Volume 20, Issue 11

The authors address the problem of applying spatial transformations (or "image warps") to diffusion tensor magnetic resonance images. The orientational information that these images contain must be handled appropriately when they are transformed spatially during image registration. The authors present solutions for global transformations of three-dimensional images up to 12-parameter affine complexity and indicate how their methods can be extended for higher order transformations. Several approaches are presented and tested using synthetic data. One method, the preservation of principal direction algorithm, which takes into account shearing, stretching and rigid rotation, is shown to be the most effective. Additional registration experiments are performed on human brain data obtained from a single subject, whose head was imaged in three different orientations within the scanner. All of the authors' methods improve the consistency between registered and target images over naive warping algorithms.

作者解决了将空间变换（或“图像扭曲”）应用于扩散张量磁共振图像的问题。这些图像包含的方向信息在图像配准过程中进行空间变换时必须得到适当处理。作者提出了三维图像全局变换的解决方案，达到12参数仿射复杂度，并说明了如何将其方法扩展到更高阶变换。提出了几种方法，并使用合成数据进行了测试。其中一种方法，即主方向保留算法，考虑了剪切、拉伸和刚体旋转，被证明是最有效的。还对从单个受试者获得的人脑数据进行了额外的配准实验，该受试者的头部在扫描仪内以三种不同方向成像。作者的所有方法都比简单的扭曲算法提高了配准图像和目标图像之间的一致性。

Reports on the design and test of an image processing algorithm for the localization of the optic disk (OD) in low-resolution (about 20 /spl mu//pixel) color fundus images. The design relies on the combination of two procedures: 1) a Hausdorff-based template matching technique on edge map, guided by 2) a pyramidal decomposition for large scale object tracking. The two approaches are tested against...

报告了一种图像处理算法的设计和测试，用于在低分辨率（约20微米/像素）彩色眼底图像中定位视盘。该设计依赖于两种方法的结合：1）基于Hausdorff的模板匹配技术，在边缘图上进行，由2）用于大尺度目标跟踪的金字塔分解引导。这两种方法针对...

The human cerebral cortex is topologically equivalent to a sheet and can be considered topologically spherical if it is closed at the brainstem. Low-level segmentation of magnetic resonance (MR) imagery typically produces cerebral volumes whose tessellations are not topologically spherical. The authors present a novel algorithm that analyzes and constrains the topology of a volumetric object. Grap...

人类大脑皮层在拓扑上等同于一个薄片，如果在脑干处闭合，则可视为拓扑球体。磁共振（MR）图像的低层分割通常会产生其曲面细分非拓扑球形的脑体积。作者提出了一种新颖的算法，用于分析和约束体积对象的拓扑结构。

Image acquisition techniques often suffer from low signal-to-noise ratio (SNR) and/or contrast-to-noise ratio (CNR). Although many acquisition techniques are available to minimize these, post acquisition filtering is a major off-line image processing technique commonly used to improve the SNR and CNR. A major drawback of filtering is that it often diffuses/blurs important structures along with noi...

图像采集技术通常存在低信噪比和/或低对比度噪声比。尽管有许多采集技术可用于最小化这些问题，但采集后滤波是一种常用的离线图像处理技术，用于改善信噪比和对比度噪声比。滤波的一个主要缺点是它常常与噪声一起扩散/模糊重要结构。

The authors conducted positron emission tomography (PET) image reconstruction experiments using the wavelet transform. The Wavelet-Vaguelette decomposition was used as a framework from which expressions for the necessary wavelet coefficients might be derived, and then the wavelet shrinkage was applied to the wavelet coefficients for the reconstruction (WVS). The performances of WVS were evaluated ...

作者使用小波变换进行了正电子发射断层扫描（PET）图像重建实验。采用Wavelet-Vaguelette分解作为框架，从中推导出必要的小波系数的表达式，然后将小波收缩应用于小波系数以进行重建（WVS）。评估了WVS的性能……

Motion artifacts have been identified as a problem in medical tomography systems. While computed tomography (CT) imaging has been getting faster, there remains a need to detect and compensate for motions in clinical follow-up of neurological patients (multiple sclerosis, tumors, stroke, etc.), in cardiac imaging, and in any area in which failing to detect a motion artifact may lead to misdiagnosis...

运动伪影已被确定为医学断层扫描系统中的一个问题。尽管计算机断层扫描（CT）成像速度越来越快，但在神经疾病患者（多发性硬化、肿瘤、中风等）的临床随访、心脏成像以及任何未能检测到运动伪影可能导致误诊的领域中，仍然需要检测和补偿运动。

In magnetic resonance (MR) imaging, limited data sampling in /spl kappa/-space leads to the well-known Fourier truncation artifact, which includes ringing and blurring. This problem is particularly severe for MR spectroscopic imaging, where only 16-24 points are typically acquired along each spatial dimension. Several methods have been proposed to overcome this problem by incorporating prior infor...

在磁共振（MR）成像中，k-space的有限数据采样导致了众所周知的傅里叶截断伪影，包括振铃和模糊。这个问题在MR波谱成像中尤为严重，因为每个空间维度通常只采集16-24个点。已有几种方法通过引入先验信息来克服这一问题...

Although there have been recent advances in echocardiography, many studies remain suboptimal due to poor image quality and unclear blood-myocardium border. The authors developed a novel image processing technique, cardiac variability imaging (CVI), based on the variance of pixel intensity values during passage of ultrasound microbubble contrast into the left ventricle chamber, with the aim of enha...

尽管近年来超声心动图取得了进展，但由于图像质量差和血液-心肌边界不清晰，许多研究仍不理想。作者开发了一种新的图像处理技术，即心脏变异性成像（CVI），基于超声微泡对比剂进入左心室腔过程中像素强度值的方差，旨在增强...

In quasi-static magnetic resonance elastography, strain images of a tissue or material undergoing deformation are produced. In this paper, the signal/noise (S/N) ratio [SNR] of elastographic strain images, as measured by a phase-contrast technique, is analyzed. Experiments are conducted to illustrate how diffusion-mediated signal attenuation limits maximum strain SNR in small displacement cases, w...

在准静态磁共振弹性成像中，产生正在变形的组织或材料的应变图像。本文分析了通过相位对比技术测量的弹性应变图像的信噪比（SNR）。实验表明扩散介导的信号衰减如何在小位移情况下限制最大应变信噪比，

Describes a method that uses the linear phase acquired during the readout period due to chemical shift to generate individual magnetic resonance (MR) images of chemically shifted species. The method utilizes sets of Fourier (or /spl kappa/-space) data acquired with different directions of the readout gradient and a postprocessing algorithm to generate chemical shift images. The methodology is deve...

描述了一种方法，该方法利用读出期间由于化学位移而获得的线性相位，生成化学位移物种的单独磁共振（MR）图像。该方法利用不同读出梯度方向采集的傅里叶（或κ空间）数据集以及后处理算法来生成化学位移图像。该方法的开发...