锥束覆盖方法的并行实现及性能分析

三维螺旋锥束CT重建算法的快速实现是CT理论与实际应用中关注的焦点。本文基于锥束覆盖方法[1]对Katsevich精确反演公式设计了并行算法并给出了算法的并行性能分析。从本文的结果可以看出,该算法是解决三维螺旋锥束CT的重建算法时效性的一个可行途径。     

三维锥形束CT解析重建算法发展综述

同二维的扇束、平行束相比,三维锥束CT需要的扫描时间更短,可以获得更好的空间分辨率和更高的射线利用效率。虽然锥束CT的解析重建算法在数学计算上比较复杂,由于其运算量较大,工程实现起来也有一定的困难,但是随着近几年硬件和算法的快速发展,三维锥束CT变得越来越有希望,医用及工业CT正向着中等甚至大锥角三维锥束CT过渡。鉴于其巨大的实用背景,本文对近些年三维锥束解析重建算法的发展做了一个回顾,尤其是针对长物体问题的算法及短物体问题的算法进行的研究,并对各类算法作了比较和讨论,最后对三维锥形束CT解析重建算法理论的发展进行了展望。     

半像素错位技术在三维CT重建中的应用

本文介绍了一种基于半像素错位的多幅锥束投影数据重建高分辨率投影数据的技术,利用在水平和垂直方向上进行半像素错位的方法提高了锥束投影数据的分辨率,并给出了具体的实现方法,同时对重建后的投影数据用FDK方法进行重建,实验结果表明,重建出来的三维物体的质量在水平和垂直方向都获得了的提高,而且还有抑制噪声的效果。     

FDK算法中一种新的插值方法

针对在FDK算法的反投影过程中，各个体素在探测器上投影分布的特点，本文提出一种新的插值方法。该方法根据体素投影的特点，采用在重建过程中，根据其在不同扫描角度下在各个探测器单元上的投影所占面积的加权和作为反投影值。实际实验结果表明，在FDK算法中这个新的插值方法比传统的插值方法（如：最近邻插值，双线性插值）重建出来的图像边缘清晰，而且能更好地抑制噪声。     

基于平板探测器的锥束CT系统综述

锥束CT系统和二维扇束、平行束CT系统相比具有空间分辨率高、投影数据采集时间短、射线利用效率高等优点 ,但由于算法运算量大和工程实现上的困难以往一直没能在实际中应用 ,随着近几年硬件和算法的发展 ,锥束CT已经进入实用阶段 ,而平板探测器则是最适合锥束CT的探测器。本文对目前平板探测器锥束CT系统的发展状况做了综述 ,讨论了平板探测器用于锥束CT系统的优越性 ,对各种平板探测器锥束CT系统的几何结构和应用中的问题进行了比较和讨论 ,最后对平板探测器锥束CT未来的发展进行了展望。     

基于像素采样不足的伪迹处理方法

在实际的三维锥束CT重建中，受扫描结构的限制，当连续X射线穿过物体时，像素对射线的采样间隔不能满足Nyqust采样定理，这样通道信号产生混叠，使得重建图像出现伪迹。本论文针对这一问题，在用splatting算法计算代数重建算法权系数的基础上，分析了伪迹产生的原因并对对应的内插函数作了适当的变换，提出了适用于3-D锥束圆轨迹CT扫描系统的去伪处理方法。结果表明，经过去伪处理后，重建图像的分辨率明显提高。     

锥束/多层螺旋CT重建算法在工业CT中的应用及对运算速度的研究

目前临床应用的锥束/多层螺旋CT主要采用螺旋Feldkamp算法进行图像重建,体数据的重建需要消耗大量的时间,锥束/多层螺旋CT的图像重建一直是图像重建中的关键问题和衡量CT系统的重要指标之一。本文分析了几种快速重建算法的特点,并从算法结构、实现技巧及代码优化等方面论述了图像重建的方法,计算模拟和实验结果显示了这些方法可有效提高图像重建的速度。     

一种实用的基于GPU的Katsevich算法的实现

Katseivch算法是精确地解决锥束螺旋CT“长物体”问题的滤波反投影（FBP）形式的CT重建算法,不过它依然是非常耗时的,实际应用中必须考虑如何加速的问题。本文给出了一个使用通用显卡（GPU）对该算法进行并行加速的方法。同已有的方法相比较,几乎所有的计算都在GPU上完成,并且重建时所使用的积分范围是由PI线决定的,并且给出了算法所需要的精确地显存大小,10次数也被最大可能地降低。本文使用了标准数值模型对方法的速度、准确性和稳定性进行了验证。     

面向CT成像的深度重建算法研究进展

随着计算机断层扫描(Computed Tomography, CT)技术的发展与广泛应用,其重建算法得到了长足的发展。近年来,基于数据驱动的深度学习技术与CT图像重建结合的趋势愈加明显,深度学习应用于影像重建在实验环境中取得了显著的重建效果。本文以CT成像原理、重建技术发展以及存在问题为切入点。首先,围绕深度学习的有监督和无监督学习策略,将两类基于深度学习的重建算法原理与目前国内外研究进展进行结合介绍。主要包括有监督学习对传统解析迭代方法重建过程的网络实现与优化,以及无监督学习中自监督学习和生成模型类重建原理方法。其次,介绍了一些常用的基于像素、区域结构细节、语义特征等层面的损失函数,并对它们的优缺点进行了分析。最后,本文对深度重建领域仍存在的一些问题进行了总结,并介绍了一些新的学习型重建策略。     

基于光线投射的锥束CT正投影算法研究

计算机断层成像（computed tomography,CT）作为一种现代成像技术已经被广泛应用于医学诊断、工业无损检测等领域。在研究CT重建算法的过程中,正投影模拟数据是必不可少的一部分。本文提出一种基于光线投射算法的圆轨迹锥束扫描模式下的正投影算法,并结合CUDA（compute unified device architecture,统一计算设备架构）技术,实现了GPU（graphics processing unit,图形处理器）加速正投影计算。通过与传统的正投影算法相比,本文算法在投影图像质量上有一定的提高,并具有更高的计算效率。     

一种实用的二维工业CT重建算法

Computed tomography(CT)has already been inpractical use in many fields such as industrial non-de-structive testing and medical diagnosis.With industrialCTscanners,the inner structure especially flaws of va-rious devices can be non-invasively detected.Apracti-cal software have been developed to reconstruct thetwo-dimensional(2D)tomographic images from theraw data of industrial CT.The forward and inverseproblem of fan-beam CTimaging are studied in this ar-ticle.There are different reconstruc…     

Modern Tools for Modern Brachytherapy

This review aims to showcase the brachytherapy tools and technologies that have emerged during the last 10 years. Soft-tissue contrast using magnetic resonance and ultrasound imaging has seen enormous growth in use to plan all forms of brachytherapy. The era of image-guided brachytherapy has encouraged the development of advanced applicators and given rise to the growth of individualised 3D printing to achieve reproducible and predictable implants. These advances increase the quality of implants to better direct radiation to target volumes while sparing normal tissue. Applicator reconstruction has moved beyond manual digitising, to drag and drop of three-dimensional applicator models with embedded pre-defined source pathways, ready for auto-recognition and automation. The simplified TG-43 dose calculation formalism directly linked to reference air kerma rate of high-energy sources in the medium water remains clinically robust. Model-based dose calculation algorithms accounting for tissue heterogeneity and applicator material will advance the field of brachytherapy dosimetry to become more clinically accurate. Improved dose-optimising toolkits contribute to the real-time and adaptive planning portfolio that harmonises and expedites the entire image-guided brachytherapy process. Traditional planning strategies remain relevant to validate emerging technologies and should continue to be incorporated in practice, particularly for cervical cancer. Overall, technological developments need commissioning and validation to make the best use of the advanced features by understanding their strengths and limitations. Brachytherapy has become high-tech and modern by respecting tradition and remaining accessible to all.     

Incorporation of local dependent reliability information into the Prior Image Constrained Compressed Sensing (PICCS) reconstruction algorithm

PurposeThe reduction of dose in cone beam computer tomography (CBCT) arises from the decrease of the tube current for each projection as well as from the reduction of the number of projections. In order to maintain good image quality, sophisticated image reconstruction techniques are required. The Prior Image Constrained Compressed Sensing (PICCS) incorporates prior images into the reconstruction algorithm and outperforms the widespread used Feldkamp-Davis-Kress-algorithm (FDK) when the number of projections is reduced. However, prior images that contain major variations are not appropriately considered so far in PICCS. We therefore propose the partial-PICCS (pPICCS) algorithm. This framework is a problem-specific extension of PICCS and enables the incorporation of the reliability of the prior images additionally.Material and MethodsWe assumed that the prior images are composed of areas with large and small deviations. Accordingly, a weighting matrix considered the assigned areas in the objective function. We applied our algorithm to the problem of image reconstruction from few views by simulations with a computer phantom as well as on clinical CBCT projections from a head-and-neck case. All prior images contained large local variations. The reconstructed images were compared to the reconstruction results by the FDK-algorithm, by Compressed Sensing (CS) and by PICCS. To show the gain of image quality we compared image details with the reference image and used quantitative metrics (root-mean-square error (RMSE), contrast-to-noise-ratio (CNR)).ResultsThe pPICCS reconstruction framework yield images with substantially improved quality even when the number of projections was very small. The images contained less streaking, blurring and inaccurately reconstructed structures compared to the images reconstructed by FDK, CS and conventional PICCS. The increased image quality is also reflected in large RMSE differences.ConclusionsWe proposed a modification of the original PICCS algorithm. The pPICCS algorithm incorporates prior images as well as information about location dependent uncertainties of the prior images into the algorithm. The computer phantom and experimental data studies indicate the potential to lowering the radiation dose to the patient due to imaging while maintaining good image quality.     

Software-guided standardization of manual landmark data in medical images

It is crucial to evaluate registration algorithms in order to make them available in clinical practice. Several evaluation strategies have been proposed in the past, and one approach is to evaluate these algorithms with intrinsic anatomical landmarks identified by a health professional. The acquisition and handling of large amounts of these landmark data is a time-consuming task for the health professional, and it is vulnerable to errors and inconsistencies. Additionally, limited access to appropriate tools makes dealing with landmark data considerably more difficult.We introduce a strategy for the acquisition of landmarks for the landmark-based evaluation of registration algorithms and we present an ontology-driven software tool that assists the different partners involved to act according to that strategy. This tool provides the user with intrinsic knowledge of the registration problems, the possibility to conveniently make the acquired data available to further processing, and an easy-to-use graphical interface.     

另一种基于弦的锥束CT图像重建的推导方法

A series of papers by our group has layed thefoundation of a very general theory of image reconstruc-tion in cone-beam CT.Initially,Zou and Pan devel-oped a general formula from which a back-projectionfiltration algorithm was derived for yielding the imageon aπ-line segement of a helical source trajectory[1]with a minimum set of projection data.Theπ-line seg-ment is a line segment that connects two points on ahelix separated by no more than a single turn.It wasestablished previously thatπ…     

浸润性乳腺癌乳房切除术联合Ⅰ期重建后放疗相关问题研究现状

随着对外形美观的要求越来越高,越来越多患者在乳房切除术后会选择不同类型重建手术。对于这部分患者,怎样的综合治疗时序可以让患者在外形美观和抗肿瘤治疗疗效间取得平衡、得到最大获益,是目前多学科治疗关注的重要问题。本文从术后放疗对乳房重建的美容影响、组织扩张器和永久性假体置换与术后放疗的时序关系以及乳房重建手术和放疗技术的最新进展做一综述。笔者综合现有文献报道以及临床实践总结了重建手术与辅助治疗的整体决策推荐流程图,为临床实践提供参考。     

二维Renyi熵图像阈值选取快速递推算法

阈值分割是图像处理技术中的一个基本问题。阈值选取则是阈值分割技术的关键。随着阈值分割技术的不断发展，对阈值选取方法的准确性及快速性的要求越来越高。本文提出了二维Renyi熵阈值法的两种快速递推算法，消除了计算过程中的重复计算，大大提高了二维Renyi熵阈值选取算法的运行速度。通过对各种类型的图像进行大量实验，结果表明二维Renyi熵阈值选取算法分割准确，本文所提出的两种快速算法的运行时间几乎不到原始算法的0．1％，这使得二维Renyi熵法更具实用性。