基于小波变换的医学图像压缩技术研究

以CT、MRI等医学图像组为对象，研究一种基于小波变换的医学图像数据无失真压缩编码方法。利用小波变换实现图像的多分辨率分解．然后再对变换后的小波图像进行动态Huffman编码。最终实现压缩比较大的图像无失真压缩编码。实验表明．该方法在压缩比和重建图像质量上均达到了较好的性能。     

基于小波变换和似然无偏估计的胃阻抗信号处理研究

目的：介绍一种基于小波变换和似然无偏估计的胃阻抗信号分析去噪的方法。方法：首先经过多分辨分析将信号进行分离，然后应用Stein似然无偏估计对胃阻抗信号进行自适应软阈值去噪处理。结果：实验结果表明，该方法能够有效滤除由呼吸、血流阻抗等因素造成的干扰。结论：小波分析技术为进一步研究胃动力信号的参数分析提供了新途径。     

Automated 3-D registration of MR and CT images of the head

This paper discusses the application of voxel similarity measures in the automated registration of clinically acquired MR and CT data of the head. We describe a novel single-start multi-resolution approach to the optimization of these measures, and the issues involved in applying this to data having a range of different fields of view and sampling resolution. We compare four proposed measures of voxel similarity using the same optimization scheme when presented with 10 pairs of images with a range of initial misregistrations. The registration estimates are compared with those provided by manual point-based registration and evaluated by visual inspection to give an assessment of the robustness and accuracy of the different measures. One full-volume CT image set is used to investigate the performance of each measure when used to align truncated images from different regions in the head. The soft tissue correlation and mutual information measures were found to provide the most robust measures of misregistration, providing results comparable to or better than those from manual point-based registration for all but the most truncated image volumes.     

多分辨率的数字减影图像配准算法

提出基于小波变换的图像配准算法是一种多分辨率匹配算法。该算法可以利用数字减影图像在不同层次上的相似性,配准精度从低至高逐步提高,同时有效地减少运动矢量的搜索复杂度,较好地解决了运算量和检测精度之间的矛盾。该方法被证明是以指数衰减收敛的。整个配准过程在不牺牲配准效果的前提下,提高了匹配速度以及一致性。     

Moment-Based Multi-Resolution HWENO Scheme for Hyperbolic Conservation Laws

In this paper, a high-order moment-based multi-resolution Hermiteweighted essentially non-oscillatory (HWENO) scheme is designed for hyperbolic conservation laws. The main idea of this scheme is derived from our previous work [J.Comput. Phys., 446 (2021) 110653], in which the integral averages of the function andits first order derivative are used to reconstruct both the function and its first orderderivative values at the boundaries. However, in this paper, only the function values atthe Gauss-Lobatto points in the one or two dimensional case need to be reconstructedby using the information of the zeroth and first order moments. In addition, an extramodification procedure is used to modify those first order moments in the troubled-cells, which leads to an improvement of stability and an enhancement of resolutionnear discontinuities. To obtain the same order of accuracy, the size of the stencil required by this moment-based multi-resolution HWENO scheme is still the same as thegeneral HWENO scheme and is more compact than the general WENO scheme. Moreover, the linear weights are not unique and are independent of the node position, andthe CFL number can still be 0.6 whether for the one or two dimensional case, which hasto be 0.2 in the two dimensional case for other HWENO schemes. Extensive numericalexamples are given to demonstrate the stability and resolution of such moment-basedmulti-resolution HWENO scheme.     

Multi-Resolution Method Based on Riemann Solvers for Detonation and Deflagration in High Dimension

In this paper, we propose accurate Riemann solvers for detonation and deflagration with sharp interface in high dimension. The standard finite volume scheme is used for each fluid away from material interface, the detonation and the deflagration interfaces are captured by the level set method, small cut cells are treated with a mixing procedure to get stable algorithm. By Riemann solver for the detonation and the deflagration, the interface fluxes are obtained. With the help of the adaptive multi-resolution algorithms, we extend the method to three dimension conveniently. Numerical examples in two or three-dimension are carried out to demonstrate the potential and robustness of the method.     

基于小波多分辨率系数模值的并发故障检测方法

提出了利用小波分析技术进行信号奇异性检测的多重并发故障检测方法。利用小波多尺度分解技术,将信号进行多尺度的小波分解,得到不同尺度下的信号高频分量的小波系数模值,并根据奇变信号和噪声信号小波系数模值的差异,采用软阈值去噪法,对其高频分量小波系数进行去噪处理,获取不同尺度上突变信号的小波系数模值,实现对故障的检测,并可根据不同尺度上小波系数模值的对应关系,实现对多重并发故障的区分。对电网信号分析的仿真结果证实了该方法的正确性和可行性。     

医学图像的多进制小波分解

主要介绍了多进制小波基本理论并分析了其变换特征,对医学图像做了八进制小波分解,它在医学图像处理中会有更大的应用前景.     

应用Meyer小波消除ECG的基线漂移

目的提出Meyer多分辨率逼近的新方法,消除心电信号基线漂移。方法带基线漂移的心电信号减去其在V9上的正交投影就基本消除了基线漂移。通过多分辨率逼近的数值分析,讨论了小波基的选择,正交投影的选择和数据长度的选择。对目前此类算法因缺少定量化分析方法而难以进行效果的比较,提出算法精度的定量化分析方法,构建算法效果比较的共同基础。结果应用算法于MIT-BIH数据库中具有严重基线漂移的心电数据,采用Meyer小波,带基线漂移的心电信号在V9上的正交投影和基线漂移的差异为(0.3±3.6)μV。结论应用Meyer小波在层次9上消除30 s左右ECG的基线漂移是合适的。     

High Order Finite Difference WENO Methods with Unequal-Sized Sub-Stencils for the Degasperis-Procesi Type Equations

In this paper, we develop two finite difference weighted essentiallynon-oscillatory (WENO) schemes with unequal-sized sub-stencils for solving theDegasperis-Procesi (DP) and $mu$-Degasperis-Procesi ($mu$DP) equations, which containnonlinear high order derivatives, and possibly peakon solutions or shock waves. Byintroducing auxiliary variable(s), we rewrite the DP equation as a hyperbolic-ellipticsystem, and the $mu$DP equation as a first order system. Then we choose a linear finitedifference scheme with suitable order of accuracy for the auxiliary variable(s), andtwo finite difference WENO schemes with unequal-sized sub-stencils for the primalvariable. One WENO scheme uses one large stencil and several smaller stencils, andthe other WENO scheme is based on the multi-resolution framework which uses a series of unequal-sized hierarchical central stencils. Comparing with the classical WENOscheme which uses several small stencils of the same size to make up a big stencil, bothWENO schemes with unequal-sized sub-stencils are simple in the choice of the stenciland enjoy the freedom of arbitrary positive linear weights. Another advantage is thatthe final reconstructed polynomial on the target cell is a polynomial of the same degree as the polynomial over the big stencil, while the classical finite difference WENOreconstruction can only be obtained for specific points inside the target interval. Numerical tests are provided to demonstrate the high order accuracy and non-oscillatoryproperties of the proposed schemes.