Volume 17, Issue 2

The solution of impedance distribution in electrical impedance tomography is a nonlinear inverse problem that requires the use of a regularization method. The generalized Tikhonov regularization methods have been popular in the solution of many inverse problems. The regularization matrices that are usually used with the Tikhonov method are more or less ad hoc and the implicit prior assumptions are, thus, in many cases inappropriate. In this paper, the authors propose an approach to the construction of the regularization matrix that conforms to the prior assumptions on the impedance distribution. The approach is based on the construction of an approximating subspace for the expected impedance distributions. It is shown by simulations that the reconstructions obtained with the proposed method are better than with two other schemes of the same type when the prior is compatible with the true object. On the other hand, when the prior is incompatible with the true object, the method will still give reasonable estimates.

电阻抗成像中阻抗分布的求解是一个非线性逆问题，需要使用正则化方法。广义Tikhonov正则化方法在许多逆问题的求解中很受欢迎。通常与Tikhonov方法一起使用的正则化矩阵或多或少是特设的，因此隐含的先验假设在许多情况下是不合适的。在本文中，作者提出了一种构建与阻抗分布先验假设相一致的正则化矩阵的方法。该方法基于为预期的阻抗分布构建近似子空间。模拟结果表明，当先验与真实对象一致时，所提出的方法获得的重建结果优于其他两种同类方案。另一方面，当先验与真实对象不一致时，该方法仍能给出合理的估计。

A system that automatically segments and labels glioblastoma-multiforme tumors in magnetic resonance images (MRIs) of the human brain is presented. The MRIs consist of T1-weighted, proton density, and T2-weighted feature images and are processed by a system which integrates knowledge-based (KB) techniques with multispectral analysis. Initial segmentation is performed by an unsupervised clustering ...

介绍了一个自动分割和标记人脑磁共振图像（MRI）中胶质母细胞瘤的系统。MRI由T1加权、质子密度和T2加权特征图像组成，通过集成基于知识（KB）技术与多光谱分析的系统进行处理。初始分割通过无监督聚类进行...

Using a theory of list-mode maximum-likelihood (ML) source reconstruction presented recently by Barrett et al. (1997), this paper formulates a corresponding expectation-maximization (EM) algorithm, as well as a method for estimating noise properties at the ML estimate. List-mode ML is of interest in cases where the dimensionality of the measurement space impedes a binning of the measurement data. ...

本文利用Barrett等人（1997）近期提出的列表模式最大似然（ML）源重建理论，制定了相应的期望最大化（EM）算法，以及ML估计下噪声特性的估计方法。列表模式ML在测量空间维数阻碍测量数据分箱的情况下具有重要意义。

In this paper the authors present a new unsupervised fuzzy algorithm for vessel tracking that is applied to the detection of the ocular fundus vessels. The proposed method overcomes the problems of initialization and vessel profile modeling that are encountered in the literature and automatically tracks fundus vessels using linguistic descriptions like "vessel" and "nonvessel." The main tool for d...

本文作者提出了一种新的无监督模糊血管跟踪算法，用于检测眼底血管。该方法克服了文献中遇到的初始化和血管轮廓建模问题，并使用“血管”和“非血管”等语言描述自动跟踪眼底血管。主要工具是...

This paper presents a method for segmentation and tracking of cardiac structures in ultrasound image sequences. The developed algorithm is based on the active contour framework. This approach requires initial placement of the contour close to the desired position in the image, usually an object outline. Best contour shape and position are then calculated, assuming that at this configuration a glob...

本文提出了一种在超声图像序列中对心脏结构进行分割与跟踪的方法。所开发的算法基于主动轮廓框架。该方法需要将轮廓初始放置在图像中接近目标位置（通常是物体轮廓）处。然后计算最佳轮廓形状和位置，假设在该配置下，能量泛函达到全局最小值。

Grayscale inhomogeneities in magnetic resonance (MR) images confound quantitative analysis of these images. Homomorphic unsharp masking and its variations have been commonly used as a post-processing method to remove inhomogeneities in MR images, However, little data is available in the literature assessing the relative effectiveness of these algorithms to remove inhomogeneities, or describing how...

磁共振（MR）图像中的灰度不均匀性会干扰这些图像的定量分析。同态反锐化掩膜及其变体常被用作后处理方法以消除MR图像中的不均匀性，然而，文献中关于评估这些算法在消除不均匀性方面的相对有效性，或描述如何……的数据很少。

The use of the wavelet transform is explored for the detection of differences between brain functional magnetic resonance images (fMRIs) acquired under two different experimental conditions. The method benefits from the fact that a smooth and spatially localized signal can be represented by a small set of localized wavelet coefficients, while the power of white noise is uniformly spread throughout...

探索使用小波变换来检测在两种不同实验条件下获取的脑功能磁共振图像（fMRIs）之间的差异。该方法得益于这样一个事实：平滑且空间局部化的信号可以用少量局部小波系数表示，而白噪声的功率均匀分布在整个...

Gastrointestinal (GI) tract examination with spiral/helical computed tomography (CT) is currently performed by slice-based inspection of axial images. CT colography is a recent advance which allows an intraluminal visualization of the colon, similar to endoscopy. Various rendering algorithms have been developed with promising results, however navigation through the complex, tortuous anatomy of the...

目前，螺旋/螺旋计算机断层扫描（CT）检查胃肠道是通过逐层检查轴向图像进行的。CT结肠成像是一项最新进展，它允许像内窥镜检查一样对结肠进行腔内可视化。已经开发了各种渲染算法，并取得了有希望的结果，然而在复杂、曲折的解剖结构中导航……

Presents two new methods for robust parameter estimation of mixtures in the context of magnetic resonance (MR) data segmentation. The head is constituted of different types of tissue that can be modeled by a finite mixture of multivariate Gaussian distributions. The authors' goal is to estimate accurately the statistics of desired tissues in presence of other ones of lesser interest. These latter ...

针对磁共振（MR）数据分割中的混合模型，提出了两种新的鲁棒参数估计方法。头部由不同类型的组织构成，这些组织可以用多元高斯分布的有限混合来建模。作者的目标是在存在其他不太感兴趣的组织的情况下，准确估计所需组织的统计量。这些后者……

Cochlear implantation is the standard treatment for profound hearing loss, Preimplantation and postimplantation spiral computed tomography (CT) is essential in several key clinical and research aspects. The maximum image resolution with commercial spiral CT scanners is insufficient to define clearly anatomical features and implant electrode positions in the inner ear, In this paper, the authors de...

人工耳蜗植入是治疗重度听力损失的标准方法，术前和术后螺旋计算机断层扫描（CT）在多个关键的临床和研究方面至关重要。商用螺旋CT扫描仪的最大图像分辨率不足以清晰定义内耳的解剖结构和植入电极位置。在本文中，作者...

In this paper, the authors developed and tested strategies for estimating myocardial blood flow (MBF) and generating MBF parametric images using positron emission tomography (PET), N-13 ammonia, and the generalized linear least square (GLLS) method. GLLS was generalized to the general linear compartment model, modified for the correction of spillover, validated using simulated N-13 ammonia data, a...

本文作者开发并测试了使用正电子发射断层扫描（PET）、N-13氨和广义线性最小二乘（GLLS）方法估计心肌血流量（MBF）并生成MBF参数图像的策略。GLLS被推广到一般线性房室模型，并进行了修正以校正溢出效应，使用模拟的N-13氨数据进行了验证...

This paper demonstrates a time-saving, automated method that helps to segment the lateral ventricles and caudate nucleus in T1-weighted coronal magnetic resonance (MR) brain images of normal control subjects. The method involves choosing intensity thresholds by using anatomical information and by locating peaks in histograms. To validate the method, the lateral ventricles and caudate nucleus were ...

本文展示了一种省时、自动化的方法，有助于在正常对照受试者的T1加权冠状磁共振（MR）脑图像中分割侧脑室和尾状核。该方法通过利用解剖信息和定位直方图中的峰值来选择强度阈值。为了验证该方法，侧脑室和尾状核被...

The radial derivative of the three-dimensional (3-D) radon transform of an object is an important intermediate result in many analytically exact cone-beam reconstruction algorithms. The authors briefly review Grangeat's (1991) approach for calculating radon derivative data from cone-beam projections and then present a new, efficient method for 3-D radon inversion, i.e., reconstruction of the image...

物体的三维Radon变换的径向导数是许多解析精确锥束重建算法中的重要中间结果。作者简要回顾了Grangeat（1991）从锥束投影计算Radon导数数据的方法，然后提出了一种新的、高效的三维Radon反演方法，即图像重建...

Scatter and spatial resolution effects degrade the accuracy of radioactivity concentration estimates obtained from positron emission tomography (PET) data. The authors present and evaluate a methodology for region quantification which accounts for these degradations. The method is based on analysis of sinogram data and does not require dynamic data sequences to be reconstructed. Moreover, estimate...

散射和空间分辨率效应降低了从正电子发射断层扫描（PET）数据获得的放射性浓度估计的准确性。作者提出并评估了一种考虑这些降质的区域量化方法。该方法基于正弦图数据分析，不需要重建动态数据序列。此外，估计...

Maps of spin lattice relaxation time (T/sub 1/) can be reconstructed directly from magnetic resonance imaging (MRI) k-space data measured with very short data acquisition times, e.g., a data set for a 128/spl times/128 T/sub 1/ map can be acquired in less than 3 s using gradients with 10-T/m/s slew rate. In principle, this approach could be extended to quantitate other MRI parameters but current u...

自旋-晶格弛豫时间（T1）图可以直接从磁共振成像（MRI）k空间数据中重建，这些数据以极短的数据采集时间测量，例如，使用10-T/m/s的梯度转换速率，可以在不到3秒内获得128×128的T1图数据集。原则上，这种方法可以扩展到量化其他MRI参数，但当前……

An improved algorithm for planar rotational motion artifact suppression in standard two-dimensional Fourier transform magnetic resonance images is presented. It is shown that interpolation of acquired view data on the uncorrupted k-space create data overlap and void regions. The authors present a method of managing overlap data regions, using weighted averaging of redundant data. The weights are a...

提出了一种改进的算法，用于抑制标准二维傅里叶变换磁共振图像中的平面旋转运动伪影。研究表明，对未受损k空间中的采集视图数据进行插值会导致数据重叠和空白区域。作者提出了一种管理重叠数据区域的方法，使用冗余数据的加权平均。权重是...

Accurate quantitation of small lesions with positron emission tomography (PET) requires correction for the partial volume effect. Traditional methods that use Gaussian models of the PET system were found to be insufficient. A new approach that models the non-Gaussian object-dependent scatter was developed. The model consists of eight simple functions with a total of 24 parameters. Images of line a...

使用正电子发射断层扫描（PET）对小病灶进行精确量化需要校正部分体积效应。传统方法使用PET系统的高斯模型被发现不足。开发了一种新的方法来模拟非高斯对象相关的散射。该模型由八个简单函数组成，共24个参数。线成像...

Two forms of a sampling theorem for concentric circles are established for a bandlimited two-dimensional (2-D) function. The location of the samples is prescribed either on equidistant circles or on the roots of the Bessel function J/sub 0/(). Both methods give comparable results, however, the number of samples required for their numerical evaluation is significantly less for the root-sampling for...

针对带限二维函数，建立了两种形式的同心圆采样定理。样本的位置要么规定在等距圆上，要么规定在贝塞尔函数 J/sub 0/() 的根上。两种方法给出了可比较的结果，然而，对于数值评估所需的样本数量，根采样方法显著较少...

A method for determining whether structures distributed along a cell's membrane represent a random spatial distribution is presented in this paper. Two three-dimensional (3-D) images are acquired from one cell by wide-field digital imaging of cells which have been labeled with two different fluorescent antibodies. Prior to spatial analysis, a constrained regularized least squares restoration of th...

本文提出了一种确定细胞膜上分布的结构是否代表随机空间分布的方法。通过对标记有两种不同荧光抗体的细胞进行宽场数字成像，获取同一个细胞的两幅三维图像。在进行空间分析之前，采用约束正则化最小二乘恢复...

On March 25, 1998, the scientific community unexpectedly lost a remarkable and most productive colleague. Urs E. Ruttimann, Ph.D., was one of that rare breed of individuals who makes solid and noteworthy contributions with little fuss and fanfare. His life and works are briefly reviewed.

1998年3月25日，科学界意外失去了一位杰出且最多产的同事。乌尔斯·E·鲁蒂曼博士是那种罕有的、默默无闻却做出扎实显著贡献的人。本文简要回顾了他的一生和工作。