Volume 24, Issue 1

The forward electroencephalography (EEG) problem involves finding a potential V from the Poisson equation /spl nabla//spl middot/(/spl sigma//spl nabla/V)=f, in which f represents electrical sources in the brain, and /spl sigma/ the conductivity of the head tissues. In the piecewise constant conductivity head model, this can be accomplished by the boundary element method (BEM) using a suitable integral formulation. Most previous work uses the same integral formulation, corresponding to a double-layer potential. We present a conceptual framework based on a well-known theorem (Theorem 1) that characterizes harmonic functions defined on the complement of a bounded smooth surface. This theorem says that such harmonic functions are completely defined by their values and those of their normal derivatives on this surface. It allows us to cast the previous BEM approaches in a unified setting and to develop two new approaches corresponding to different ways of exploiting the same theorem. Specifically, we first present a dual approach which involves a single-layer potential. Then, we propose a symmetric formulation, which combines single- and double-layer potentials, and which is new to the field of EEG, although it has been applied to other problems in electromagnetism. The three methods have been evaluated numerically using a spherical geometry with known analytical solution, and the symmetric formulation achieves a significantly higher accuracy than the alternative methods. Additionally, we present results with realistically shaped meshes. Beside providing a better understanding of the foundations of BEM methods, our approach appears to lead also to more efficient algorithms.

前向脑电图问题涉及从泊松方程∇·(σ∇V)=f中求解电位V，其中f代表脑内的电源，σ代表头部组织的电导率。在分段恒定电导率头部模型中，可以通过边界元法使用合适的积分公式来实现。以往的大多数工作使用相同的积分公式，对应于双层电位。我们提出了一个基于一个著名定理（定理1）的概念框架，该定理描述了定义在有界光滑曲面补集上的调和函数的特征。该定理指出，这些调和函数完全由它们在曲面上的值及其法向导数的值确定。它使我们能够将先前的边界元方法统一在一个框架中，并开发出两种利用该定理的新方法。具体地，我们首先提出了一种涉及单层电位的对偶方法。然后，我们提出了一种对称公式，它结合了单层和双层电位，这对脑电图领域来说是新颖的，尽管它已应用于电磁学中的其他问题。使用已知解析解的球形几何体对这三种方法进行了数值评估，对称公式的精度显著高于其他方法。此外，我们展示了使用真实形状网格的结果。除了更好地理解边界元方法的基础外，我们的方法似乎也导致了更高效的算法。

This work presents a novel texture and shape priors based method for kidney segmentation in ultrasound (US) images. Texture features are extracted by applying a bank of Gabor filters on test images through a two-sided convolution strategy. The texture model is constructed via estimating the parameters of a set of mixtures of half-planed Gaussians using the expectation-maximization method. Through ...

本文提出了一种基于纹理和形状先验的新方法，用于超声图像中的肾脏分割。通过采用双边卷积策略，在测试图像上应用一组Gabor滤波器来提取纹理特征。纹理模型通过使用期望最大化方法估计一组半平面高斯混合的参数来构建。通过...

This paper describes a flexible new methodology for accurate cone beam reconstruction with source positions on a curve (or set of curves). The inversion formulas employed by this methodology are based on first backprojecting a simple derivative in the projection space and then applying a Hilbert transform inversion in the image space. The local nature of the projection space filtering distinguishe...

本文描述了一种灵活的新方法，用于在源位置位于曲线（或曲线集）上时进行精确的锥束重建。该方法采用的逆公式首先在投影空间中对简单导数进行反投影，然后在图像空间中应用希尔伯特变换逆。投影空间滤波的局部特性使其区别于...

Mixture models are often used in the statistical segmentation of medical images. For example, they can be used for the segmentation of structural images into different matter types or of functional statistical parametric maps (SPMs) into activations and nonactivations. Nonspatial mixture models segment using models of just the histogram of intensity values. Spatial mixture models have also been de...

混合模型常用于医学图像的统计分割。例如，它们可用于将结构图像分割为不同物质类型，或将功能统计参数图(SPM)分割为激活和非激活区域。非空间混合模型仅基于强度值的直方图进行分割。空间混合模型也有...

The finite frequency bandwidth of ultrasound transducers and the nonnegligible width of transmitted acoustic beams are the most significant factors that limit the resolution of medical ultrasound imaging. Consequently, in order to recover diagnostically important image details, obscured due to the resolution limitations, an image restoration procedure should be applied. The present study addresses...

超声换能器的有限频率带宽和发射声束不可忽略的宽度是限制医学超声成像分辨率的最重要因素。因此，为了恢复由于分辨率限制而模糊的诊断重要图像细节，应采用图像复原程序。本研究涉及...

We present a statistically principled sinogram smoothing approach for X-ray computed tomography (CT) with the intent of reducing noise-induced streak artifacts. These artifacts arise in CT when some subset of the transmission measurements capture relatively few photons because of high attenuation along the measurement lines. Attempts to reduce these artifacts have focused on the use of adaptive fi...

我们提出了一种统计原理的正弦图平滑方法，用于X射线计算机断层扫描（CT），旨在减少噪声引起的条纹伪影。这些伪影出现在CT中，当传输测量的某个子集由于沿测量线的高衰减而捕获相对较少的光子时。减少这些伪影的尝试集中在使用自适应滤波器...

A three-dimensional image registration method for motion correction of functional magnetic resonance imaging (fMRI) time-series, based on independent component analysis (ICA), is described. We argue that movement during fMRI data acquisition results in a simultaneous increase in the joint entropy of the observed time-series and a decrease in the joint entropy of a nonlinear function of the derived...

描述了一种基于独立成分分析（ICA）的三维图像配准方法，用于功能性磁共振成像（fMRI）时间序列的运动校正。我们认为，fMRI数据采集过程中的运动会导致观测时间序列的联合熵同时增加，以及推导出的非线性函数的联合熵减少……

In Soares et al. (2000), the ensemble statistical properties of the rescaled block-iterative expectation-maximization (RBI-EM) reconstruction algorithm and rescaled block-iterative simultaneous multiplicative algebraic reconstruction technique (RBI-SMART) were derived. Included in this analysis were the special cases of RBI-EM, maximum-likelihood EM (ML-EM) and ordered-subset EM (OS-EM), and the s...

在Soares等人（2000年）的研究中，推导了重新缩放块迭代期望最大化（RBI-EM）重建算法和重新缩放块迭代同步乘法代数重建技术（RBI-SMART）的集合统计特性。该分析包括了RBI-EM、最大似然EM（ML-EM）和有序子集EM（OS-EM）的特例，以及...

While multislice spiral computed tomography (CT) scanners are provided by all major manufacturers, their specific interpolation algorithms have been rarely evaluated. Because the results published so far relate to distinct particular cases and differ significantly, there are contradictory recommendations about the choice of pitch in clinical practice. We present a new tool for the evaluation of mu...

虽然所有主要制造商都提供多层螺旋计算机断层扫描（CT）扫描仪，但它们的特定插值算法很少被评估。由于迄今为止发表的结果涉及不同的特定案例且差异显著，因此在临床实践中关于螺距的选择存在矛盾的建议。我们提出了一种新的工具来评估多层CT插值算法...

A non-Gaussian smoothing (NGS) technique is developed for filtering low count transmission (TR) data to be used for attenuation correction (AC) of positron emission tomography (PET) studies. The method is based on a statistical technique known as the generalized linear mixed model that allows an inverse link function that avoids the inversion of the observed transmission data. The NGS technique ha...

开发了一种非高斯平滑（NGS）技术，用于滤波用于正电子发射断层扫描（PET）研究的衰减校正（AC）的低计数透射（TR）数据。该方法基于称为广义线性混合模型的统计技术，该模型允许使用逆链接函数，避免对观测到的透射数据进行反演。NGS技术具有...

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