基于几何代数 SURF 的三维医学图像配准研究

三维医学图像可辅助医生的临床诊疗,不同模态三维图像通过配准后,可为医生提供更全面的病患信息,而传统三维多 模态医学图像配准的精度不高、耗时较长且易受干扰。 首先搭建 Hessian 四维尺度空间,将加速稳健特征(SURF)框架拓展至三 维,然后基于几何代数构造了梯度角度不变性的三维特征点描述子,以丰富特征点信息;再设计快速空间寻优算法,不仅可保证 配准精度,且提高配准稳定性;最后,采用数据一致性较好的 RIRE 公开数据集和合作附属医院提供的个性化临床实例数据开 展实验。 实验评估中,以手动配准作为金标准,公开库和临床实例图像的配准均值误差都不超过 3 mm,配准相似性超过 99. 1% ;抗扰实验中混入高斯噪声,均值误差仍不超过 3. 5 mm,相似性超过 98. 9% 。 实验结果表明,基于几何代数 SURF 的三维 配准方法的精度更高且稳定性更强,可为临床适用提供理论基础与诊疗预案。     

基于Fourier-Meliin算法的干涉图像配准

提出了采用Fourier-Mellin算法对大孔径静态干涉成像光谱仪的原始干涉图像进行配准的方法,用于校正由于推扫平台系统姿态不稳所造成的失真.采用Fourier-Mellin算法和相位相关算法求取干涉图像的旋转角度和缩放及平移参数,并通过多帧未校正的图像和校正后的图像分别拼接成大面积地域图像来验证算法.实验结果表明,通过人眼判断,可以实现对图像的配准,配准精度达到1Pixel,基本满足将LASIS原始干涉图校正为不失真图像的要求.     

动态电容层析成像图像重建算法

提出了融合ECT测量信息和被测对象动态演化信息的新型图像重建模型;基于Tikhonov正则化方法,建立一个同时考虑了ECT测量信息、被测对象动态演化信息、时间与空间约束的新型图像重建目标泛涵,将图像重建问题转化为最优化问题;提出了集成分裂Bregman迭代法优势的新型算法求解该目标泛涵。数值仿真结果表明,所提出的图像重建算法其图像重建质量均优于OIOR算法、STR算法及PLI算法;同时由于所提出的图像重建算法同时考虑了测量数据和重建模型的不精确性,其抵抗测量噪声的能力得以提高。     

Non‐rigid alignment in electron tomography in materials science

Electron tomography is a key technique that enables the visualization of an object in three dimensions with a resolution of about a nanometre. High‐quality 3D reconstruction is possible thanks to the latest compressed sensing algorithms and/or better alignment and preprocessing of the 2D projections. Rigid alignment of 2D projections is routine in electron tomography. However, it cannot correct misalignments induced by (i) deformations of the sample due to radiation damage or (ii) drifting of the sample during the acquisition of an image in scanning transmission electron microscope mode. In both cases, those misalignments can give rise to artefacts in the reconstruction. We propose a simple‐to‐implement non‐rigid alignment technique to correct those artefacts. This technique is particularly suited for needle‐shaped samples in materials science. It is initiated by a rigid alignment of the projections and it is then followed by several rigid alignments of different parts of the projections. Piecewise linear deformations are applied to each projection to force them to simultaneously satisfy the rigid alignments of the different parts. The efficiency of this technique is demonstrated on three samples, an intermetallic sample with deformation misalignments due to a high electron dose typical to spectroscopic electron tomography, a porous silicon sample with an extremely thin end particularly sensitive to electron beam and another porous silicon sample that was drifting during image acquisitions.     

一种不同分辨率异类图的融合算法

将较高分辨率的图像分解到各个较低分辨率，对最低分辨率的图像采用先加权平均，进而取亮度极大值的融合方法进行融合，并对上述最低分辨率上的融合图像和较高分辨率的图像利用基于Kalman滤波的多分辨图像融合算法进行融合；上述2步重复进行，最后可得最高分辨率下综合所有图像信息的融合图像。实验表明，本文所介绍的图像融合算法是有效的。     

基于MAP的自适应图像配准及超分辨率重建

图像超分辨率重建是一种将多幅低分辨率图像合成为高分辨率图像的技术.当前的超分辨重建技术主要分为图像配准和超分辨率重建2个步骤,提出一种基于最大后验概率的图像超分辨率重建算法,将这2个步骤合二为一;与此同时,为了解决配准参数以及点扩展函数估计值的不精确性问题,在每一幅低分辨率图像代价函数的残差项引入了自适应加权系数并随之...     

基于超分辨率重建的亚像素图像配准

针对低分辨率图像在配准过程中精度较低的问题,提出了一种基于超分辨率重建的亚像素图像配准方法。首先,对具有1至9像素位移的图像序列进行10倍降采样,获取具有0.1至0.9亚像素位移的图像序列。然后,根据图像的获取过程建立数学模型,以Bayes理论为基础,使用最大后验概率法(MAP)对亚像素位移低分辨率图像进行超分辨率重建,获取高分辨率图像。最后,使用具有亚像素配准精度的扩展相位相关法对图像进行配准。配准实验与噪声实验表明,所提方法的最大配准误差为0.03pixel,能实现对低分辨率图像的亚像素级配准,具有配准精度高、噪声抗干扰能力强等特点,可同时满足可见光图像与红外图像的高精度配准要求。     

基于3D SPIHT的高光谱图像压缩技术

将三维多级树集合分裂(3D SPIHT)算法用于高光谱图像的压缩。根据高光谱图像的特点进行波段分组以得到处理单元,对各组分别进行三维小波变换,去除谱间和谱内冗余;利用3D SPIHT算法对变换后小波系数进行编码,去除系数之间的冗余。采用整数小波和浮点小波分别进行无损和有损压缩仿真,AVIRIS和OMIS实验结果表明,在bit/pixel为1的条件下,平均PSNR比准三维方法分别高0.91 dB和1.38 dB,且算法具有嵌入式、可伸缩性等优点,但无损压缩的平均bit/pixel比基于预测的方法高0.308和0.159。3D SPIHT算法用于高光谱图像压缩可以获得较好的有损性能,但无损压缩性能逊于基于预测的方法。     

应用于紫外检测技术的ICA图像融合算法

针对高压电气设备电晕放电故障点定位问题,对ICA图像融合算法、紫外检测技术和紫外成像系统等方面进行了研究。将ICA图像融合算法运用到高压设备电晕放电检测中,根据高压设备局部放电会发出紫外光的原理和紫外光波长在日盲200 nm~400 nm波段的特点,对高压设备局部放电区域采集紫外光图像和可见光图像进行图像融合,在融合图像中准确定位局放故障点。研究针对紫外图像和可见光图像灰度直方图差别大的特点,对传统Fast ICA算法进行优化,以优化后的权值对融合系数进行加权处理,建立融合规则使局放故障点表达更加清晰,并将算法运用于紫外成像系统。研究结果表明,改进后的Fast ICA算法对比于紫外成像仪的其他算法所得图像信息更加丰富、定位更加精准,融合图像可以有效地定位高压设备电晕放电故障点。     

面向挤出中聚合物形态的层析图像处理方法的研究

依据光学信息论中的多维随机变量的联合熵、条件熵、平均互信息之间关系和互信息的链式法则,提出了面向挤出中聚合物形态的层析图像处理方法.它包括层析图像中的背景与分离、目标标度变换、亚像素插补的图像预处理和多模式目标特征图像的提取和测量.实验表明,通过该方法不仅能将目标形态从目标与背景之比为1∶9的层析图像中分辨出来,而且能提高目标图像的空间分辨率30%,解决了由于目标图像信息量小、对比度差而使得层析图像测量方法难以在工程中应用的问题.     

3D imaging of nanomaterials by discrete tomography

The field of discrete tomography focuses on the reconstruction of samples that consist of only a few different materials. Ideally, a three-dimensional (3D) reconstruction of such a sample should contain only one grey level for each of the compositions in the sample. By exploiting this property in the reconstruction algorithm, either the quality of the reconstruction can be improved significantly, or the number of required projection images can be reduced. The discrete reconstruction typically contains fewer artifacts and does not have to be segmented, as it already contains one grey level for each composition.     

椭圆匹配法在空心涡轮叶片3D配准中的应用

在三维CT设备对空心涡轮叶片进行无损检测时会存在定位偏差问题 ,三维数字样品图像模型的配准是关键的一步。本文首先对CT切片图像提取轮廓点 ,然后借助转动惯量计算惯量椭圆并进一步对惯量椭圆匹配以获得所需的几何变换的参数 ,从而实现CT图像与理论模型之间的配准。仿真结果表明 :此方法用于空心涡轮叶片 3 D配准可取得满意效果     

梯度引导电学成像自适应网格生成方法

电学层析成像是一种观测场域内电导率分布的无损检测技术。有限元法是求解电学层析成像问题的常用方法。其作为线性化的近似方法,剖分单元的大小会影响有限元法求解的精度。更密的尺寸可以提高重建图像的空间分辨率,但会增加计算成本,同时未知量个数的增加会加剧逆问题的欠定性。针对上述问题,提出一种基于图像梯度的自适应网格生成方法。根据初始重建图像的梯度,自适应地提高内含物区域的网格密度,降低其他区域的网格密度,并对场域边界进行精确拟合来优化被测场域的网格剖分。通过仿真与实验研究对比分析了所提方法与常用网格剖分方法。结果表明,所提方法的重建结果图像误差平均降低15%,相关系数平均提高7%,因此所提方法在不显著增加或减少网格数的情况下,可以有效提高内含物的重建精度和图像重建质量。     

Towards automated electron holographic tomography for 3D mapping of electrostatic potentials

Electron-holographic tomography (EHT), that is, the combination of off-axis electron holography with electron tomography, was successfully applied for the quantitative 3D mapping of electrostatic potentials at the nanoscale. Here we present the first software package (THOMAS) for semi-automated acquisition of holographic tilt series, a prerequisite for efficient data collection. Using THOMAS, the acquisition time for a holographic tilt series, consisting of object and reference holograms, is reduced by a factor of five on average, compared to the previous, completely manual approaches. Moreover, the existing software packages for retrieving amplitude and phase information from electron holograms have been extended, now including a one-step procedure for holographic tilt series reconstruction. Furthermore, a modified SIRT algorithm (WSIRT) was implemented for the quantitative 3D reconstruction of the electrostatic potential from the aligned phase tilt series. Finally, the application of EHT to a polystyrene latex sphere test-specimen and a pn-doped Ge ‘needle’-shaped specimen are presented, illustrating the quantitative character of EHT. For both specimens the mean inner potential (MIP) values were accurately determined from the reconstructed 3D potential. For the Ge specimen, additionally the ‘built-in’ voltage across the pn junction of 0.5 V was obtained.     

Nonlinear image reconstruction using a GA-ECT technique in electrical capacitance tomography

Electrical capacitance tomography (ECT) is a non-invasive measurement technique that estimates the dielectric permittivity distribution of an inhomogeneous object from the boundary potentials at floating electrodes or mutual capacitances. In this paper, a stochastic inverse technique based on genetic algorithm (GA-ECT) is developed, which is adapted to the two different methods, i.e. potential measurement and capacitance measurement. Numerical simulation results are presented to evaluate the inverse technique both for noise free and noisy data and the results show that quantitative image can be reconstructed not only with the low permittivity contrast but also with the high contrast. Furthermore, the influence of a priori knowledge to image reconstruction is discussed.     

高精度影像测量系统中图像的超分辨率重建

为了提高影像测量系统的测量精度,研究了基于微位移错位的多幅图像超分辨重建技术.考虑制作成本和制作难度,提出了一种不苛求精确微位移的超分辨率重建技术.首先,获取随机微位移图像序列;然后,利用被测对象中易于实现高精度提取的特征点或采用模板衬底中的特征点计算出图像序列间的准确位移关系;最后,根据本文提出的数学模型重建出高分辨...     

基于Demons算法的变形掌纹归一化方法研究

非接触采集是主流掌纹采集方式,但其低约束性可能会导致手掌摆放方式不定,与传感器距离不定,从而引起手掌变形,尤其是手掌平面和传感器平面不平行导致的局部变形问题,这将影响后续特征提取,降低识别率。针对此问题,考虑到人手本身是非刚体的特点,提出基于Demons非刚性配准算法的变形掌纹归一化校正模型,进一步增强变形图像与标准图像的相似性,弥补了传统刚性方法校正效果不佳的缺陷。首先使用改进的Demons非刚性配准算法进行变形掌纹的归一化校正,再使用测度指标进行效果评价,结果表明:在任取的图像序列内,与传统的基于归一化互信息(NMI)的刚性配准方法相比,NMI最高提升3.64%,相关系数(COEF)最高提升156.25%,均方误差(MSE)最高降低81.63%,各指标均优于基于NMI的刚性配准方法,验证了本文方法的有效性和优越性,为后续的特征提取和识别创造了有利条件。     

基于预优化变换的电容层析成像图像重建算法

本文提出了一种新型快速电容层析成像的图像重建算法。该方法首先将图像重建的病态问题转化为泛函极小化问题，然后采用Fletcher-Reeves算法（FR）有效地求解该泛函，并在求解的过程中引入物理意义上的约束使获得的解更符合实际情况。数值实验表明该算法的图像重建效果优于线性反投影法、Tikhonov正则法和Landweber迭代法，而且该算法具有较强的抗噪声能力。     

基于分支限界的三维曲面全局配准方法

在三维测量中常需要将测量点云数据与已知曲面模型进行配准。采用隐式函数建立点云数据到曲面模型的距离场,进而进行非线性优化求解可以有效提升配准效率。然而由于点到曲面的近似距离及刚性变换的约束,其误差函数呈现非凸性而导致迭代极易陷入局部最优。为实现全局配准,提出了一种利用分支限界算法搜索点到曲面近似距离平方和误差函数最小化变换参数的方法。通过确定刚体变换参数空间中误差函数的上下界限加快搜索,并结合一种等效距离公式的LevenbergMarquardt算法优化的局部配准方法加速收敛并保证配准精度。三维模型的配准实验与分析验证了本文全局配准方法的有效性。     

Study of multi-electrode excitation mode for 3D electrical resistance tomography

Multi-electrode excitation is an effective way to improve the performance of 3D electrical tomography (ET) system compared with single electrode excitation. This paper systematically discusses various sensing strategies for multi-electrode excitation with different combinations in radial and axial directions. A typical 3 × 8 3D ERT sensor is adopted to analyze the influence of different excitation modes on performance indexes, such as number of independent measurements, dynamic range of measurements, sensitivity distribution and correlation coefficient of image reconstruction. On the basis of radial rotation angle between the excitation electrodes mapped to the same plane and whether the excitation electrodes are located in the same axial layer, five typical electrode combination modes are designed under dual-electrode excitation and single-electrode measurement protocol. The results show that the variation trend of different indexes influenced by excitation mode is inconsistent. The entropy-based method is applied to comprehensively evaluate the different excitation modes with the selected multiple performance indexes. Among all above modes, the mode in which excitation electrodes are vertically aligned is better universal one. The experimental results show that the position characteristics of the preferable mode can obtain better image reconstruction quality in different distribution models. Furthermore, the better excitation mode will provide guidance for design of other multi-electrode excitation in 3D ET systems with different structures.