Volume 20, Issue 10

A new iterative maximum-likelihood reconstruction algorithm for X-ray computed tomography is presented. The algorithm prevents beam hardening artifacts by incorporating a polychromatic acquisition model. The continuous spectrum of the X-ray tube is modeled as a number of discrete energies. The energy dependence of the attenuation is taken into account by decomposing the linear attenuation coefficient into a photoelectric component and a Compton scatter component. The relative weight of these components is constrained based on prior material assumptions. Excellent results are obtained for simulations and for phantom measurements. Beam-hardening artifacts are effectively eliminated. The relation with existing algorithms is discussed. The results confirm that improving the acquisition model assumed by the reconstruction algorithm results in reduced artifacts. Preliminary results indicate that metal artifact reduction is a very promising application for this new algorithm.

提出了一种用于X射线计算机断层扫描的新的迭代最大似然重建算法。该算法通过引入多色采集模型来防止射束硬化伪影。X射线管的连续频谱被建模为多个离散能量。衰减的能量依赖性通过将线性衰减系数分解为光电效应分量和康普顿散射分量来考虑。基于先前的材料假设，这些分量的相对权重受到约束。模拟和体模测量获得了优异的结果。射束硬化伪影被有效消除。讨论了与现有算法的关系。结果证实，改进重建算法假设的采集模型可减少伪影。初步结果表明，金属伪影减少是该新算法的一个非常有前景的应用。

Presents a new image-based technique to rigidly register intraoperative three-dimensional ultrasound (US) with preoperative magnetic resonance (MR) images. Automatic registration is achieved by maximization of a similarity measure which generalizes the correlation ratio, and whose novelty is to incorporate multivariate information from the MR data (intensity and gradient). In addition, the similar...

提出了一种新的基于图像的技术，用于将术中三维超声（US）与术前磁共振（MR）图像进行刚性配准。通过最大化一种推广了相关比的相似性度量来实现自动配准，其新颖之处在于整合了MR数据的多变量信息（强度和梯度）。此外，类似的...

To achieve the complete three-dimensional (3-D) data retrieval of the shape of dentition, dental casts were measured from four directions; occlusal, right, left, and labial sides using a line laser scanner. Reconstruction of the entire shape, including undercuts and tooth crowding area, was attempted by applying a perceptual grouping algorithm, which is one of pattern-recognition theories. In the ...

为获得牙列形状的完整三维数据，使用线激光扫描仪从四个方向（咬合面、右侧、左侧和唇侧）测量牙模。尝试应用感知分组算法（一种模式识别理论）重建包括倒凹区和牙齿拥挤区域的完整形状。在...

Component averaging (CAV) was recently introduced by Censor, Gordon, and Gordon as a new iterative parallel technique suitable for large and sparse unstructured systems of linear equations. Based on earlier work of Byrne and Censor, it uses diagonal weighting matrices, with pixel-related weights determined by the sparsity of the system matrix. CAV is inherently parallel (similar to the very slowly...

组件平均（CAV）最近由Censor、Gordon和Gordon引入，作为一种适用于大型稀疏无结构线性方程组的新迭代并行技术。基于Byrne和Censor的早期工作，它使用对角加权矩阵，其中像素相关权重由系统矩阵的稀疏性决定。CAV本质上具有并行性（类似于非常缓慢的...）

The maximum a posteriori (MAP) Bayesian iterative algorithm using priors that are gamma distributed, due to Lange, Bahn and Little, is extended to include parameter choices that fall outside the gamma distribution model. Special cases of the resulting iterative method include the expectation maximization maximum likelihood (EMML) method based on the Poisson model in emission tomography, as well as...

由Lange、Bahn和Little提出的基于伽马分布先验的最大后验（MAP）贝叶斯迭代算法被扩展，以包含伽马分布模型之外的参数选择。所得迭代方法的特例包括基于发射断层扫描中泊松模型的期望最大化最大似然（EMML）方法，以及...

A probabilistic deformable model for the representation of multiple brain structures is described. The statistically learned deformable model represents the relative location of different anatomical surfaces in brain magnetic resonance images (MRIs) and accommodates their significant variability across different individuals. The surfaces of each anatomical structure are parameterized by the amplit...

描述了一种用于表示多个脑结构的概率可变形模型。该统计学习的可变形模型表示了脑磁共振图像（MRI）中不同解剖表面的相对位置，并适应了不同个体间的显著变异性。每个解剖结构的表面通过振幅参数化...

The reconstruction of tomographic images is often treated as a linear deblurring problem. When a high-density, man-made metal object is present somewhere in the image field, it is a deblurring problem in which the unknown function has a component that is known except for some location and orientation parameters. The authors first address general linear deblurring problems in which a known function...

断层图像的重建通常被视为线性去模糊问题。当图像场中存在高密度的人造金属物体时，这是一个去模糊问题，其中未知函数有一个除了一些位置和方向参数外已知的分量。作者首先处理一般线性去模糊问题，其中已知函数...

Magnetic resonance imaging (MRI) offers potential advantages over conventional X-ray techniques for guiding and evaluating intravascular interventions. The development of methods to safely and robustly localize and track devices under MRI guidance is mandatory to enable automatic scan plane adaptation so as to exploit the three-dimensional imaging capabilities of the MRI scanner. With regard to th...

磁共振成像（MRI）在引导和评估血管内介入方面比传统X射线技术具有潜在优势。开发在MRI引导下安全且稳健地定位和追踪设备的方法，对于实现自动扫描平面适应以利用MRI扫描仪的三维成像能力至关重要。关于...

In this paper, a reliable method to reduce the noise from nuclear magnetic resonance (NMR) signals using a recently developed linear critically sampled time-frequency transform is proposed. In addition to its low computational requirements, this transform has many theoretical advantages that make it a good candidate for NMR signal enhancement. NMR signals in the transform domain are concentrated i...

本文提出了一种利用最近发展的线性临界采样时频变换来降低核磁共振（NMR）信号噪声的可靠方法。除了计算量低之外，该变换还具有许多理论优势，使其成为核磁共振信号增强的良好候选。NMR信号在变换域中集中……

Layer decomposition is a promising method for obtaining accurate densitometric profiles of diseased coronary artery segments. This method decomposes coronary angiographic image sequences into moving densitometric layers undergoing translation, rotation, and scaling. In order to evaluate the accuracy of this technique, the authors have developed a technique for embedding realistic simulated moving ...

层分解是一种有前景的方法，用于获取病变冠状动脉段的准确密度测量剖面。该方法将冠状动脉造影图像序列分解为经历平移、旋转和缩放的移动密度层。为了评估该技术的准确性，作者开发了一种嵌入逼真模拟移动...的技术

Describes a motion detection method specific to hybrid positron emission tomography/single photon emission computed tomography systems. The method relies on temporal fractionation of the acquisition into three data sets followed by an algorithm based on the cross correlation (CC) of partial sinograms from successive sets at different rotations of the camera. Spatial inconsistencies due to motion a...

描述了一种专门用于混合正电子发射断层扫描/单光子发射计算机断层扫描系统的运动检测方法。该方法依赖于将采集时间分成三个数据集，然后基于连续不同旋转角度下的部分正弦图的互相关算法。由于运动导致的空间不一致...