scatter. As a consequence, the latter may be characterized by an important high spatial frequency content questioning the hypothesis, frequently invoked in the scatter correction techniques, of a slowly varying scatter. We propose a beam stop array (BSA) based method for the evaluation/subtraction of the image scatter. The technique has the potential of simultaneously manage all sources of scattering radiation. It can be used in the high spatial frequency scatter case at the condition of opportunely selecting the BSA effective sampling step. It has been shown that the BSA approach can be also successfully combined with a beam hardening correction scheme based on the linearisation method. The work we present is supported by experimental measurements performed with two test objects at two different beam qualities: (i) 200 kV + 2.5 mm of Cu and (ii) 400 kV + 4 mm of Pb and 1 mm of Cd. The detector scatter represents about 36% and 65% of the total white field image for the two investigated beam qualities, respectively.     

Scatter correction techniques in 3D PET: a Monte Carlo evaluation

In this work, a Monte Carlo software package, PET-EGS, designed to simulate realistic PET clinical studies, was used to assess three different approaches to scatter correction in 3D PET: analytical (gaussian fitting technique), experimental (dual energy window technique) and probabilistic (Monte Carlo technique). Phantom and clinical studies were carried out by 3D PET and simulated by PET-EGS. A clinical study (¹⁸F-FDG brain study) was simulated assuming PET emission/transmission multiple-volume images as a voxelised source object describing the distribution of both the radioactivity and attenuation coefficients and accounting for out-of-field activity and media. The accuracy of PET-EGS in modelling the physical response of a 3D PET scanner was assessed by statistical comparison between measured and total (scatter+unscatter) simulated distributions (probability for the two distributions to be the same distribution: p>0.95). The accuracy of the scatter models, for each scatter correction technique, was evaluated on sinograms by statistical comparison between the estimated and the simulated scatter distributions (agreement <1 σ). The accuracy of scatter correction was evaluated on sinograms by comparison between scatter corrected and simulated unscatter distributions, proving a comparable accuracy of all the considered scatter correction techniques for brainlike distributed sources     

焊接接头疲劳裂纹随机扩展的概率模型

焊接接头微观组织的不均匀性，使得结构疲劳裂纹萌生和扩展寿命的随机性很大。本文采用概率断裂力学方法和可靠性分析方法，针对压力容器焊接接头的组织不均匀特点，研究了焊缝区疲劳失效概率模型。Monte-Carlo数值模拟结果表明，这一模型对裂纹亚临界扩展规律的描述是令人满意的，在安全判定上是安定的。     

非晶硅电子射野影像装置的性能研究

使用DVS(Dosimetric verifying system)软件实现对非晶硅平板探测器的影像采集,通过分析不同辐照条件下得到的射野影像的像素值,研究非晶硅电子射野影像装置(Amorphous silicon electronic portal Imagingdevice,a-Si EPID)的辐射稳定性、剂量响应线性、照射野大小的散射影响以及不同帧时间、不同电容大小等参数设置对EPID读出信号值的影响。结果显示EPID在短期内显示出极好的稳定性,伪影增加了EPID的响应信号,减少两次照射的间隔时间或者增加两次照射剂量比例可使伪影变得更加明显。a-Si EPID具有良好的剂量线性关系,随着射野的增加散射因子也随着增加。因此只要经过适当的散射修正和剂量刻度,EPID可以作为剂量仪用来显示二维剂量分布。