Volume 19, Issue 5

Derives approximate analytical expressions for the local impulse response and covariance of images reconstructed from fully three-dimensional (3-D) positron emission tomography (PET) data using maximum a posteriori (MAP) estimation. These expressions explicitly account for the spatially variant detector response and sensitivity of a 3-D tomograph. The resulting spatially variant impulse response and covariance are computed using 3-D Fourier transforms. A truncated Gaussian distribution is used to account for the effect on the variance of the nonnegativity constraint used in MAP reconstruction. Using Monte Carlo simulations and phantom data from the microPET small animal scanner, the authors show that the approximations provide reasonably accurate estimates of contrast recovery and covariance of MAP reconstruction for priors with quadratic energy functions. They also describe how these analytical results can be used to achieve near-uniform contrast recovery throughout the reconstructed volume.

推导了使用最大后验（MAP）估计从全三维（3-D）正电子发射断层扫描（PET）数据重建图像的局部脉冲响应和协方差的近似解析表达式。这些表达式明确考虑了三维断层扫描仪的空间变化探测器响应和灵敏度。使用三维傅里叶变换计算得到的空间变化脉冲响应和协方差。采用截断高斯分布来解释MAP重建中非负性约束对方差的影响。通过蒙特卡罗模拟和来自microPET小动物扫描仪的体模数据，作者表明这些近似方法能够为具有二次能量函数的先验提供对比度恢复和协方差的合理准确估计。他们还描述了如何利用这些分析结果在整个重建体积中实现接近均匀的对比度恢复。

Computational burden is a major concern when an iterative algorithm is used to reconstruct a three-dimensional (3-D) image with attenuation, detector response, and scatter corrections. Most of the computation time is spent executing the projector and backprojector of an iterative algorithm. Usually, the projector and the backprojector are transposed operators of each other. The projector should mo...

当使用迭代算法重建具有衰减、探测器响应和散射校正的三维（3-D）图像时，计算负担是一个主要问题。大部分计算时间用于执行迭代算法的投影器和反投影器。通常，投影器和反投影器是互为转置的算子。投影器应该

Presents a preliminary study of list-mode likelihood reconstruction of images for a rectangular positron emission tomograph (PET) specifically designed to image the human breast. The prospective device consists of small arrays of scintillation crystals for which depth of interaction is estimated. Except in very rare instances, the number of annihilation events detected is expected to be far less t...

介绍了一项初步研究，针对专门设计用于成像人类乳腺的矩形正电子发射断层扫描（PET）的列表模式似然重建图像。该前瞻性设备由小阵列的闪烁晶体组成，可估计相互作用深度。除非在极少数情况下，检测到的湮灭事件数量预计将远少于...

Increasingly, three dimensional (3-D) imaging technologies are used in medical diagnosis, for therapy planning, and during interventional procedures. The authors describe the possibilities of fast 3-D-reconstruction of high-contrast objects with high spatial resolution from only a small series of two-dimensional (2-D) planar radiographs. The special problems arising from the intended use of an ope...

三维（3-D）成像技术越来越多地用于医疗诊断、治疗计划和介入手术过程中。作者描述了仅从少量二维（2-D）平面X线片即可快速重建高对比度物体并具有高空间分辨率的可能性。由于预期使用的操作...所带来的特殊问题

The authors have evaluated the performance of two three-dimensional (3-D) reconstruction algorithms with data acquired from microPET, a high resolution tomograph dedicated to small animal imaging. The first was a linear filtered-backprojection algorithm (FBP) with reprojection of the missing data, and the second was a statistical maximum a posteriori probability algorithm (MAP). The two algorithms...

作者评估了两种三维（3-D）重建算法在microPET（一种专门用于小动物成像的高分辨率断层成像仪）数据上的性能。第一种是线性滤波反投影算法（FBP），带有缺失数据的重投影；第二种是统计最大后验概率算法（MAP）。两种算法...

Artifacts can result when reconstructing a dynamic image sequence from inconsistent, as well as insufficient and truncated, cone beam single photon emission computed tomography (SPECT) projection data acquired by a slowly rotating gantry. The artifacts can lead to biases in kinetic model parameters estimated from time-activity curves generated by overlaying volumes of interest on the images. Howev...

当从由慢速旋转机架采集的不一致、不充分且截断的锥束单光子发射计算机断层扫描（SPECT）投影数据重建动态图像序列时，可能会产生伪影。这些伪影可能导致通过将感兴趣区域叠加在图像上生成的时间-活动曲线估计的动力学模型参数出现偏差。

This paper addresses the long object problem in helical cone-beam computed tomography. The authors present the PHI-method, a new algorithm for the exact reconstruction of a region-of-interest (ROI) of a long object from axially truncated data extending only slightly beyond the ROI. The PHI-method is an extension of the Radon-method, published by Kudo et al. in Phys. in Med. and Biol., vol. 43, p. ...

本文解决了螺旋锥束计算机断层扫描中的长物体问题。作者提出了PHI方法，这是一种新算法，用于从仅略超出感兴趣区域（ROI）的轴向截断数据中精确重建长物体的感兴趣区域。PHI方法是Radon方法的扩展，由Kudo等人在《Phys. in Med. and Biol.》第43卷中发表。

Methods of quantitative emission computed tomography require compensation for linear photon attenuation. A current trend in single-photon emission computed tomography (SPECT) and positron emission tomography (PET) is to employ transmission scanning to reconstruct the attenuation map. Such an approach, however, considerably complicates both the scanner design and the data acquisition protocol. A dr...

定量发射计算机断层扫描方法需要对线性光子衰减进行补偿。当前单光子发射计算机断层扫描（SPECT）和正电子发射断层扫描（PET）的一个趋势是使用透射扫描来重建衰减图。然而，这种方法大大复杂化了扫描仪设计和数据采集协议。一个...

Localization ROC (LROC) observer studies examined whether detector response compensation (DRC) in ordered-subset, expectation-maximization (OSEM) reconstructions helps in the detection and localization of hot tumors. Simulated gallium (Ga-67) images of the thoracic region were used in the study. The projection data modeled the acquisition of attenuated 93- and 185-keV photons with a medium-energy ...

局部化ROC（LROC）观察者研究考察了在有序子集期望最大化（OSEM）重建中进行探测器响应补偿（DRC）是否有助于检测和定位热肿瘤。研究中使用了模拟的胸部区域镓（Ga-67）图像。投影数据模拟了中能准直器下93 keV和185 keV衰减光子的采集。

A novel SPECT collimation method, termed the synthetic collimator, is proposed. The synthetic collimator employs a multiple-pinhole aperture and a high-resolution detector. The problem of multiplexing, normally associated with multiple pinholes, is reduced by obtaining projections at a number of pinhole-detector distances. Projections with little multiplexing are collected at small pinhole-detecto...

提出了一种新颖的SPECT准直方法，称为合成准直器。合成准直器采用多针孔孔径和高分辨率探测器。通过在不同针孔-探测器距离下获取投影，减少了通常与多针孔相关的复用问题。在小的针孔-探测器距离下收集复用程度低的投影，并利用这些投影重建高质量的二维和三维图像。

Monte Carlo simulations in nuclear medicine, with accurately modeled photon transport and high-quality random number generators, require precisely defined and often detailed phantoms as an important component in the simulation process. Contemporary simulation models predominantly employ voxel-driven algorithms, but analytical models offer important advantages. The authors discuss the implementatio...

核医学中的蒙特卡罗模拟，通过精确建模的光子传输和高质量的随机数生成器，需要精确定义且通常详细的模型作为模拟过程的重要组成部分。当代模拟模型主要采用体素驱动算法，但解析模型提供了重要的优势。作者讨论了实现...

True three dimensional (3-D) volume reconstruction from fully 3-D data in positron emission tomography (PET) has only a limited clinical use because of its large computational burden. Fourier rebinning (FORE) of the fully 3-D data into a set of 2-D sinogram data decomposes the 3-D reconstruction process into multiple 2-D reconstructions of decoupled 2-D image slices, thus substantially decreasing ...

真正的三维（3-D）体积重建在全三维正电子发射断层扫描（PET）数据中由于巨大的计算负担而仅具有有限的临床应用。将全三维数据通过傅里叶重排（FORE）分解为一组二维正弦图数据，将三维重建过程分解为多个解耦的二维图像切片的二维重建，从而大大减少计算量。

This paper presents a model-based vision system for dentistry that will assist in diagnosis, treatment planning, and surgical simulation. Dentistry requires an accurate three-dimensional (3-D) representation of the teeth and jaws for diagnostic and treatment purposes. The proposed integrated computer vision system constructs a 3-D model of the patient's dental occlusion using an intraoral video ca...

本文介绍了一种用于牙科的基于模型的视觉系统，可辅助诊断、治疗规划和手术模拟。牙科需要精确的牙齿和下颌骨三维（3-D）表示以进行诊断和治疗。所提出的集成计算机视觉系统使用口内视频摄像机构建患者牙齿咬合的三维模型...

Spatiotemporal reconstruction of cardiac-gated SPECT images permits one to obtain valuable information related to cardiac function. However, the task of reconstructing this four-dimensional (4-D) data set is computation intensive. Typically, these studies are reconstructed frame-by-frame: a nonoptimal approach because temporal correlations in the signal are not accounted for. In this work, the aut...

心脏门控SPECT图像的时空重建可以获取与心脏功能相关的宝贵信息。然而，重建这个四维数据集的任务计算量巨大。通常，这些研究逐帧重建：这是一种次优方法，因为未考虑信号中的时间相关性。在本工作中，自动...

Earlier investigations with BGO positron emission tomography (PET) scanners showed that the scatter correction technique based on multiple acquisitions with different energy windows are problematic to implement because of the poor energy resolution of BGO (22%), particularly for whole-body studies. The authors believe that these methods are likely to work better with NaI(Tl) because of the better ...

早期使用BGO正电子发射断层扫描（PET）扫描仪的研究表明，基于不同能量窗口多次采集的散射校正技术由于BGO的能量分辨率较差（22%），特别是在全身研究中实施起来存在问题。作者认为这些方法在使用NaI(Tl)时可能会更有效，因为其能量分辨率更好...

A multislice helical computed tomography (CT) half-scan (HS) reconstruction algorithm is proposed for cardiac applications. The imaging performances (in terms of the temporal resolution, z-axis resolution, image noise, and image artifacts) of the HS algorithm are compared to the existing algorithms using theoretical models and clinical data. A theoretical model of the temporal resolution performan...

提出了一种用于心脏应用的多层螺旋CT半扫描重建算法。通过理论模型和临床数据，将半扫描算法的成像性能（时间分辨率、Z轴分辨率、图像噪声和图像伪影）与现有算法进行了比较。时间分辨率性能的理论模型...

Addresses the issue of using deformable models to reconstruct an unknown attenuation map of the torso from a set of transmission scans. The authors assume the three-dimensional (3-D) distribution of attenuation coefficients to be piecewise uniform. They represent the unknown distribution by a set of closed surfaces defining regions having the same attenuating properties. The methods of reconstruct...

解决了使用可变形模型从一组透射扫描中重建未知躯干衰减图的问题。作者假设衰减系数的三维分布是分段均匀的。他们通过一组定义具有相同衰减特性的区域的封闭曲面来表示未知分布。重建方法...

The authors present a (spiral + circles) scan cone beam reconstruction algorithm in which image reconstruction proceeds via backprojection in the object space. In principle, the algorithm can reconstruct sectional region-of-interest (ROI) in a long object. The approach is a generalization of the cone beam backprojection technique developed by Kudo and Saito (1994) in two aspects: the resource-dema...

作者提出了一种（螺旋+圆形）扫描锥束重建算法，其中图像重建通过在对象空间中进行反投影来实现。原则上，该算法可以重建长物体中的截面感兴趣区域（ROI）。该方法在两个方面推广了Kudo和Saito（1994）开发的锥束反投影技术：资源需求...

The calculation of the intrinsic efficiency of individual crystals is one of the steps needed to obtain accurate images of the radioisotope distribution in positron emission tomography (PET). These efficiencies can be computed by comparing the number of coincidence counts obtained when the crystals are equally illuminated by the same source. However, because the number of coincidence counts acquir...

计算单个晶体的内在效率是获得正电子发射断层扫描（PET）中放射性同位素分布准确图像所需的步骤之一。这些效率可以通过比较当晶体被同一源均匀照射时获得的符合计数数量来计算。然而，由于符合计数的数量获取...

Positron emission tomography (PET) [/sup 15/O] activation studies have benefited significantly from three-dimensional (3-D) data acquisition. However, they have been slow to take advantage of new 3-D reconstruction techniques. Compared with the widely used 3-D reprojection reconstruction (3DRP), the advantage of signal and noise for iterative algorithms has been outweighed by concern about long an...

正电子发射断层扫描（PET）[15O]水激活研究已从三维（3-D）数据采集中显著受益。然而，它们在利用新的3-D重建技术方面进展缓慢。与广泛使用的3-D反投影重建（3DRP）相比，迭代算法在信噪比方面的优势因对长...的担忧而被抵消。