鲍威尔和模拟退火优化算法结合的多分辨率三维图像配准

基于互信息的全局配准算法是近年图像配准研究的热点之一，此法具有精度高、鲁棒性强的特点。现将互信息作为相似性测度，采用模拟退火与鲍威尔相结合的多分辨率搜索优化策略，对临床使用的三维CT、MR图像进行了刚体配准。实验结果表明此方法能有效地防止优化陷入局部极值，具有良好的实用性。     

基于互信息医学刚性图像配准方法的研究

目的:基于互信息的配准方法是医学图像配准领域的重要方法,具有鲁棒性,精度高等优点。本文探究医学刚性图像配准的有效算法和关键技术。方法:基于互信息配准方法,利用Powell多参数算法和改进的PV插值算法,得到两幅图像之间的最大互信息和最佳配准参数。结果:二维磨牙CT图像配准实验表明,配准速度快,精度提高,验证了插值方法的有效性。结论:方法和算法可提高配准速度,能有效抑制互信息目标函数的局部极值。     

基于海明窗滤波及粒子群优化搜索的医学图像配准

针对互信息在多模态医学图像配准中的局部极值问题,利用海明窗(Hamming窗)进行滤波预处理,并采用粒子群优化(Particle swarm optimization,PSO)方法搜索配准参数。结果表明,图像经过Hamming窗低通滤波后,局部极值大大减少,有利于利用互信息进行图像的配准。另外,PSO优化算法在大多数情况下都可以收敛到全局最优解。我们提出的方法可有效克服互信息的局部极值问题,并有效提高配准精度。     

基于混合互信息和改进粒子群优化算法的医学图像配准方法

为满足医学图像辅助诊断与治疗的需要,提出一种基于混合互信息和改进粒子群优化算法的医学图像配准方法。在每次迭代时,首先使用基于Renyi熵的改进粒子群优化算法对图像进行全局搜索,再使用基于Shannon熵的Powell算法对当前得到的最优解进行局部寻优。实验图像为60幅模拟图像和10幅临床图像,对70幅图像进行单模态和多模态的医学图像配准实验,所提出算法的单模态医学图像配准结果均达到亚像素级。在多模态医学图像配准实验中,采用5种性能指标,评价配准结果的质量。同3种医学图像配准算法进行比较,结果显示新算法除计算时间外,其他4项指标均为最优,MI指数、NMI指数和CC指数的均值分别为1.338 6、1.363 1和0.837 8。主观和客观分析显示,所提出算法在精确度和收敛速度方面均优越于其他配准算法。     

基于多层次变换和优化方法的PET-CT图像弹性配准

目的为校正PET/CT一体化仪器的误配准和形变问题。方法本文提出一种基于多层次变换和优化的弹性配准方法,以互信息为相似性测度,先进行全局刚性变换使用单纯形优化策略,在刚性变换的基础上使用B样条形变变换并使用有限内存的BFGSB(limited memory Broyden Fietcher Goldfarb Shanno bound,LBFGSB)优化算法。选取3个患者PET/CT联合扫描下的6组数据对本文算法进行验证,并与采用传统单一变换方法和单一优化策略的方法进行了对比。结果采用本文提出的配准算法得到的平均配准时间为19.78 s,平均互信息值为0.3115,较传统仅使用单一变换和单一优化的配准方法在配准速度和精度上有一定的提高。结论基于多层次变换和优化方法的图像配准方法能够较好地解决PET产生的形变问题,配准速度快精度高,可以用来校正PET/CT联合扫描由于呼吸运动和脏器运动产生的误配准和形变问题。     

多模态医学图像配准技术研究

目的:通过对CT和PET图像进行配准实验,得出CT和PET配准的最优插值搜索方法以及粗配准对二者配准结果的影响。方法:首先利用改进的力矩与主轴法对CT和PET图像进行粗配准,得到CT图像的平移量与旋转量。然后针对不同的插值和搜索方法实现互信息配准,并将所得平移量与旋转量作为Powell优化初值进行实验,与使用默认值的Powell优化方法进行对比。结果:实验结果表明:使用双线性插值算法时,两实验的结果基本一致;采用部分体积插值法时,基于粗配准的Powell优化配准效果优于基于默认值的方法;而使用立方卷积插值法时二者配准效果差别不大,但基于粗配准的方法时间更短。结论:基于粗配准的Powell优化方法(部分体积插值与Brent搜索)有更好的配准速度及效果。     

一种基于感兴趣点旋转不变性特征的图像配准新方法

目的:图像配准是图像处理领域重要的研究方向,是图像融合、图像重建和图像分析等研究的基础。在图像配准的主要方法中,基于图像特征的配准方法和基于图像灰度的配准方法各有优缺点,通过结合这两种方法的优点,我们提出了一种基于感兴趣点的旋转不变性特征图像配准的新方法。方法:首先利用Harris角点检测技术,提取模板图像和目标图像的感兴趣点。然后把感兴趣点的旋转不变形特征和灰度值组成图像的特征描述向量,并提出新的代价函数。最后采用分级优化的策略优化代价函数,在配准初期,采用显著的特征点进行配准,以保证配准的速度与鲁棒性,随后通过逐步增加特征点的数量,则保证了配准的精度。结果:为显示本文方法的优越性,实验利用本文方法和基于互信息的B样条方法分别对标准测试图像进行配准,实验结果表明,本文方法较基于互信息的B样条方法在配准精度上有明显提高。结论:本文方法在保持配准鲁棒性的前提下,获得了较高的配准精度。     

基于概率和引力优化模型的医学图像配准

基于互信息的配准方法,其目标函数经常存在许多局部极值,给配准的优化过程带来很大困难。提出一种基于概率模型的引力优化算法,在空间中随机构造参考物体与浮动物体,根据牛顿万有引力定律,搜索空间中质量最大的物体。利用该算法,实现以归一化互信息为相似性测度的医学图像配准实验。实验结果表明,这种方法能够有效地克服互信息的局部极值,在配准精度、配准时间和抗噪性方面都有较好的性能。     

PSO和Powell混合算法在医学图像配准中的应用研究

基于互信息的图像配准方法具有自动化程度高、配准精度高等优点,已被广泛应用于医学图像的配准.但是,基于互信息的目标函数经常是不光滑的,存在许多局部极值,给问题的求解带来了很大的困难.本文讨论了互信息函数的多极值特性,并提出了一种粒子群优化算法(particle swarm optimization,PSO)和Powell混合优化方法.经检验,这种方法能有效地克服互信息函数的局部极值,大大地提高了配准精度,达到亚像素级.     

一种改进的基于互信息的3-D MRI图像配准方法

基于互信息的全局配准算法是近年来图像配准研究的热点之一.该方法具有精度高、鲁棒性强的特点.但目标函数由于插值算法的影响会陷入局部极值,引起误配准.本文实现了一种结合图像滤波预处理进行插值计算的方法,得到更加平滑的目标函数,有效的克服了"插值假像"问题.对标准数据库中的3-D MRI图像进行了刚性配准,实验结果表明该配准方法具有较高的精确度,具有很强的实用性.     

Non-rigid image registration using a median-filtered coarse-to-fine displacement field and a symmetric correlation ratio

Conventional approaches to image registration are generally limited to image-wide rigid transformations. However, the body and its internal organs are non-rigid structures that change shape due to changes in the body's posture during image acquisition, and due to normal, pathological and treatment-related variations. Inter-subject matching also constitutes a non-rigid registration problem. In this paper, we present a fully automated non-rigid image registration method that maximizes a local voxel-based similarity metric. Overlapping image blocks are defined on a 3D grid. The transformation vector field representing image deformation is found by translating each block so as to maximize the local similarity measure. The resulting sparsely sampled vector field is median filtered and interpolated by a Gaussian function to ensure a locally smooth transformation. A hierarchical strategy is adopted to progressively establish local registration associated with image structures at diminishing scale. Simulation studies were carried out to evaluate the proposed algorithm and to determine the robustness of various voxel-based cost functions. Mutual information, normalized mutual information, correlation ratio (CR) and a new symmetric version of CR were evaluated and compared. A T1-weighted magnetic resonance (MR) image was used to test intra-modality registration. Proton density and T2-weighted MR images of the same subject were used to evaluate inter-modality registration. The proposed algorithm was tested on the 2D MR images distorted by known deformations and 3D images simulating inter-subject distortions. We studied the robustness of cost functions with respect to image sampling. Results indicate that the symmetric CR gives comparable registration to mutual information in intra- and inter-modality tasks at full sampling and is superior to mutual information in registering sparsely sampled images.     

Non-rigid registration between 3D ultrasound and CT images of the liver based on intensity and gradient information

In order to utilize both ultrasound (US) and computed tomography (CT) images of the liver concurrently for medical applications such as diagnosis and image-guided intervention, non-rigid registration between these two types of images is an essential step, as local deformation between US and CT images exists due to the different respiratory phases involved and due to the probe pressure that occurs in US imaging. This paper introduces a voxel-based non-rigid registration algorithm between the 3D B-mode US and CT images of the liver. In the proposed algorithm, to improve the registration accuracy, we utilize the surface information of the liver and gallbladder in addition to the information of the vessels inside the liver. For an effective correlation between US and CT images, we treat those anatomical regions separately according to their characteristics in US and CT images. Based on a novel objective function using a 3D joint histogram of the intensity and gradient information, vessel-based non-rigid registration is followed by surface-based non-rigid registration in sequence, which improves the registration accuracy. The proposed algorithm is tested for ten clinical datasets and quantitative evaluations are conducted. Experimental results show that the registration error between anatomical features of US and CT images is less than 2 mm on average, even with local deformation due to different respiratory phases and probe pressure. In addition, the lesion registration error is less than 3 mm on average with a maximum of 4.5 mm that is considered acceptable for clinical applications.     

Spatio-temporal (2D+T) non-rigid registration of real-time 3D echocardiography and cardiovascular MR image sequences

In this paper we describe a method to non-rigidly co-register a 2D slice sequence from real-time 3D echocardiography with a 2D cardiovascular MR image sequence. This is challenging because the imaging modalities have different spatial and temporal resolution. Non-rigid registration is required for accurate alignment due to imprecision of cardiac gating and natural motion variations between cardiac cycles. In our approach the deformation field between the imaging modalities is decoupled into temporal and spatial components. First, temporal alignment is performed to establish temporal correspondence between a real-time 3D echocardiography frame and a cardiovascular MR frame. Spatial alignment is then performed using an adaptive non-rigid registration algorithm based on local phase mutual information on each temporally aligned image pair. Experiments on seven volunteer datasets are reported. Evaluation of registration errors based on expert-identified landmarks shows that the spatio-temporal registration algorithm gives a mean registration error of 3.56 ± 0.49 and 3.54 ± 0.27 mm for the short and long axis sequences, respectively.     

引入高斯函数的互信息法多模态图像配准

目的：最大互信息作为相似度测量在医学图像配准中已被广泛应用。在计算图像互信息时,为了避免引入新的灰度值一般采用部分体积插值统计两幅图像的联合直方图。但用该方法计算中,当图像平移整数点时,统计联合直方图会出现缺陷,使目标函数出现局部极值,从而造成误配准。方法：将高斯函数引入到直方图统计中,选取适当的邻域,用高斯函数计算邻域内各点像素对联合直方图的贡献。利用高斯函数的平滑性,避免了在互信息计算过程中统计图像联合直方图时出现误差。使用Powell优化方法,寻找最佳的优化参数,实现图像的最佳配准。结果：采用CT-PET数据进行实验,该方法平滑了目标函数,有效地消除了局部极值,提高了多模态图像配准的精确性,并且,对噪音图像配准也产生很好的效果。结论：该方法适用于多模态医学图像配准,克服了传统互信息计算时的不足,提高了配准的正确率和精确度。     

基于互信息的医学图像配准实验

基于互信息的配准方法，包括互信息和归一化互信息方法，是目前医学图像配准中无创、自动且精度很高的一种方法。已经被广泛应用。但是在其目标函数中存在着一定程度的幅值振荡现象。特别是在单模态图像配准中。我们研究发现，产生这种振荡的原因除了插值赝像外，还有由配准过程中图像重叠部分发生变化而引起的熵的变化不确定性。由插值赝像所带来的振荡基本上可以被消除掉；由熵的变化不确定性所带来的振荡很难被消除，但是这种振荡作用在归一化互信息中影响不大。归一化互信息比互信息具有更高的稳健性，适合于更广的应用范围。     

磁共振弥散张量成像几何畸变的三维校准

采用图像非刚体配准的方法校正磁共振弥散张量成像的几何畸变.在3D数据场中,采用仿射变换和B样条的变形配准方法来矫正几何畸变,配准的相似性测度采用互信息为准则.弥散张量成像特定组织间的磁女感性差异引起的几何畸变得到了一定纠正,所采用的方法对畸变有一定的抑制.采用3D配准的方法可以对弥文张量成像的几何畸变进行纠正,明显提高了图像质量.     

基于互信息的多分辨率三维脑图像配准方法

在3D多模医学图像的配准方法中，最大互信息法精度高，鲁棒性强，使用范围广，本文将归一化互信息作为相似性测度，采用不同的采样范围和采样子集，使用Powell多参数优化法和Brent一维搜索算法对3DCT，MR和PET脑图像进行了刚体配准，为了加快配准速度，使用了多分辨的金字塔方法，对PET图像采用基于坐标的阈值选取方法对图像进行分割预算法，消除了大部分放射状背景伪影，美国万德贝尔大学对结果进行的评估证明配准精度可达亚体元级。     

Rigid 2D/3D slice-to-volume registration and its application on fluoroscopic CT images

Registration of single slices from FluoroCT, CineMR, or interventional magnetic resonance imaging to three dimensional (3D) volumes is a special aspect of the two-dimensional (2D)/3D registration problem. Rather than digitally rendered radiographs (DRR), single 2D slice images obtained during interventional procedures are compared to oblique reformatted slices from a high resolution 3D scan. Due to the lack of perspective information and the different imaging geometry, convergence behavior differs significantly from 2D/3D registration applications comparing DRR images with conventional x-ray images. We have implemented a number of merit functions and local and global optimization algorithms for slice-to-volume registration of computed tomography (CT) and FluoroCT images. These methods were tested on phantom images derived from clinical scans for liver biopsies. Our results indicate that good registration accuracy in the range of 0.50 and 1.0 mm is achievable using simple cross correlation and repeated application of local optimization algorithms. Typically, a registration took approximately 1 min on a standard personal computer. Other merit functions such as pattern intensity or normalized mutual information did not perform as well as cross correlation in this initial evaluation. Furthermore, it appears as if the use of global optimization algorithms such as simulated annealing does not improve reliability or accuracy of the registration process. These findings were also confirmed in a preliminary registration study on five clinical scans. These experiments have, however, shown that a strict breath-hold protocol is inevitable when using rigid registration techniques for lesion localization in image-guided biopsy retrieval. Finally, further possible applications of slice-to-volume registration are discussed.