Non-Rigid Medical Image Registration with Joint Histogram Estimation Based on Mutual Information

A mutual information-based non-rigid medical image registration algorithm is presented. An approximate function of Hanning windowed sinc is used as kernel function of partial volume (PV) interpolation to estimate the joint histogram, which is the key to calculating the mutual information. And a new method is proposed to compute the gradient of mutual information with respect to the model parameters. The transformation of object is modeled by a free-form deformation (FFD) based on B-splines. The experiments on 3D synthetic and real image data show that the algorithm can converge at the global optimum and restrain the emergency of local extreme.

Relaxation labeling for non-rigid point matching under neighbor preserving

Non-rigid point matching has received more and more attention.Recently,many works have been developed to discover global relationships in the point set which is treated as an instance of a joint distribution.However,the local relationship among neighboring points is more effective under non-rigid transformations.Thus,a new algorithm taking advantage of shape context and relaxation labeling technique,called SC-RL,is proposed for non-rigid point matching.It is a strategy that joints estimation for correspondences as well as the transformation.In this work,correspondence assignment is treated as a soft-assign process in which the matching probability is updated by relaxation labeling technique with a newly defined compatibility coefficient.The compatibility coefficient is one or zero depending on whether neighboring points preserving their relative position in a local coordinate system.The comparative analysis has been performed against four state-of-the-art algorithms including SC,ICP,TPS-RPM and RPM-LNS,and the results denote that SC-RL performs better in the presence of deformations,outliers and noise.

Non-rigid registration and KLT filter to improve SNR and CNR in GRE-EPI myocardial perfusion imaging

The purpose of the study was to evaluate the effect of motion compensation by non-rigid registration combined with the Karhunen-Loeve Transform (KLT) filter on the signal to noise (SNR) and contrast-to-noise ratio (CNR) of hybrid gradient-echo echoplanar (GRE-EPI) first-pass myocardial perfusion imaging. Twenty one consecutive first-pass adenosine stress perfusion MR data sets interpreted positive for ischemia or infarction were processed by non-rigid Registration followed by KLT filtering. SNR and CNR were measured in abnormal and normal myocardium in unfiltered and KLT filtered images following nonrigid registration to compensate for respiratory and other motions. Image artifacts introduced by filtering in registered and nonregistered images were evaluated by two observers. There was a statistically sig- nificant increase in both SNR and CNR between normal and abnormal myocardium with KLT filtering (mean SNR increased by 62.18% ± 21.05% and mean CNR increased by 58.84% ± 18.06%;p = 0.01). Motion correction prior to KLT filtering reduced significantly the occurrence of filter induced artifacts (KLT only-artifacts in 42 out of 55 image series vs. registered plus KLT-artifacts in 3 out of 55 image series). In conclusion the combination of non-rigid registration and KLT filtering was shown to increase the SNR and CNR of GRE-EPI perfusion images. Subjective evaluation of image artifacts revealed that prior motion compensation significantly reduced the artifacts introduced by the KLT filtering process.

Experiment and numerical simulation on the characteristics of fluid–structure interactions of non-rigid airships

Fluid-structure interaction is an important issue for non-rigid airships with inflated envelopes. In this study, a wind tunnel test is conducted, and a loosely coupled procedure is correspondingly established for numerical simulation based on computational fluid dynamics and nonlinear finite element analysis methods. The typical results of the numerical simulation and wind tunnel experiment, including the overall lift and deformation, are in good agreement with each other. The results obtained indicate that the effect of fluid-structure interaction is noticeable and should be considered for non-rigid airships. Flow- induced deformation can further intensify the upward lift force and pitching moment, which can lead to a large deformation. Under a wind speed of 15 m/s, the lift force of the non-rigid model is increased to approximatelv 60% compared with that of the rigid model under a high angle of attack.

Non-limit passive soil pressure on rigid retaining walls

This paper aims to reveal the depth distribution law of non-limit passive soil pressure on rigid retaining wall that rotates about the top of the wall(rotation around the top(RT) model). Based on Coulomb theory, the disturbance degree theory, as well as the spring-element model, by setting the rotation angle of the wall as the disturbance parameter, we establish both a depth distribution function for sand and a nonlinear depth distribution calculation method for the non-limit passive soil pressure on a rigid retaining wall under the RT model, which is then compared with experiment. The results suggest that under the RT model: the non-limit soil pressure has a nonlinear distribution; the backfill disturbance degree and the lateral soil pressure increase with an increase in the wall rotation angle; and, the points where the resultant lateral soil pressure acts on the retaining wall are less than 2/3 of the height of the wall. The soil pressure predicted by the theoretical calculation put forward in this paper are quite similar to those obtained by the model experiment, which verifies the theoretical value, and the engineering guidance provided by the calculations are of significance.

Spectral Distance Distributions for Non-rigid Objects

Non-rigid shape deformation without tearing or stretching is called isometry. There are many difficulties to research non-rigid shape in Euclidean space. Therefore, non-rigid shapes are firstly embedded into a none-Euclidean space. Spectral space is chosen in this paper. Then three descriptors are proposed based on three spectral distances. The existence of zero-eigenvalue has negative effects on computation of spectral distance, Therefore the spectral distance should be computed from the first non-zcro-eigenvalue. Experiments show that spectral distance distributions are very effective to describe the non-rigid shapes.

Non-Rigid Image Registration Algorithm Based on B-Splines Approximation

An intensity-based non-rigid registration algorithm is discussed, which uses Gaussian smoothing to constrain the transformation to be smooth, and thus preserves the topology of images. In view of the insufficiency of the uniform Gaussian filtering of the deformation field, an automatic and accurate non-rigid image registration method based on B-splines approximation is proposed. The regularization strategy is adopted by using multi-level B-splines approximation to regularize the displacement fields in a coarse-to-fine manner. Moreover, it assigns the different weights to the estimated displacements according to their reliabilities. In this way, the level of regularity can be adapted locally. Experiments were performed on both synthetic and real medical images of brain, and the results show that the proposed method improves the registration accuracy and robustness.

MUTUAL INFORMATION BASED 3D NON-RIGID REGISTRATION OF CT/MR ABDOMEN IMAGES

A mutual information based 3D non-rigid registration approach was proposed for the registration of deformable CT/MR body abdomen images. The Parzen Windows Density Estimation (PWDE) method is adopted to calculate the mutual information between the two modals of CT and MRI abdomen images. By maximizing MI between the CT and MR volume images, the overlapping part of them reaches the biggest, which means that the two body images of CT and MR matches best to each other. Visible Human Project (VHP) Male abdomen CT and MRI Data are used as experimental data sets. The experimental results indicate that this approach of non-rigid 3D registration of CT/MR body abdominal images can be achieved effectively and automatically, without any prior processing procedures such as segmentation and feature extraction, but has a main drawback of very long computation time.

Analysis and optimization of assembly variations for non-rigid parts

Traditional variation analysis methods are not applicable to non-rigid assemblies due to possible part deformation during the assembly process. This paper presents the use of finite element methods to simulate assembly deformation. The relationship between the parts’ variation and the variation of the key points in final assembly for quality control is set up by calculating the spring back deformation after assembly. Moreover, the optimization method for non-rigid assembly variations based on finite element analysis is presented. The optimal objective is to reduce the manufacturing cost. The approach is implemented by using ANSYS and MATLAB. The test example shows that the proposed method is effective and applicable.

Real-time Animation Technique for a Kind of Non-rigid Objects

A real-time animation technique for a kind of non-rigid objects, flexible and thin objects, is proposed, which can update with stability the state of n mass points of the mass-spring (MS) model with time complexity of O(n). The new implicit numerical integration technique of the authors, which is based on a simple approximation of the linear system, has great advantages over the existing implicit integration methods. Moreover, experiment shows that the new technique is highly efficient in animating a kind of non-rigid objects, and suitable for the draping module of the 3D garment CAD system.

Computing the Full Non-Rigid Group of Trimethylborane and Cyclohaxane Using Wreath Product

This paper computes the group and character table of Trimethylborane and Cyclohaxane. Results show that the groups are isomorphic to the wreath products C3wrC2 and C2wrC6 with orders 81 and 384 and with 17 and 28 conjugacy classes respectively, where Cn denotes a cyclic group of order n.

Dynamic modeling and simulation for the rigid flexible coupling system with a non-tip mass

The rigid flexible coupling system with a mass at non-tip position of the flexible beam is studied in this paper. Using the theory about mechanics problems in a non-inertial coordinate sys- tem, the dynamic equations of the rigid flexible coupling system with dynamic stiffening are estab- lished. It is clearly elucidated for the first time that, dynamic stiffening is produced by the coupling effect of the centrifugal inertial load distributed on the beam and the transverse vibration deformation of the beam. The modeling approach in this paper successfully solves problems of popular modeling methods nowadays： the derivation process is too complex by using only one dynamic principle; a clearly theoretical mechanism for dynamic stiffening can＇ t be offered. First, the mass at non-tip po- sition is incorporated into the continuous dynamic equations of the system by use of the Dirac lunch tion and the Heaviside function. Then, based on the conclusions of orthogonalization about the nor- mal constrained modes, the finite dimensional state space equations suitable for controller design are obtained. The numerical simulation results show that： dynamic stiffening is included in the first-or- der model established in this paper, which indicates the dynamic responses of the rigid flexible cou- pling system with large overall motion accurately. The results also show that the mass has a soften- ing effect on the dynamic behavior of the flexible beam, and the effect would be more obvious when the mass has a larger mass, or lies closer to the tip of the beam.

Non-rigid 3D models retrieval based on hierarchical matching

In 3D models retrieval, feature description and retrieval of non-rigid model face more complex problems due to the isometry transformation of itself. We introduce the hierarchical combination matching into the feature comparison, and build a map between the divided regions of two models, and then achieve accurate feature matching based on patch-by-patch, which successfully introduces the spatial information into feature matching. Verified by experiment, the 3D model retrieval method proposed in this paper based on hierarchical combination matching can make sure more accurate feature matching, so as to enhance the precision of retrieval.

基于非刚性特征的发动机积碳程度判别模型

汽车发动机积碳的长期累积会引起发动机动力下降、油耗上升、排放性能降低等问题,对发动机及时的检测和清理可以有效缓解积碳造成的影响。本文提出了一种新的基于非刚性特征的模型,用于积碳程度的判别。首先,在模型中使用可变形卷积调整卷积核的偏移位置和偏移幅度,提高网络的有效感受野,提取非刚性特征信息;其次,根据核区域中像素的相关性,使用自适应指数度量池化核对神经元进行加权,以此捕获更好的细节特征信息;最后,添加基于自注意机制的特征增强模块,获取特征图的上下文信息。经过实验测试,本文方法的测试准确率为87.1%,各项指标相较原始模型平均提高2.5%,证明本文方法可以提取有效的积碳程度判别特征。

优化谱对齐的三维模型簇一致性对应关系计算

为了解决非刚性三维模型簇对应关系计算准确率低、一致性差,且难以实现双射的问题,提出了一种采用优化谱对齐算法和规范一致潜在基的非刚性三维模型簇对应关系计算新方法。首先,利用函数映射的伴随算子实现模型间谱域信息的对齐,计算模型簇中每个模型对的函数映射矩阵,解决函数映射与逐点映射方向不一致的问题;其次,使用改进的模型映射集合算法为每个模型对的函数映射矩阵赋予相应权重,降低初始化参数的噪声对模型簇对应关系计算结果的影响;最后,在模型簇的对应关系计算过程中加入极限模型的规范一致潜在基,极限模型可以看成模型簇中所有模型的类型结构,是一个具有几何可变性的中间模型,提高算法的一致性和双射性。实验结果表明:与已有算法相比,本算法在FAUST、SCAPE、TOSCA和SHERC’16 Topology数据集上构建的对应关系测地误差最小,能够减少初始化参数的噪声,解决模型自身对称性影响对应关系计算的问题,更加精确地构建出具有一致性和双射性的非刚性三维模型簇对应关系。

时序特征图像配准算法的抗噪性分析

提出了一种基于时序特征变化的图像配准算法,通过时序灰度特征的分析和提取,实现了可见光与红外非固形动态目标图像的有效配准。重点分析了该算法的抗噪能力,当噪声对配准精度产生明显影响时,设计了一种预处理滤波方法,通过减小噪声项在时序特征提取中的影响,从而降低了算法的误配率。利用蜡烛火焰作为探测目标,通过实验表明,在图像信噪比为10 dB的情况下该算法的抗噪性较好,能够实现非固形目标的可见光与红外图像配准。当目标图像信噪比等于6 dB时,该算法就无法完成图像配准,此时采用预处理滤波方法,算法的误配率得以降低,能成功实现非固形目标的可见光与红外图像配准。实验中计算得到预处理方法的关键参数m取0.25时效果最好。

基于局部归一化互信息联合约束的三维头颈部CT/MR配准方法

针对头颈部图像的复杂解剖结构和不同模态图像的差异,提出一种改进的多模态配准方法。该方法采用局部归一化互信息作为相似性测度,以捕捉局部图像区域的相似性,并减少不同区域间的强度差异对配准结果的影响。此外,为解决MR图像易受到噪声和伪影的影响产生畸变的问题,引入F范数约束配准过程,抑制不必要的畸变。实验结果表明,所提方法在降低均方误差、提高配准精度和鲁棒性方面均有所提高。

带柔性部件飞行器刚性耦合系数矩阵优化算法

针对目前飞行器刚性耦合系数矩阵算法中按照单元节点规律排列的质量矩阵数据处理难度大,运算维度高的问题,本文提出一种非离散化方法的刚性耦合系数矩阵优化算法,利用在三维模型中可以直接获取的柔性部件质量特性,替代高维度的质量矩阵参与计算,避免了模型离散化误差,在简化刚性耦合系数计算流程的同时,具有提高计算结果准确度的效果,增强了工程设计中的便利性.

基于局部高斯分布模型的图像配准方法

提出了一种基于统计和变分相结合的非刚体图像配准新模型。假设残差图像服从具有不同均值和方差的局部高斯分布,由此得到一个双重能量泛函,再结合变分的正则化方法,得到了一种配准新模型。该方法的新颖之处在于,保真项中引入了权重函数和一些控制参数。其中权重函数可以自动有效地区分残差图像中灰度对比度不同的区域,控制参数的引入提高了算法的鲁棒性。合成图像、二维肺部CT及三维大脑MRI图像的配准结果证明了这一方法的有效性和准确性。

手机点胶三维轨迹生成方法

智能手机边框在制造过程中往往存在形变问题,先前的视觉定位方法难以得到精确的边框点胶位置。针对此问题,提出了一种新颖的手机点胶三维轨迹生成方法。首先,使用三维线激光测量仪扫描边框,引入基于位姿图的点云拼接算法解决边框点云的拼接问题。采用基于模板的方法,标注模板点胶轨迹。然后,通过基于变形图的非刚性配准算法将模板与目标边框对齐,得到变换后的轨迹,并提出轨迹优化策略生成精准的目标点胶轨迹。实验证明,所提方法生成的轨迹精度可达0.01 mm以下,且速度可达到在线实时测量效果。