Volume 16, Issue 2

A new approach to the problem of multimodality medical image registration is proposed, using a basic concept from information theory, mutual information (MI), or relative entropy, as a new matching criterion. The method presented in this paper applies MI to measure the statistical dependence or information redundancy between the image intensities of corresponding voxels in both images, which is assumed to be maximal if the images are geometrically aligned. Maximization of MI is a very general and powerful criterion, because no assumptions are made regarding the nature of this dependence and no limiting constraints are imposed on the image content of the modalities involved. The accuracy of the MI criterion is validated for rigid body registration of computed tomography (CT), magnetic resonance (MR), and photon emission tomography (PET) images by comparison with the stereotactic registration solution, while robustness is evaluated with respect to implementation issues, such as interpolation and optimization, and image content, including partial overlap and image degradation. Our results demonstrate that subvoxel accuracy with respect to the stereotactic reference solution can be achieved completely automatically and without any prior segmentation, feature extraction, or other preprocessing steps which makes this method very well suited for clinical applications.

提出了一种解决多模态医学图像配准问题的新方法，该方法使用信息论中的基本概念——互信息（MI）或相对熵作为新的匹配准则。本文提出的方法应用互信息来测量两幅图像中对应体素图像强度之间的统计依赖性或信息冗余，并假设当图像几何对齐时互信息最大。互信息最大化是一个非常通用且强大的准则，因为未对该依赖关系的性质做任何假设，也未对所涉及模态的图像内容施加限制性约束。通过与立体定向配准解决方案的比较，验证了互信息准则在计算机断层扫描（CT）、磁共振（MR）和光子发射断层扫描（PET）图像刚体配准中的准确性，同时评估了其对于实现问题（如插值和优化）和图像内容（包括部分重叠和图像退化）的鲁棒性。结果表明，可以完全自动地实现相对于立体定向参考解的亚体素精度，且无需任何预先分割、特征提取或其他预处理步骤，这使得该方法非常适合临床应用。

This paper presents two new rebinning algorithms for the reconstruction of three-dimensional (3-D) positron emission tomography (PET) data. A rebinning algorithm is one that first sorts the 3-D data into an ordinary two-dimensional (2-D) data set containing one sinogram for each transaxial slice to be reconstructed; the 3-D image is then recovered by applying to each slice a 2-D reconstruction method such as filtered-backprojection. This approach allows a significant speedup of 3-D reconstruction, which is particularly useful for applications involving dynamic acquisitions or whole-body imaging. The first new algorithm is obtained by discretizing an exact analytical inversion formula. The second algorithm, called the Fourier rebinning algorithm (FORE), is approximate but allows an efficient implementation based on taking 2-D Fourier transforms of the data. This second algorithm was implemented and applied to data acquired with the new generation of PET systems and also to simulated data for a scanner with an 18/spl deg/ axial aperture. The reconstructed images were compared to those obtained with the 3-D reprojection algorithm (3DRP) which is the standard "exact" 3-D filtered-backprojection method. Results demonstrate that FORE provides a reliable alternative to 3DRP, while at the same time achieving an order of magnitude reduction in processing time.

本文提出了两种新的重排算法，用于重建三维正电子发射断层扫描（PET）数据。重排算法首先将三维数据排序为普通二维数据集，其中包含每个待重建的横向切片的正弦图；然后通过对每个切片应用二维重建方法恢复三维图像...

A statistical model is presented that represents the distributions of major tissue classes in single-channel magnetic resonance (MR) cerebral images. Using the model, cerebral images are segmented into gray matter, white matter, and cerebrospinal fluid (CSF). The model accounts for random noise, magnetic field inhomogeneities, and biological variations of the tissues. Intensity measurements are mo...

提出了一种统计模型，用于表示单通道磁共振（MR）脑图像中主要组织类别的分布。利用该模型，将脑图像分割为灰质、白质和脑脊液（CSF）。该模型考虑了随机噪声、磁场不均匀性和组织的生物学变异。强度测量被...

We employ the new geometric active contour models, previously formulated, for edge detection and segmentation of magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound medical imagery. Our method is based on defining feature-based metrics on a given image which in turn leads to a novel snake paradigm in which the feature of interest may be considered to lie at the bottom of a p...

我们采用先前提出的新型几何主动轮廓模型，用于磁共振成像（MRI）、计算机断层扫描（CT）和超声医学图像的边缘检测与分割。我们的方法基于在给定图像上定义基于特征的度量，这进而导致一种新的蛇模型范式，其中感兴趣的特征可以被视为位于一个...的底部。

Positron emission tomography (PET) is a relatively lengthy brain imaging method. Because it is difficult for the subject to stay still during the data acquisition, head motion during scans is a source of image degradation. A simple data acquisition technique to reduce the effect of this problem is described. The technique associates the incoming data with the real-space position of the head. Durin...

正电子发射断层扫描（PET）是一种相对耗时的脑部成像方法。由于受试者在数据采集期间难以保持静止，扫描过程中的头部运动是图像质量下降的一个原因。本文描述了一种简单的数据采集技术来减少这一问题的影响。该技术将传入数据与头部的实际空间位置相关联。

Presents a new class of algorithms for penalized-likelihood reconstruction of attenuation maps from low-count transmission scans. We derive the algorithms by applying to the transmission log-likelihood a version of the convexity technique developed by De Pierro for emission tomography. The new class includes the single-coordinate ascent (SCA) algorithm and Lange's convex algorithm for transmission...

提出了一类新的算法，用于从低计数透射扫描数据中惩罚似然重建衰减图。我们通过对透射对数似然函数应用De Pierro为发射断层扫描开发的凸性技术的一个版本，推导出这些算法。新类别包括单坐标上升（SCA）算法和Lange的凸算法用于透射...

Using statistical methods the reconstruction of positron emission tomography (PET) images can be improved by high-resolution anatomical information obtained from magnetic resonance (MR) images. The authors implemented two approaches that utilize MR data for PET reconstruction. The anatomical MR information is modeled as a priori distribution of the PET image and combined with the distribution of t...

利用统计方法，正电子发射断层成像（PET）图像的重建可以通过从磁共振（MR）图像中获得的高分辨率解剖信息得到改善。作者实现了两种利用MR数据进行PET重建的方法。解剖MR信息被建模为PET图像的先验分布，并与...分布相结合。

The authors present a wavelet-based multigrid approach to solve the perturbation equation encountered in optical tomography. With this scheme, the unknown image, the data, as well as the weight matrix are all represented by wavelet expansions, thus yielding a multiresolution representation of the original perturbation equation in the wavelet domain. This transformed equation is then solved using a...

作者提出了一种基于小波的多网格方法来求解光学断层成像中的扰动方程。该方案中，未知图像、数据以及权重矩阵均用小波展开表示，从而在 wavelet 域中生成原始扰动方程的多分辨率表示。然后使用...

We present unpenalized and penalized weighted least-squares (WLS) reconstruction methods for positron emission tomography (PET), where the weights are based on the covariance of a model error and depend on the unknown parameters. The penalty function for the latter method is chosen so that certain a priori information is incorporated. The algorithms used to minimize the WLS objective functions gua...

我们提出了用于正电子发射断层扫描（PET）的无惩罚和带惩罚加权最小二乘（WLS）重建方法，其中权重基于模型误差的协方差，并依赖于未知参数。后一种方法的惩罚函数选择使得一定的先验信息被纳入。用于最小化WLS目标函数的算法...

The order in which the projections are applied in the algebraic reconstruction technique (ART) has a great effect on speed of convergence, accuracy, and the amount of noise-like artifacts in the reconstructed image. In this paper, a new projection ordering scheme for ART is presented: the weighted-distance scheme (WDS). It heuristically optimizes the angular distance of a newly selected projection...

在代数重建技术（ART）中，投影的应用顺序对收敛速度、精度以及重建图像中类似噪声的伪影数量有显著影响。本文提出了一种新的ART投影排序方案：加权距离方案（WDS）。它启发式地优化新选投影的角度距离...

A reliability evaluation technique was used to examine the reliability of an image analysis system of the trabecular pattern and to determine the contribution of three possible sources of error variance. Two series of radiographs were taken of 14 lumbar vertebral slices (28 radiographs). Every radiograph was placed on a viewing box for digitization four times by a single operator (112 positions of...

采用可靠性评估技术来检验骨小梁模式图像分析系统的可靠性，并确定三个可能的误差方差来源的贡献。对14个腰椎骨切片拍摄了两组X光片（共28张X光片）。每张X光片由一名操作员在观察箱上放置四次进行数字化处理（112个位置...）

The expectation-maximization maximum-likelihood (EM-ML) algorithm belongs to a family of algorithms that compute positron emission tomography (PET) reconstructions by iteratively solving a large linear system of equations. The authors describe a preprocessing scheme for automatically focusing the attention, and thus the computational resources, on a subset of the equations and unknowns. Experiment...

期望最大化最大似然（EM-ML）算法属于通过迭代求解大型线性方程组来计算正电子发射断层扫描（PET）重建的算法族。作者描述了一种预处理方案，用于自动将注意力（从而计算资源）集中在方程和未知数的子集上。实验...