Tissue velocity imaging of coronary artery by rotating-type intravascular ultrasound

Intravascular ultrasound (IVUS) provides not only the dimensions of coronary artery but the information of tissue components. In catheterization laboratory, soft and hard plaques are classified by visual inspection of echo intensity. So-called soft plaque contains lipid core or thrombus and it is believed to be more vulnerable than a hard plaque. However, it is not simple to analyze the echo signals quantitatively. When we look at a reflection signal, the intensity is affected by the distance of the object, the medium between transducer and objects and the fluctuation caused by rotation of IVUS probe. The time of flight is also affected by the sound speed of the medium and Doppler shift caused by tissue motion but usually those can be neglected. Thus, the analysis of RF signal in time domain can be more quantitative than intensity of RF signal. In the present study, a novel imaging technique called "intravascular tissue velocity imaging" was developed for searching a vulnerable plaque. Radio-frequency (RF) signal from a clinically used IVUS apparatus was digitized at 500 MSa/s and stored in a workstation. First, non-uniform rotation was corrected by maximizing the correlation coefficient of circumferential RF signal distribution in two consecutive frames. Then, the correlation and displacement were calculated by analyzing the radial difference of RF signal. Tissue velocity was determined by the displacement and the frame rate. The correlation image of normal and atherosclerotic coronary arteries clearly showed the internal and external borders of arterial wall. Soft plaque with low echo area in the intima showed high velocity while the calcified lesion showed the very low tissue velocity. This technique provides important information on tissue character of coronary artery.     

Acoustic properties of aortic aneurysm obtained with scanning acoustic microscopy

In aortic aneurysm tissues, macrophages and their secretion of matrix metalloproteinases (MMPs) are playing important role for tissue degeneration. Some studies have shown that weakening of the mechanical properties of the degenerated tissues may progress the expansion of the aneurysm. However, actual measurement of the mechanical properties has not been investigated at microscopic level. The objective of the present study is to assess the mechanical properties of aortic aneurysm tissues by measuring acoustic properties by scanning acoustic microscopy (SAM). Twenty-one cases of aortic aneurysm including renal and common iliac aneurysm tissues were surgically excised. Each tissue was fixed by 4% formaldehyde and the specimens were treated as (1) picrosirius red staining for normal and polarized light microscopy, (2) CD68 staining for macrophage detection, and (3) no staining for acoustic microscopy. A specially developed SAM system operating in the frequency range of 100-200 MHz, was employed in the measurement. Images of amplitude and phase are obtained in a field of 2x2 mm. The intima was mainly consisted of degenerated collagen without polarization of picrosirius red staining. Macrophages stained by CD68 were observed near the degenerated collagen fibers. The sound speed was 1567 m/s in the intima, 1576 m/s in the media, 1640 m/s in the adventitia, respectively. Infiltration of macrophages showed higher values of attenuation and sound speed than the surrounding tissues. The sound speed of the intima was significantly lower than our previous measurement of atherosclerotic aorta without aneurismal change. As the tissue elasticity is closely correlated with the sound speed, the elasticity of the intima was considered to be lower in aneurysm tissues. This mechanical weakness may contribute to the expansion of the diameter of the aneurysm. Acoustic microscopy provided important data for assessing tissue mechanical properties of abdominal aneurysm.     

Processing a sequence of images for super-resolution problem solving

An algorithm is proposed that is capable of processing a sequence of images so as to increase their resolution and overcome restrictions imposed by a finite number of sensitive elements in the radiation detector. The image size is increased using a spectral interpolation method. A method of selecting reference frames and determining interframe displacement vectors is described. Results of application of the proposed algorithm to real images are presented.     

立体摄影术与数字散斑相关方法相结合用于研究三维变形场

采用立体摄影术与数字图像相关技术相结合的方法测量了三维位移场。首先利用两个CCD摄像机在空间两个不同位置拍摄物体表面在变形前后同一个区域之间的散斑图像;然后利用数字散斑相关技术求解这四幅散斑图像之间的相对位移;最后利用立体摄影的几何转换公式来确定物体表面的三维变形场。给出了该立体摄影测试系统的标定结果以及编织复合材料试件的三维变形测量结果。     

基于光学相关器的光学稳像器研究

为了突破传统电子稳像和机械稳像技术在处理速度、精度等方面的局限性,提出基于光学相关器的稳像技术,旨在实现对高速视频的实时高精度光学稳像。系统使用光学联合相关变换的方法,提取视频前后两帧变换后的相关峰,给出两帧的位移差值,通过改进后的补偿算法进行实时稳像。基于光学相关器的光学稳像器能够实现平移和旋转稳像,通过仿真和实验分析,平移稳像的精度可以达到0.1个像元（改进补偿算法后可达0.04个像元）,旋转稳像的精度可达0.1。     

Experimental study on the micromechanical behavior of a PBX simulant using SEM and digital image correlation method

The micro-scale mechanical behavior of a polymer-bonded explosive (PBX) simulant was experimentally studied using a scanning electron microscope (SEM) imaging system and digital image correlation (DIC) method. The semi-circular bend (SCB) test was chosen for the study. During the testing, a series of SEM images of the specimen was acquired in situ. The natural micro-structural features of the specimen were used as random speckle pattern for DIC analysis. The displacement and strain fields at the area of interest were obtained by DIC. The deformation and damage of PBX were analyzed. Heterogeneous strain fields demonstrated the damage evolution underneath the specimen surface and predicted possible micro-crack growth. Based on the contour plots of the correlation coefficient, the formation and extension of microscopic cracks were quantitatively analyzed.     

An improved image alignment procedure for high-resolution transmission electron microscopy

Image alignment is essential for image processing methods such as through-focus exit-wavefunction reconstruction and image averaging in high-resolution transmission electron microscopy. Relative image displacements exist in any experimentally recorded image series due to the specimen drifts and image shifts, hence image alignment for correcting the image displacements has to be done prior to any further image processing. The image displacement between two successive images is determined by the correlation function of the two relatively shifted images. Here it is shown that more accurate image alignment can be achieved by using an appropriate aperture to filter the high-frequency components of the images being aligned, especially for a crystalline specimen with little non-periodic information. For the image series of crystalline specimens with little amorphous, the radius of the filter aperture should be as small as possible, so long as it covers the innermost lattice reflections. Testing with an experimental through-focus series of Si[1 1 0] images, the accuracies of image alignment with different correlation functions are compared with respect to the error functions in through-focus exit-wavefunction reconstruction based on the maximum-likelihood method. Testing with image averaging over noisy experimental images from graphene and carbon-nanotube samples, clear and sharp crystal lattice fringes are recovered after applying optimal image alignment.     

Application of stereo vision to the study of mixed-mode crack-tip deformations

A stereo vision is applied to evaluate crack-tip parameters for fracture specimens subjected to a mixed-mode loading (tension and shear). By using a special loading device, the applied remote loading is oriented at an angle with respect to the axis of the crack. At each loading angle, the calibrated vision system was rotated so that the axis of the crack is parallel to the horizontal or vertical axis of the image frame. At a load close to the crack initiation, the displacement field around the crack-tip region of the fracture specimen was measured relative to a specimen coordinate system located at the crack tip of the fracture specimen. During the experiment, the fracture specimen was subjected to rigid body translation and rotation. Hence, the displacement fields are affected by the rigid body translation and rotation. Using the experimentally determined displacements and the analytically determined displacements with several higher order terms being included, the stress intensity factors and the amount of rigid body translation and rotation were calculated through a least-squares fit. The effect of the rigid body motion on the measured displacements was then eliminated using the computed rigid body translation and rotation. Experimental results indicate that a K_I and K_II dominant region is observed in the corrected displacement fields.     

Two-frame phase-shifting interferometry for retrieval of smooth surface and its displacements

A new two-frame interferometric method with a blind phase shift of a reference wave is proposed for the reconstruction of smooth surface relief areas. In this method, a correlation approach based on the determination of correlation coefficient between intensity distributions of two interferograms is applied for the phase shift extraction. An algorithm for this method realization is developed and its performance is verified on test surfaces. An experimental setup containing a Twiman-Green interferometer was used in the reconstruction of smooth surfaces of metal specimens using the developed algorithm. Surface displacement phase fields were generated in case of a CT-notched specimen made of an aluminum alloy by the interactive procedure of element stitching of two surface reliefs and subtracting the surface relief after cyclic loading from the initial one. The received surface displacement fields allow us to determine the studied specimen fatigue process zone (FPZ) and FPZ size.     

A simple-shear rheometer for linear viscoelastic characterization of vocal fold tissues at phonatory frequencies

Previous studies reporting the linear viscoelastic shear properties of the human vocal fold cover or mucosa have been based on torsional rheometry, with measurements limited to low audio frequencies, up to around 80 Hz. This paper describes the design and validation of a custom-built, controlled-strain, linear, simple-shear rheometer system capable of direct empirical measurements of viscoelastic shear properties at phonatory frequencies. A tissue specimen was subjected to simple shear between two parallel, rigid acrylic plates, with a linear motor creating a translational sinusoidal displacement of the specimen via the upper plate, and the lower plate transmitting the harmonic shear force resulting from the viscoelastic response of the specimen. The displacement of the specimen was measured by a linear variable differential transformer whereas the shear force was detected by a piezoelectric transducer. The frequency response characteristics of these system components were assessed by vibration experiments with accelerometers. Measurements of the viscoelastic shear moduli (G' and G") of a standard ANSI S2.21 polyurethane material and those of human vocal fold cover specimens were made, along with estimation of the system signal and noise levels. Preliminary results showed that the rheometer can provide valid and reliable rheometric data of vocal fold lamina propria specimens at frequencies of up to around 250 Hz, well into the phonatory range.     

Super-resolution PIV by recursive local-correlation

This paper presents a method of accurately determining the displacement of tracer particles between two images using recursive correlation. The local correlation value is iteratively arrived at through successive approximations of local displacement using increasingly smaller regions of determination. By starting with a large search area and iteratively narrowing the search restricting the search after each iteration based on the resulting calculation, very high-resolution PIV processing can be achieved. Spurious vectors are eliminated and accuracy and processing speed is maintained by correlating images in compressed (sparse array) format using second-order spatial correlation. The methodology of this unique image analysis method is presented along with a discussion of its limitations and applicability.     

In vitro ultrasonic characterization of human cancellous femoral bone using transmission and backscatter measurements: relationships to bone mineral density

Thirty-eight slices of pure trabecular bone 1-cm thickness were extracted from human proximal femurs. A pair of 1-MHz central frequency transducers was used to measure quantitative ultrasound (QUS) parameters in transmission [normalized broadband ultrasound attenuation (nBUA), speed of sound (SOS)] and in backscatter [broadband ultrasound backscatter (BUB)]. Bone mineral density (BMD) was measured using clinical x-ray quantitative computed tomography. Site-matched identical region of interest (ROIs) of 7 x 7 mm2 were positioned on QUS and QCT images. This procedure resulted in 605 ROIs for all the specimens data pooled together. The short-term precision of the technique expressed in terms of CV was found to be 2.3% for nBUA, 0.3% for SOS and 4.5% for BUB. Significant linear correlation between QUS and BMD were found for all the 605 ROIs pooled, with r2 values of 0.73, 0.77, and 0.58 for nBUA, SOS, and BUB, respectively (all p < 0.05). For the BUB, the best regression was obtained with a polynomial fit of second order (r2 = 0.63). An analysis of measurements errors was developed. It showed that the residual variability of SOS is almost completely predicted by measurements errors, which is not the case for BUA and BUB, suggesting a role for micro-architecture in the determination of BUA and BUB.     

Effect of temperature increase and freezing on intravascular elastography

Intravascular ultrasound (IVUS) elastography is a technique that assesses the local strain in the vessel wall and plaque. The strain is an important parameter for characterization of different plaque components. These regions are related to plaque vulnerability. IVUS elastography was validated in vitro using human coronary and femoral arteries. These experiments were performed on specimens that were stored frozen and measured at room temperature for practical issues. The aim of this study is to determine the influence of freezing and measuring the tissues at room temperature (23 degrees C instead of 37 degrees C) on the elastic properties. Four human coronary, one carotid and one femoral arteries were first measured at 23 degrees C and next at 37 degrees C. Additionally they were stored at -80 degrees C for up to 24 h and finally measured at 23 degrees C. Acquisitions at intraluminal pressures of 80 and 100 mmHg were performed using an EndoSonics 20 MHz Visions catheter. Elastograms were determined from the IVUS rf-data (sampled at 100 MHz in 12 bits) that were obtained from a digital interface. Qualitative and quantitative analysis of the elastograms obtained from fresh and frozen specimens measured at 23 degrees C reveals that storage of the specimen at -80 degrees C has no significant influence. In vitro experiments can be performed at room temperature after storage of the tissue at -80 degrees C without significant affection of the information with respect to measuring fresh ex vivo material at body temperature.     

基于联合变换相关的机载航空相机像移测量

为了提高像移测量精度,针对机载航空摆扫相机提出一种坐标变换法和图像相关法相结合的像移测量方法。利用坐标变换法得到初始像移速度,利用图像联合变换相关法对像移速度残差进行补偿。联合图像通过一个面阵CCD获得,该面阵CCD放置在相机焦平面上并与成像线阵TDI CCD平行,其输出的当前图像与参考图像合并构成联合图像进行二维空间联合变换相关运算,得到像移修正矢量。对该矢量分别在相机摆扫方向和载机飞行方向进行分解,从而得到摆扫像移和前向像移的修正量。仿真实验结果表明,在输入图像信噪比为4 dB时,像移测量误差在0.1 pixel以内。     

A Highly Accurate Face Recognition System Using Filtering Correlation

The authors previously constructed a highly accurate fast face recognition optical correlator (FARCO) [E. Watanabe and K. Kodate: Opt. Rev. 12 (2005) 460], and subsequently developed an improved, super high-speed FARCO (S-FARCO), which is able to process several hundred thousand frames per second. The principal advantage of our new system is its wide applicability to any correlation scheme. Three different configurations were proposed, each depending on correlation speed. This paper describes and evaluates a software correlation filter. The face recognition function proved highly accurate, seeing that a low-resolution facial image size (64 × 64 pixels) has been successfully implemented. An operation speed of less than 10 ms was achieved using a personal computer with a central processing unit (CPU) of 3 GHz and 2 GB memory. When we applied the software correlation filter to a high-security cellular phone face recognition system, experiments on 30 female students over a period of three months yielded low error rates: 0% false acceptance rate and 2% false rejection rate. Therefore, the filtering correlation works effectively when applied to low resolution images such as web-based images or faces captured by a monitoring camera.     

In vivo three-dimensional spectral domain endoscopic optical coherence tomography using a microelectromechanical system mirror

A biopsy is a well-known medical test used to evaluate tissue abnormality. Biopsy specimens are invasively taken from part of a lesion and visualized by microscope after chemical treatment. However, diagnosis by means of biopsy is not only variable due to depth and location of specimen but may also damage the specimen. In addition, only a limited number of specimens can be obtained, thus, the entire tissue morphology cannot be observed. We introduce a three-dimensional (3-D) endoscopic optical biopsy via optical coherence tomography employing a dual-axis microelectromechanical system scanning mirror. Since this technique provides high-resolution, noninvasive, direct, and multiple visualization of tissue, it could function as a clinical biopsy with advanced performance. The device was integrated with a conventional endoscope and utilized to generate in vivo 3-D clinical images in humans and animals.     

Heterogeneous in vivo MR images of soft tissue tumors: guide to gross specimen sampling.

Twelve soft tissue tumors preoperatively studied with magnetic resonance (MR) imaging contained areas of inhomogeneous intralesional signal intensity. The pathologist's selection of biopsy sites from gross specimens was based on specific MR images selected by a radiologist and depended on close cooperation between the radiologist and pathologist. The histopathology so sampled, further depended on the lesion's size, careful gross specimen orientation, discrete sampling, and a specially developed Grid Analysis technique. Our initial experience indicates that (1) histology may vary within different and often neighboring sites of a single soft tissue lesion; (2) that such variability is common in soft tissue tumors; (3) that histological variability within different sites of a single lesion influences signal heterogeneity; and (4) that although differing MR signal intensities per se are not tissue specific, MR may enhance the histopathological accuracy of pathologists who can be directed to particular gross specimen sites by magnetic resonance images. To our knowledge such a specific, detailed effort has not been made.     

Improved sensitivity of MRI in multiple sclerosis by use of extensive standardized procedures

The relative value of two different MRI procedures for the assessment of infratentorial extension in multiple sclerosis (MS) was studied. Multislice spin-echo techniques were used overall. Procedure A consisted of parasagittal T1-weighted images (500/30) and axial T2-weighted images (2500/30, 2500/120). Procedure B consisted of parasagittal T2-weighted images (1600/35, 1600/90). In the parasagittal T2-weighted images clear visualization of MS lesions is achieved because signal intensities of CSF and normal nervous tissue are nearly identical. All images were performed with a 0.5 Tesla MR system. Data were obtained in 98 patients with definite (N = 30) or probable MS (N = 68). Areas with abnormal signal intensity in the infratentorial regions (brainstem, cerebellum, and/or cervical spinal cord) were identified in 44% of the patients with procedure A and in 64% with procedure B. The standard application of the combination of both procedures improves the sensitivity of the MR examination for the diagnosis of MS, the delineation of infratentorial lesions and the correlation between clinical and MR data without excessively increasing imaging time.     

A linear least squares approach for evaluation of crack tip stress field parameters using DIC

In the present work, an experimental study is carried out to estimate the mixed-mode stress intensity factors (SIF) for different cracked specimen configurations using digital image correlation (DIC) technique. For the estimation of mixed-mode SIF׳s using DIC, a new algorithm is proposed for the extraction of crack tip location and coefficients in the multi-parameter displacement field equations. From those estimated coefficients, SIF could be extracted. The required displacement data surrounding the crack tip has been obtained using 2D-DIC technique. An open source 2D DIC software Ncorr is used for the displacement field extraction. The presented methodology has been used to extract mixed-mode SIF׳s for specimen configurations like single edge notch (SEN) specimen and centre slant crack (CSC) specimens made out of Al 2014-T6 alloy. The experimental results have been compared with the analytical values and they are found to be in good agreement, thereby confirming the accuracy of the algorithm being proposed.     

用数字图像相关技术预测土壤开裂

介绍使用数字图像相关技术预测土壤开裂的方法。通过对定时得到的一组数字图像进行相关运算得到一组二维位移场，位移的矢量表示展现在计算机屏幕上就成功地展示了开裂裂纹的形态。预测的开裂趋势与实际发生的是一致的。