反投影

For decreasing the calculation amount of angle functions for obtaining projection address, the trigonometric functions' values are calculated in advance and stored into a table which can be indexed if needed.

反投影时为了减少求取投影地址时三角函数的运算，将三角函数值事先求得并存到查找表中，需要时调用。

A back projection method of the filtered back projecion algorithm is proposed based on passive raydriven technique and preinterpolation technique.

提出了滤波反投影（filtered back projection， FBP）算法的基于被动式射线驱动和预插值的反投影策略。

A back projection method of the filtered back projecion algorithm is proposed based on passive ray-driven technique and pre-interpolation technique.

提出了滤波反投影(filtered back projection， FBP)算法的基于被动式射线驱动和预插值的反投影策略。

According to this,the reconstruction algorithms such as Linear Back Projection,Filter Back Projection and projection rearrangement method cannot be applied directly and must be improved.

根据这一情况，在医学CT中常用的一些图像重建算法如反投影法、滤波反投影法和投影重排方法都必须加以改进才能引用。

The system is an integrated whole including simulation and real-time data gathering imaging, whose finite element model can be analyzed automatically and size can be adjusted. The isoline and nephogram drawing algorithm in finite element after-management have been realized.

伪迹的产生主要来自于测量数据中所包含的噪声和误差，对于反投影算法还有反投影理论本身所固有的星状伪迹。

We analyzed the main factors that influence on the quality of reconstruction image. These factors are filter function, projection data, sampling space and noise level in filter backprojection, and the choice of relaxation parameter, the fashion of data access, the choice of basis function and the estimate of optimum iterative times in algebra iterative algorithm.

详细分析了影响滤波反投影算法图像重建质量的基本因素(滤波函数的选取，投影数，抽样间距，噪音的大小)和代数重建算法图像重建质量的几个因素(松弛引子的选择，数据访问方式，基函数的选择，最优迭代次数的估计)。

A positive and negative projection method of object to be tested based on universal pattern display card includes using 3D texture to present rebuilt body data of object to be tested, calculating out directional vector array of ray outgoing point to detectors, storing said vector array into pattern display card to form directional vector texture, rotating directional vector texture and directional vector around rotary shaft to realize once of positive projection course on any projective angle, using 3D texture index technique to let virtual slab set position be not limited any more in negative projection course.

本发明属于投影探测与成像技术领域，其特点在于该方法含有以下步骤：把被测物体的重建体数据用三维纹理存储表示；预先计算射线出射点至平面探测器上个探测器之间的方向向量数组，并存储到通用图形显示卡中形成方向向量纹理；利用方向向量纹理与方向向量绕旋转轴旋转来实现任一投影角度的正投影过程的一次完成，无中间结果转存；在反投影过程中，利用三维纹理索引技术使虚拟切片组的放置位置不再受到限制。

The image reconstruction algorithms is thoroughly researched. The Filter Back Projection , Algebra Reconstruction Technology and fan beam data rearrangement algorithm used in medical computer tomography are improved. The NOSER algorithm, linear neural networks method and Hopfield neural networks method are presented and gain the better result of image reconstruction.

深入研究了图像重建算法，改进了医学CT的滤波反投影算法、代数重建技术和扇束投影数据重排方法，提出了带图像光滑约束的NOSER算法、线性神经网络方法和Hopfield神经网络方法，并得到了较好的图像重建结果。

On the basement of conventional direct fan-beam reconstruction, this paper gives a newly improved algorithm-"fast filtering-backprojection". This method utilizes the symmetrical circle geometry to sample projection data, and reconstructs image on the Polarcoordinate firstly, then translates this reconstructed image onto the cartesian coordinate system with two interpolating operations so that the computer can show the result image on the VGA screen. This algorithm rebates the calculating backprojection greatly, and shortens a few times of reconstructing time than same kinds of means. With the size of image enlarging, the reconstructing time abates with 2 exponent times. In addition, according to the idea of parallel-beam, we rearrange the fan-beams and reconstruct image using parallel-beam method fastly. The rearranging constraint condition is given here.

本文首先在传统的扇束直接重建方法的基础上，提出了一个改进的快速滤波反投影重建算法，它利用旋转采集投影数据的圆周对称的几何关系，先在极坐标系统内进行图象的重建，然后通过两次内插运算再将图象转换到计算机显示方式下的笛卡尔坐标系中去，该方法将以往的直接重建方法中的反投影时所需的运算大大降低，并将重建时间比同类方法缩短了几倍，而且随着重建图象的尺寸的增大，重建时间以2的指数次方倍相对缩短，并获得了较好质量的重建图象；另外，又根据平行束投影重建图象的思想，对扇形射束进行了重排，然后利用平行束重建图象的方法进行扇束的重建，并推导了&扇束重排重建图象&方法的约束条件。

Microstructure-evolution of the silicon nitride ceramics sample during sintering process was investigated by a synchrotron radiation X-ray computed tomography technique. The projection images of the sample were obtained during the sintering process in real-time. 2-D and 3-D reconstructed images were obtained by treating the projection images of different sintering periods with filter back projection arithmetic and digital image processing methods.

利用同步辐射CT技术，在氮化硅陶瓷样品烧结过程中对其进行实时投影成像，并应用滤波反投影算法和数字图像处理技术，得到了样品在整个烧结过程中内部微结构演化的二维和三维重建图像，实现了对陶瓷固相烧结过程实时、无损的观测。

This one mode pays close attention to network credence foundation of the businessman very much.

这一模式非常关注商人的网络信用基础。

Cell morphology of bacterial ghost of Pasteurella multocida was observed by scanning electron microscopy and inactivation ratio was estimated by CFU analysi.

扫描电镜观察多杀性巴氏杆菌细菌幽灵和菌落形成单位评价遗传灭活率。