圆轨道锥束重建中Radon空间数据缺失

实际工程中广泛采用的圆轨道锥束CT重建算法(FDK类算法)中,只有在小锥角(<±5°)的条件下才能较好地重建。为了克服这一缺点,增大圆轨道可重建的锥角范围,推导了圆轨道锥束重建中R adon空间数据缺失与锥角的关系,并基于这一关系提出了基于不同半径的两个同心圆轨道的“改进型误差减小”(im proved error reduction-based,IERB)算法,利用估算的重建误差改善重建结果。数值仿真实验结果表明,IERB算法在锥角≤±10°时都能获得相当好的重建结果,在锥角更大时也可适用于一定的区域。该算法不适用于数据缺失过多的区域。     

基于转角增量关系的FDK锥束重建改进算法

单圆形轨迹不能满足锥束投影精确重建的充要条件是经典FDK算法出现锥向衰减伪像的根本原因.通过斜平面转角增量关系的分析,推导出同锥角斜平面间转角及其增量的计算关系,进而得出FDK算法是对同锥角斜平面族上有限视角的投影数据进行重建,并且在滤波反投影重建过程中存在转角关系不匹配问题.针对上述两个问题,提出了一种利用转角及其增量关系对FDK算法进行改进的新方法,改进思路也进一步推广到T-FDK算法中.Shepp-Logan模型的仿真实验结果表明在适中或较大锥角情况下,改进算法显著改善了FDK算法所存在的锥向衰减伪像.     

一种基于STL样本的锥束CT快速仿真方法

针对STL样本基元,根据锥束CT仿真投影的特点,研究了一套基于八叉树的锥束CT仿真投影快速计算方法,并采用SIMD技术对投影计算中的关键部分进行并行计算,进一步提高了生成仿真投影图象的速度。实验结果表明,在保证投影图象精度的前提下,该方法较之于UG样本投影计算有65～90倍左右的加速比,极大地提高了锥束CT仿真投影的计算速度,增强了仿真系统的实用性。     

医用直线加速器获取锥形束CT的图像空间扩展技术

提出了一种改进的锥形束CT(CBCT)图像获取流程,并在此基础上开发算法实现了CBCT图像的空间扩展.对实现算法进行了详细描述,并从放射剂量学角度对用于放射剂量计算可行性进行验证,相同放疗计划下对比胸部计划CT和扩展CBCT剂量计算结果表明,全肺受照射剂量大于等于20Gy的相对体积平均相差0.5%±0.22%,全肺平均受照射剂量平均相差(38.2±8.82)cGy,因此认为扩展后CBCT图像用于放射剂量计算与计划CT无显著差异.该技术拓宽了锥形束CT在影像引导放射治疗中的应用范围,提高了肿瘤放射治疗的精度,为开展自适应放疗、准确评价放疗计划提供了科学手段,有广泛的临床应用前景.由此带来的更多低剂量辐射对患者正常器官及皮肤造成的损伤有待进一步开展临床研究.     

基于R-line算法的锥形束重构区域

基于R-line算法,对各种锥形束的源轨道的重构区域作了数学描述,给出了重构区域的定义并分析了重构区域的存在性,解析了正交双圆轨道、螺旋轨道以及鞍形轨道等典型轨道对应的重构区域的剖面特征,并讨论了轨道离散化对重构精度的影响.实验结果表明,重构区域的几何参数对空间中的生成点集有控制作用,轨道离散化后的重构点分布具有聚集性,重构剖面上误差分布不均匀.     

利用投影数据重排进行锥形束体积重建的改进算法

针对锥顶轨迹为单圆的锥形束体积重建问题,提出了一种基于平板检测器的T-FDK算法．不同于传统的FDK算法,该算法首先将锥形束投影数据重排为倾斜平行投影数据,然后再经过加权滤波和反投影重建,最后重建出待测物体的三维结构．数据仿真实验结果表明,该算法在保持与传统FDK算法有相同的计算复杂度的同时,重建图像的质量有了明显的提高,可以确保在较大的锥角范围内获得满意的重建图像．因而该算法在医学成像和无损探伤等领域具有重要的实用价值．     

Dual Energy CT Imaging in Cone-Beam Micro-CT for Improved Attenuation Coefficient Measurement

In order to improve micro-CT’s capability of accurate quantification of linear attenuation coefficient μ, a dual energy method was developed to correct beam hardening artifacts caused by the polychromatic spectra of X-ray tubes. In this method, two sets of scans, taken at different energy levels, were combined to create a synthetic monochromatic image. A physical polychromatic model of μ in dual energy imaging was developed with an iterative method to solve the model for a few selected pixels. To find a high-speed and effective computing approach, the physics model was approximated by a polynomial function of the measured intensities. The method was tested on a PMMA-aluminum phantom and CaCl2 admixtures. The results show that streak and cupping artifacts are completely eliminated and that the measurement of the reconstructed attenuation coefficient μ is observed to be over 95% accurate.     

Filtered Backprojection Reconstruction with Depth-Dependent Filtering

A direct filtered-backprojection(FBP) reconstruction algorithm is presented for circular cone-beam computed tomography(CB-CT) that allows the filter operation to be applied efficiently with shift-variant band-pass characteristics on the kernel function.Our algorithm is derived from the ramp-filter based FBP method of Feldkamp et al.and obtained by decomposing the ramp filtering into a convolution involving the Hilbert kernel(global operation) and a subsequent differentiation operation(local operation).The d...     

Exact Efficient Handling of Interrupted Illumination in Helical Cone-Beam Computed Tomography with Arbitrary Pitch

We present a theoretically-exact and stable computed tomography(CT) reconstruction algorithm that is capable of handling interrupted illumination and therefore of using all measured data at arbitrary pitch.This algorithm is based on a differentiated backprojection(DBP) on M-lines.First,we discuss the problem of interrupted illumination and how it affects the DBP.Then we show that it is possible to take advantage of some properties of the DBP to compensate for the effects of interrupted illumination in a mat...     

锥束CT仿真投影快速计算

针对离散体素模型仿真投影数据计算,提出了一种快速并行计算方法。首先从射线的对称性分析了投影数据的并行计算,然后通过Siddon算法来进行射线与体素的求交;结合SIMD技术实现了离散体素模型投影数据的快速并行计算。实验结果表明,在保持投影数据精度的同时,较之Siddon方法能够取得约1.9倍的加速比。