Shear strain estimation and lesion mobility assessment in elastography

Elastography typically measures and images the normal strain component along the insonification/compression axis, i.e., in the axial direction. We have recently shown that, by using interpolation and cross-correlation methods of transversely displaced RF echo segments, it is possible to measure and image displacement and strain transversely to the beam with good precision. This enables the estimation and imaging of all three principal normal strain components. Generally, motion in a direction other than that in which strain is estimated may result in decorrelation noise, severely corrupting the estimates. Therefore, a correction method is applied to correct the displacement and strain estimates for decorrelating motion. In this paper, we show how corrected displacement estimates can also be used to estimate and image the shear strain components. This may allow us to identify regions of decorrelation noise in the normal strain measurement that are due to shear strain. Shear strain estimates provide supplementary information, which can characterize different tissue elements based on their mobility. In the case of breast lesions, low mobility is related to malignancy. Following an in vivo case, we show with 2D simulations how assessment of tumor mobility can be achieved with shear strain estimation.     

Determining displacement and strain maps immune from aliasing effect with the grid method

Spatial aliasing may affect methods based on grid image processing to retrieve displacement and strain maps in experimental mechanics. Such methods aim at estimating these maps on the surface of a specimen subjected to a loading test. Aliasing, which is often not noticeable to the naked eye in the grid images, may give spurious fringes in the strain maps. This paper presents an analysis of aliasing in this context and provides the reader with simple guidelines to minimize the effect of aliasing on strain maps extracted from grid images.     

Three-dimensional myocardial strain analysis based on short- and long-axis magnetic resonance tagged images using a 1D displacement field

A robust algorithm to estimate three-dimensional strain in the left-ventricular heart wall, based on magnetic resonance (MR) grid-tagging in two sets of orthogonal image planes, is presented. Starting-point of this study was to minimize global interpolation and smoothing. Only the longitudinal displacement was interpolated between long-axis images. Homogeneous strain analysis was performed using small tetrahedrons. The method was tested using a stack of short-axis images and three long-axis images in six healthy volunteers. In addition, the method was subjected to an analytical test case, in which the effect of noise in tag point position on the observed strains was explored for normally distributed noise (0.5 mm RMS). In volunteers, the error in the longitudinal displacement due to interpolation between the long-axis image planes was -0.10 +/- 0. 48 mm (mean +/- SD). The resulting error in the longitudinal strain epsilon(l) was -0.003 +/- 0.02. The analytical test case was used to quantify the effects of three sources of errors on the observed strain. The SD of the difference between homogeneous strain and true strain was 0.06 for epsilon(r.) The error due to the 3-D reconstruction was 0.004 for epsilon(r.) The error in epsilon(r) resulting from simulated noise in the tag point position was 0.10. Equivalent results were obtained for all other strain parameters; thus, the error resulting from noise in the tag point position dominates the error introduced by approximations in the method. Because the proposed method uses a minimum of global interpolation and smoothing, it offers the prospect to detect small regions of aberrant contraction.     

一种胶片式的静态光学目标模拟器

光学成像敏感器是卫星姿态控制分系统的重要组成部分，用于月面景象的获取，可为月面着陆器完成障碍识别、路径规划和安全区域选取等功能提供图像信息来源。为实现光学成像敏感器装星后设备功能和性能的检测，需要一种可在室内为光学成像敏感器提供月面场景信息的光学仪器。设计和研制了一种胶片式的静态光学目标模拟器，该目标模拟器以胶片作为图像源，通过积分球均匀照明系统将胶片照亮，并经由光学镜头将胶片图像投射至无穷远处，从而供光学成像敏感器接收。设计完成的静态光学目标模拟器视场≥30°×30°，入瞳直径Φ5 mm，入瞳距离为41 mm，镜头焦距44.78 mm，图像像素分辨率≤1 024×1 024，各项指标均达到了光学成像敏感器装星后光闭路试验的要求。     

Generation of Realistic Infrared Image for Moving Objects

Most of current methods are available for synthesizing the static infrared scene, but fail to simulate the infrared signature of the objects caused by motion. This paper presents a new method for generating realistic infrared image of moving objects. Considering various environmental factors, object geometry and structure, internal heat conditions and state of movement, an infrared image synthesis model for moving objects is established. Based on this model the rendering method for infrared image of this kind of objects is proposed. By incorporating the effect of atmosphere transmission and the noise mechanism of infrared sensor, the infrared images of the working aircraft and automobile are successfully generated from different viewpoint. Experimental results illustrate the potential of our method.     

Noise in superresolution reconstruction

Recently there has been a significant interest in reconstructing a high-resolution (HR) image based on a set of low-resolution (LR) images with relative displacement. These images are typically undersampled with respect to the image spectrum of a HR image. I show that, although ideally a resolution increase of N times is possible with N LR images, in a practical system noise is a limiting factor that increases substantially as we approach this theoretical superresolution limit. For one dimension and a special case with two LR images, I present an analytical result of the noise amplification as a function of their displacement. This is defined as a condition number of the superresolution system, with the associated definitions of a well-conditioned and ill-conditioned superresolution reconstruction system.     

Dynamic strain measurement using two wavelength-matched fiber Bragg grating sensors interrogated by a cascaded long-period fiber grating

In this work, we describe a fiber Bragg grating (FBG) sensing system using two wavelength-matched FBG sensors for static and dynamic strain measurement. A cascaded long-period fiber grating (CLPG)-based demodulation technique has been used to interrogate the two wavelength-matched FBG sensors. Experimental results of static strain measurement show that the proposed system has a strain resolution of 1 με. This system has also been used for dynamic strain measurement. An eddy current displacement meter-based system has been used as a comparison measurement. Experimental results of dynamic strain measurement have proved that the FBG sensing system has a good performance in the measurement of dynamic strain. The results of static and dynamic strain measurement indicate that the sensing system using two wavelength-matched FBG sensors is superior to the single FBG sensor system.     

用于MR图像非局域均值去噪的边缘增强策略

非局域均值(NLM)滤波有很好的去噪效果并已成功地应用于磁共振图像的去噪中,但与所有去噪方法相同,总是会在一定程度上模糊图像细节. 该文提出将从原始图像中提取出来的高频信息与NLM去噪图像相融合,来还原在去噪过程中丢失的细节. 首先利用一种基于拉普拉斯金字塔的多分辨率方法,从原始图像中提取出包含丰富的边缘信息的高频组分. 然后利用作者提出的一种新的基于SUSAN算子的边缘检测算子产生一幅连续的边缘图,并利用该边缘图将高频组分与NLM方法去噪的图像相融合. 该方法在图像的平滑区域取得了良好的去噪效果,同时可以保留甚至增强图像的细节. 同时,该方法对图像的增强不会导致增强图像中常见的伪影.     

Quality of images decrypted from in-line holographic encryption of images

We investigate quality of images decrypted from in-line holograms recorded with a random phase mask placed behind an input image. High- and low-contrast fingerprint images are used as test scenes. The simulation results show that due to multiple convolution processes and a limitation of the CCD sensor resolution, quality of decrypted images is sensitive to spatial separations between the input image, the phase mask and the hologram. We propose a new method for improving quality of decrypted images by using background noise removal. It is found that in comparison with high-contrast input, the low-contrast image is more robust to distortion caused by the encryption–decryption process.     

A 128 × 128 Pixel Complementary Metal Oxide Semiconductor Image Sensor with an Improved Pixel Architecture for Detecting Modulated Light Signals

A complementary metal oxide semiconductor (CMOS) image sensor for the detection of modulated light under background illumination has been developed. When an object is illuminated by a modulated light source under background illumination the sensor enables the object alone to be captured. This paper describes improvements in pixel architecture for reducing fixed pattern noise (FPN) and improving the sensitivity of the image sensor. The improved 128 × 128 pixel CMOS image sensor with a column parallel analog-to-digital converter (ADC) circuit was fabricated using 0.35-mm CMOS technology. The resulting captured images are shown and the properties of improved pixel architecture are described. The image sensor has FPN of 1/28 that of the previous image sensor and an improved pixel architecture comprising a common in-pixel amp and a correlated double sampling (CDS) circuit. The use of a split photogate increases the sensitivity of the image sensor to 1.3 times that of the previous image sensor.     

Random noise filtering method based on the inter-frame registration

One of the problems to be solved in image processing is how to eliminate image noise effectively. In this work, we brought forward a random noise filtering method based on the inter-frame registration. Firstly, we calculated the relative displacement of the adjacent frames by a registration algorithm. Then we divided the image into the overlapping area and the non-overlapping area according to the relative displacement. Finally, we do noise reduction processing for these two areas respectively. The experiments results indicate that the proposed method can reduce noise in both spatial and time domain of video images. The main advantage is that it cannot only remove noise, but also effectively protect the image edge and detail information. Besides, it not only maintains the de-noising effect of traditional inter-frame algorithm, but also is suitable for moving targets. It has better real-time performance and wider application range.     

Principal component analysis of shear strain effects

Shear stresses are always present during quasi-static strain imaging, since tissue slippage occurs along the lateral and elevational directions during an axial deformation. Shear stress components along the axial deformation axes add to the axial deformation while perpendicular components introduce both lateral and elevational rigid motion and deformation artifacts into the estimated axial and lateral strain tensor images. A clear understanding of these artifacts introduced into the normal and shear strain tensor images with shear deformations is essential. In addition, signal processing techniques for improved depiction of the strain distribution is required. In this paper, we evaluate the impact of artifacts introduced due to lateral shear deformations on the normal strain tensors estimated by varying the lateral shear angle during an axial deformation. Shear strains are quantified using the lateral shear angle during the applied deformation. Simulation and experimental validation using uniformly elastic and single inclusion phantoms were performed. Variations in the elastographic signal-to-noise and contrast-to-noise ratios for axial deformations ranging from 0% to 5%, and for lateral deformations ranging from 0 to 5° were evaluated. Our results demonstrate that the first and second principal component strain images provide higher signal-to-noise ratios of 20 dB with simulations and 10 dB under experimental conditions and contrast-to-noise ratio levels that are at least 20 dB higher when compared to the axial and lateral strain tensor images, when only lateral shear deformations are applied. For small axial deformations, the lateral shear deformations significantly reduces strain image quality, however the first principal component provides about a 1–2 dB improvement over the axial strain tensor image. Lateral shear deformations also significantly increase the noise level in the axial and lateral strain tensor images with larger axial deformations. Improved elastographic signal and contrast-to-noise ratios in the first principal component strain image are always obtained for both simulation and experimental data when compared to the corresponding axial strain tensor images in the presence of both axial and lateral shear deformations.     

基于改进开关中值滤波的多孔网栅图像脉冲噪声消除

针对多孔网栅闪光照相图像含有随机脉冲噪声的问题,提出了一种改进的开关中值滤波噪声消除算法。该算法利用像素与邻域窗口统计中值的灰度信息,建立噪声点探测器。通过设置噪声点探测阈值来识别噪声,并用邻域窗口内统计中值代替噪声点取值。经过多次滤波,含随机脉冲噪声的计算机合成网栅图像及实验网栅图像可获得良好的恢复效果。     

Error estimation in measuring strain fields with DIC on planar sheet metal specimens with a non-perpendicular camera alignment

The determination of strain fields based on displacement components obtained via 2D-DIC is subject to several errors that originate from various sources. In this contribution, we study the impact of a non-perpendicular camera alignment to a planar sheet metal specimen's surface. The errors are estimated in a numerical experiment. To this purpose, deformed images - that were obtained by imposing finite element (FE) displacement fields on an undeformed image - are numerically rotated for various Euler angles. It is shown that a 3D-DIC stereo configuration induces a substantial compensation for the introduced image-plane displacement gradients. However, higher strain accuracy and precision are obtained - up to the level of a perfect perpendicular alignment - in a proposed “rectified” 2D-DIC setup. This compensating technique gains benefit from both 2D-DIC (single camera view, basic amount of correlation runs, no cross-camera matching nor triangulation) and 3D-DIC (oblique angle compensation). Our conclusions are validated in a real experiment on SS304.     

Elastic strain determination in semiconductor epitaxial layers by HREM

A new technique that is independent of image contrast and robust to the presence of experimental noise is presented to analyze strains from high resolution electron microscopy (HREM) lattice images. This approach involves the analysis of the cumulative sum of deviations (CUSUM) in lattice-fringe spacings from a target value. The effects of surface roughness at an interface, and surface relaxation due to transmission electron microscope (TEM) sample preparation are discussed. The CUSUM method was applied to two simulated and two experimental HREM images of semiconductor strained layer structures in [ ] zone axis projection. The CUSUM technique was able to accurately reproduce the strain profiles from the simulated and experimental images in all cases studied except for the component of the strain in the slip direction (e_xx) of an edge dislocation in a simulated image. In this case, the strain field near the core appeared hemispherical rather than lobed as expected.     

Automated fine grid technique for measurement of large-strain deformation maps

The fine grid technique has been a standard engineering tool for measuring large strains for many years. The sample surface is marked with a grid, and the deformation of this grid allows the deformation of the sample to be monitored. However, it has never been easy quantitatively to analyse the strain across the whole of a specimen's surface. We describe here an automated approach in which digitised images of a sample prepared with a grid are analysed by the Fourier transform method. This provides phase maps which, when unwrapped, yield planes representing the two in-plane specimen coordinates. An iterative technique follows these deforming planes from one frame to the next as the specimen deforms, allowing displacement fields to be calculated. Numerical differentiation gives strains across the specimen surface. Gerchberg iteration is used to provide immunity to errors resulting from holes or tears in the specimen surface. The method is demonstrated on a propellant simulant containing burn holes (a cylinder of diameter 10 mm; grid PITCH = 76 μm), loaded in compression across a diameter. All in-plane components of strain are calculated up to strains of approximately one-third. Displacement accuracy is of order 1 μm.     

Strain field denoising for digital image correlation using a regularized cost-function

In digital image correlation (DIC), the widely used forward-additive Newton–Raphson (FA-NR) algorithm and the recently introduced equivalent but more efficient inverse-compositional Gauss–Newton (IC-GN) algorithm are capable of providing both displacements and displacement gradients (strains) for each calculation point. However, the obtained displacement gradients are seriously corrupted by various noises, and for this reason these directly computed strains are usually considered as useless information and therefore discarded. To extract strain distributions more accurately, much research efforts have been dedicated to how to smooth and differentiate the noisy displacement fields using appropriate numerical approaches. In this contribution, contrary to these existing strain estimation approaches, a novel and alternative strain estimation approach, based on denoising the noisy strain fields obtained by FA-NR or IC-GN algorithm using a regularized cost-function, is proposed. The effectiveness and practicality of the proposed strain estimation technique is carefully examined using both computer-simulated images with imposed homogeneous and inhomogeneous deformation, and experimentally obtained images. Experimental results reveal that the strains obtained by the proposed method are comparable to those determined by post-processing of the displacement fields using conventional pointwise least squares strain estimation approach.     

基于能谱CT的材料组分彩色表征研究

基于光子计数探测器的X射线能谱CT,通过增加能谱分辨率实现了CT图像由灰度向彩色的转变,提高了材料识别能力。然而随着能谱通道数量的增加,通道中的噪声也显著增加,降低了材料识别的准确性。为充分利用能谱CT图像的稀疏性以及能谱通道之间图像的相关性,提出一种多约束窄谱CT迭代重建算法,可在降低噪声的同时有效保留图像的边缘及细节部分。进一步利用主成分分析对窄谱CT图像中的能谱信息进行估计,并建立主成分图像与R,G和B颜色分量之间的映射关系,最后获取彩色CT图像。该方法通过材料组分的彩色表征可以有效识别材料,同时降低图像中的背景噪声。仿真实验和实际实验结果验证了多约束窄谱CT迭代重建算法的有效性以及利用主成分分析进行材料组分彩色表征的可行性。     

The photonical, pure grid method

The paper presents an introduction on the pure grid method for deformation measurements in experimental mechanics. The pure grid method involves that the grid images are processed separately, and subsequently the results of these separate processings are substrated from each other in order to obtain a quantified deformation indication.The recording and processing of the grid images are currently performed photonically by means of digital image measurement systems. The basic data processing relations and set-ups of four different applicabilities of the photonical, pure grid method are presented in this paper. The applicabilities are discussed. Strains can be measured with errors smaller than 200 micro strain and displacements with errors smaller than of the diameter of the object as visible in the grid image. These figures can be improved substantially by future application of high resolving-power CCD cameras. Two examples are shown. The paper also contains an extensive bibliography for further explorations.     

Switching non-local vector median filter

This paper describes a novel image filtering method that removes random-valued impulse noise superimposed on a natural color image. In impulse noise removal, it is essential to employ a switching-type filtering method, as used in the well-known switching median filter, to preserve the detail of an original image with good quality. In color image filtering, it is generally preferable to deal with the red (R), green (G), and blue (B) components of each pixel of a color image as elements of a vectorized signal, as in the well-known vector median filter, rather than as component-wise signals to prevent a color shift after filtering. By taking these fundamentals into consideration, we propose a switching-type vector median filter with non-local processing that mainly consists of a noise detector and a noise removal filter. Concretely, we propose a noise detector that proactively detects noise-corrupted pixels by focusing attention on the isolation tendencies of pixels of interest not in an input image but in difference images between RGB components. Furthermore, as the noise removal filter, we propose an extended version of the non-local median filter, we proposed previously for grayscale image processing, named the non-local vector median filter, which is designed for color image processing. The proposed method realizes a superior balance between the preservation of detail and impulse noise removal by proactive noise detection and non-local switching vector median filtering, respectively. The effectiveness and validity of the proposed method are verified in a series of experiments using natural color images.