Automatic calibration method of voxel size for cone-beam 3D-CT scanning system

For a cone-beam three-dimensional computed tomography （3D-CT） scanning system, voxel size is an important indicator to guarantee the accuracy of data analysis and feature measurement based on 3D-CT images. Meanwhile, the voxel size changes with the movement of the rotary stage along X-ray direction. In order to realize the automatic calibration of the voxel size, a new and easily-implemented method is proposed. According to this method, several projections of a spherical phantom are captured at different imaging positions and the corresponding voxel size values are calculated by non-linear least-square fitting. Through these interpolation values, a linear equation is obtained that reflects the relationship between the voxel size and the rotary stage translation distance from its nominal zero position. Finally, the linear equation is imported into the calibration module of the 3D-CT scanning system. When the rotary stage is moving along X-ray direction, the accurate value of the voxel size is dynamically exported. The experimental results prove that this method meets the requirements of the actual CT scanning system, and has virtues of easy implementation and high accuracy.     

Automatic calibration method of voxel size for cone-beam 3D-CT scanning system

For a cone-beam three-dimensional computed tomography (3D-CT) scanning system, voxel size is an important indicator to guarantee the accuracy of data analysis and feature measurement based on 3D-CT images. Meanwhile, the voxel size changes with the movement of the rotary stage along X-ray direction. In order to realize the automatic calibration of the voxel size, a new and easily-implemented method is proposed. According to this method, several projections of a spherical phantom are captured at different imaging positions and the corresponding voxel size values are calculated by non-linear least-square fitting. Through these interpolation values, a linear equation is obtained that reflects the relationship between the voxel size and the rotary stage translation distance from its nominal zero position. Finally, the linear equation is imported into the calibration module of the 3D-CT scanning system. When the rotary stage is moving along X-ray direction, the accurate value of the voxel size is dynamically exported. The experimental results prove that this method meets the requirements of the actual CT scanning system, and has virtues of easy implementation and high accuracy.     

螺旋锥束计算机断层成像倾斜扇束反投影滤波局部重建算法

螺旋锥束计算机断层成像(CT)作为常用的临床诊断工具,如何尽可能地减少其辐射剂量是热点研究领域之一.局部成像利用准直器减小射线直照区域,能够有效降低CT辐射剂量.然而,局部成像会造成投影数据横向截断,产生局部重建问题.现有螺旋反投影滤波(BPF)算法只能实现局部曲面重建,难以实现局部体区域重建.在圆轨迹扇束BPF算法的基础上,通过加权修正和坐标扩展,提出了螺旋锥束CT倾斜扇束反投影滤波(TFB-BPF)重建算法.该算法把重建区域按层划分,对各层构建倾斜的扇形束几何,并使用经过加权修正的TFB-BPF算法逐层进行重建.该算法最大的优势是滤波线(与原始螺旋锥束BPF算法中PI线等价)在二维平面内选择,算法更加简洁高效,并且能够应用于局部体区域的重建.实验结果表明,算法能够有效重建物体局部体区域,并且重建图像质量较好,没有明显的截断伪影.     

自适应光学系统变形镜控制电压预测

在校正大气湍流畸变波前相差的自适应光学系统中,利用基于Levenberg-Marquardt学习算法的非线性反向传播神经网络技术（LMBP）对变形镜控制电压进行预测。以对受横向风影响的大气湍流畸变波前斜率数据为研究对象,通过数值仿真方法,研究了基于LMBP算法的自适应光学系统变形镜电压非线性预测控制算法。通过实验发现,预测电压和变形镜实际控制电压拟合效果良好。讨论了回溯帧数对预测效果的影响,并与基于递推最小二乘（RLS）算法的线性预测算法进行比较。对比结果表明,基于LMBP算法的非线性电压预测方法比基于递推最小二乘法的线性电压预测方法能更有效地降低系统由伺服延迟引起的误差。     

半覆盖锥束CT中扁平物体的高效反投影滤波重建

全覆盖圆轨迹扫描的成像视野受探测器宽度限制, 对于大物体的成像效率较低.半覆盖扫描可以将成像视野扩展近1倍, 图像重建首推使用反投影滤波型算法. 反投影滤波型算法按PI线重建, 各PI线积分区间的不一致性导致通信和计算消耗大, 影响重建效率. 针对半覆盖成像中扁平形状物体的重建问题, 提出了一种改进的反投影滤波型算法, 且证明了当扁平物体的厚度小于2Rsin(2π/N_p) (R为扫描半径, N_p 为圆扫描一周均匀采集的投影数量)时, PI线积分区间的不一致性在数值计算过程中的误差是可以忽略的. 改进后的算法相比原半覆盖反投影滤波算法具有两个明显的优势: 一是数值计算过程中角度循环移至PI线循环之外, 算法的通信需求显著降低; 二是投影数据求导、反投影和沿PI线滤波三个步骤均能够并行计算, 算法的并行性得到增强.数值仿真与实际数据的实验结果表明, 本文算法与原半覆盖反投影滤波算法的重建精度相当, 但计算效率提高了4.6倍. 关键词： 锥束CT 半覆盖成像 反投影滤波 PI线     

Fast parallel algorithm for three-dimensional distance-driven model in iterative computed tomography reconstruction

The projection matrix model is used to describe the physical relationship between reconstructed object and projection.Such a model has a strong influence on projection and backprojection,two vital operations in iterative computed tomographic reconstruction.The distance-driven model(DDM) is a state-of-the-art technology that simulates forward and back projections.This model has a low computational complexity and a relatively high spatial resolution;however,it includes only a few methods in a parallel operation with a matched model scheme.This study introduces a fast and parallelizable algorithm to improve the traditional DDM for computing the parallel projection and backprojection operations.Our proposed model has been implemented on a GPU(graphic processing unit) platform and has achieved satisfactory computational efficiency with no approximation.The runtime for the projection and backprojection operations with our model is approximately 4.5 s and 10.5 s per loop,respectively,with an image size of 256×256×256 and 360 projections with a size of 512×512.We compare several general algorithms that have been proposed for maximizing GPU efficiency by using the unmatched projection/backprojection models in a parallel computation.The imaging resolution is not sacrificed and remains accurate during computed tomographic reconstruction.     

净信号预处理结合径向基偏最小二乘回归在血糖无创检测中的应用

为了提高人体血糖近红外光谱定量分析模型的预测精度,结合净信号预处理(NAP)算法和径向基偏最小二乘(RBFPLS)回归建立了一种适合于人体血糖测量的非线性建模方法NAP-RBFPLS。本文首先利用NAP对近红外光谱进行预处理来有效地提取原始光谱中仅与葡萄糖信号相关的光谱信息,从而有效地减弱了人体血液中水、白蛋白、血红蛋白、脂肪等成分的吸收干扰以及人体体温的变化、测量仪器本身的漂移、测量环境的变化和测量条件的变化引起的干扰因素与血糖变化的偶然相关问题;然后把净信号预处理后的近红外光谱数据通过RBFPLS建立了非线性定量分析模型来解决由于人体强散射引起的血糖浓度与近红外光谱之间的非线性关系,并与偏最小二乘(PLS)、基于净信号预处理的偏最小二乘(NAP-PLS)和RBFPLS这三种建模方法建立的定量分析模型进行了对比分析。实验结果表明,这两种方法相结合建立的非线性校正模型对预测集的预测精度有了很大的提高,这将对人体血糖浓度无创检测技术的研究具有实际应用价值。     

近红外透射光谱法检测三组分食用调和油含量的研究

以大豆油、花生油和玉米油三组分食用调和油为研究对象,采集样品在10 000～4 200 cm-1范围内的近红外透射光谱,对光谱进行不同预处理后结合偏最小二乘法分别建立调和油中三组分的定量分析模型,并检验模型预测的准确度和精密度。结果显示,一阶导数结合多元散射校正(FD+MSC),一阶导数结合减去一条直线(FD+SLS)以及一阶导数(FD)进行光谱预处理,可以得到大豆油、花生油以及玉米油含量的最优定标模型,分别是在5 450.1～4 597.7 cm-1,7 521.3～6 098.1 cm-1和9 993.7～7 498.2 cm-1谱区范围内获得的。各预测模型的相关系数R2和预测均方根RMSEP分别为99.89%,1.09%;99.88%,1.17%;99.76%,1.48%;配对t检验值在0.371 9～0.007 9之间;预测相对标准偏差RSD均小于1.50%。表明傅里叶变换近红外透射光谱分析技术可以快速准确可靠地检测三组分食用调和油中大豆油、花生油、玉米油的含量。