基于小波变换的分数阶微分算法在肝脏肿瘤CT图像纹理增强中的应用

图像纹理增强过程中容易丢失平滑区域纹理细节，而分数阶微分增强虽然能够非线性保留平滑区域纹理细节，但对频率分辨率敏感。针对这个问题，提出一种基于小波变换的分数阶微分纹理增强算法，应用于平扫计算机断层扫描（CT）图像的肝脏肿瘤区域的纹理增强。首先，通过小波变换将图像感兴趣区分解成多个子带分量；其次，基于分数阶微分定义构造一个带补偿参数的分数阶微分掩膜；最后，使用该掩膜与每个高频子带分量进行卷积并利用小波逆变换重组图像感兴趣区。实验结果表明，该方法在使用较大分数阶次显著增强肿瘤区域的高频轮廓信息的同时，有效地保留了低频平滑的纹理细节：增强后的肝细胞癌区域与原区域相比，信息熵平均增加36.56%，平均梯度平均增加321.56%，平均绝对差值平均为9.287；增强后的肝血管瘤区域与原区域相比，信息熵平均增加48.77%，平均梯度平均增加511.26%，平均绝对差值平均为14.097。     

Sparsity-inspired image reconstruction for electrical capacitance tomography

We present a new image reconstruction method for Electrical Capacitance Tomography (ECT). ECT image reconstruction is generally ill-posed because the number of measurements is small whereas the image dimensions are large. Here, we present a sparsity-inspired approach to achieve better ECT image reconstruction from the small number of measurements. Our approach for ECT image reconstruction is based on Total Variation (TV) regularization. We apply an efficient Split-Bregman Iteration (SBI) approach to solve the problem. We also propose three metrics to evaluate image reconstruction performance, i.e., a joint metric of positive reconstruction rate (PRR) and false reconstruction rate (FRR), correlation coefficient, and a shape and location metric. The results on both synthetic and real data show that the proposed TV-SBI method can better preserve the edges of images and better resolve different objects within reconstructed images, as compared to a representative state-of-the-art ECT image reconstruction algorithm, Projected Landweber Iteration with Linear Back Projection initialization (LBP-PLI).     

弹性波衍射CT

本文直接从等价于弹性动力学Ｎａｖｉｅｒ方程的耦合齐次与非齐次矢量波动方程组出发，围绕弹性波衍射ＣＴ展开了理论研究，尤其是其非齐次方程含有震源项，同时适合Ｐ波和Ｓ波，考虑爆炸震源，引进塑性半径，运用张量运算，推导了Ｂｏｒｎ近似下散射波谱与目标函关系，得到二种数据采集方式下的层析成像ＦＢＰ公式，可同时适用于Ｐ波和Ｓ波，尽管与以往不涉及震源项的结果相似，但本结果更符合地震勘探情况。     

JaTS: a fully portable seismic tomography software based on Fresnel wavepaths and a probabilistic reconstruction approach

JaTS, a Java 2D seismic tomography software, is presented. It implements original algorithms achieving optimal accuracy with reasonable computing costs. A second-order Fast Marching Method (FMM) is used for solving the eikonal equation, therefore enabling a fast and robust computation of seismic traveltimes between sources and receivers. The wavepaths are materialized by Fresnel volumes rather than by conventional rays. This approach accounts for complex velocity models and has the advantage of considering the effects of the wave frequency in the velocity model resolution. The model is computed by a Simultaneous Iterative Reconstruction Technique (SIRT) which has been reformulated to integrate Fresnel wavepaths by using a probabilistic approach. In addition, various utilities are implemented, such as a tapering filter, used to decrease artifact effects occurring in the vicinity of the sources and receivers. The software also offers the possibility of reconstructing the velocity field on a grid larger than the one used for the wave propagation computation. This contributes to stabilize the estimated values. All of the seismic processing tools have been integrated with a user-friendly graphical interface. JaTS represents a tightly integrated tool suite that supports the entire process of importing the SG2 field records, first-break picking, forward modeling and velocity-field computing across multiple platforms.     

A snake for model-based segmentation of biomedical images

In this work we present a snake based approach for the segmentation of images of computerized tomography (CT) scans. We introduce a new term for the internal energy and another one for external energy which solve common problems associated with classical snakes in this type of images. A simplified minimizing method is also presented.     

基于最大后验概率的熔融态物料结构的层析图像提取法

以聚合物挤出过程中的熔融态物料为对象，在比较层析图像与反射式光强图像的成像特点基础上，叙述了基于最大后验概率的熔融态物料多特征结构的层析图像提取方法，并介绍了层析图像提取实验的结果，理论与实验表明，该方法能有效地分割熔融态物料，细化熔融态结构,实现对熔融态物料特征结构的提取和测量。     

用于复合材料缺陷可视化检测的l_1正则化算法

随着复合材料在民用飞机中越来越广泛的应用,复合材料缺陷的在线检测对无损检测技术提出了更高要求。为提高平面电容层析成像(ECT)系统的成像质量,从而提高其对复合材料缺陷的检测精度,对基于l1正则化的成像算法进行了研究。采用交替最小化方法进行数值计算,并结合迭代阈值法,对重建图像进行降噪。试验结果表明,与ECT中常用的Landweber、Tikhonov正则化等算法相比,该方法能够有效分辨物场中的不同介质,提高了成像质量和被测物体边缘分辨率。     

基于电磁层析成像技术的接地网导体异常检测

接地网是维护系统安全、保障运行人员及设备安全的重要环节,对其异常状态的有效检测直接关系到电力系统的安全稳定运行.文中研究了基于电磁层析成像(Electromagnetic Tomography,EMT)技术的接地网导体异常状态检测方法,应用改进Landweber迭代算法基于EMT技术测试系统的感应电压测量结果获取了接地网导体的重建图像,定义了图像相关系数对接地网导体的异常状态进行检测.对某35 kV接地网正常与腐蚀、断裂等典型故障下的分析结果表明,将EMT计算引入接地网导体的异常检测具有一定的可行性,且具有非接触、对接地网导体状态变化敏感等优势,所定义的图像相关系数指标能有效识别接地网导体的异常状态.研究结果可为接地网运行状态的准确评估提供重要依据.     

开放式电阻抗成像中数字相敏检波器设计

开放式电阻抗成像技术对测量系统的精度要求很高,为此研制了基于FPGA的数字相敏检波器(DPSD)以用于电阻抗成像的数据测量。通过分析DPSD的信号采集与计算原理,给出了关键参数的计算,基于DDS技术的ADC时钟设计方法。同时设计了高速多通道ADC转换电路,低抖动性能的ADC时钟电路、FPGA实现实时数字相敏检波的计算方法,提高了系统的信噪比。经实验测试表明,在1KHz~1MHz正弦信号注入频率的条件下,系统的信噪比最高可达104dB,精度高,稳定度好。