Automated analysis of brachial ultrasound image sequences: early detection of cardiovascular disease via surrogates of endothelial function

Early detection of cardiovascular disease would allow timely institution of preventive measures. Arterial endothelium play a primary role in processes leading to the development of atherosclerotic plaque and cardiovascular disease in general. Determination of flow-mediated dilatation (FMD) of brachial arteries from B-mode ultrasound image sequences offers a noninvasive surrogate index of endothelial function. A highly automated method for analysis of brachial ultrasound image sequences is reported and its performance assessed. The method overcomes the variability of brachial ultrasound images across subjects by incorporating machine learning and quality control steps. The automated method outperformed conventional manual analysis by providing a decreased analysis bias, increased reproducibility, and improved measurement accuracy. Consequently, it decreases inter- and intraobserver as well interinstitution variability. The method has been employed in a number of population studies with thousands of subjects analyzed.     

A system for real-time measurement of the brachial artery diameter in B-mode ultrasound images.

The measurement of the brachial artery diameter is frequently used in clinical studies for evaluating the flow-mediated dilation and, in conjunction with the blood pressure value, for assessing arterial stiffness. This paper presents a system for computing the brachial artery diameter in real-time by analyzing B-mode ultrasound images. The method is based on a robust edge detection algorithm which is used to automatically locate the two walls of the vessel. The measure of the diameter is obtained with subpixel precision and with a temporal resolution of 25 samples/s, so that the small dilations induced by the cardiac cycle can also be retrieved. The algorithm is implemented on a standalone video processing board which acquires the analog video signal from the ultrasound equipment. Results are shown in real-time on a graphical user interface. The system was tested both on synthetic ultrasound images and in clinical studies of flow-mediated dilation. Accuracy, robustness, and intra/inter observer variability of the method were evaluated.     

Statistical approach to quantify the presence of phase coupling using the bispectrum

The bispectrum is a method to detect the presence of phase coupling between different components in a signal. The traditional way to quantify phase coupling is by means of the bicoherence index, which is essentially a normalized bispectrum. The major drawback of the bicoherence index (BCI) is that determination of significant phase coupling becomes compromised with noise and low coupling strength. To overcome this limitation, a statistical approach that combines the bispectrum with a surrogate data method to determine the statistical significance of the phase coupling is introduced. Our method does not rely on the use of the BCI, where the normalization procedure of the BCI is the major culprit in its poor specificity. We demonstrate the accuracy of the proposed approach using simulation examples that are designed to test its robustness against noise contamination as well as varying levels of phase coupling. Our results show that the proposed approach outperforms the bicoherence index in both sensitivity and specificity and provides an unbiased and statistical approach to determining the presence of quadratic phase coupling. Application of this new method to renal hemodynamic data was applied to renal stop flow pressure data obtained from normotensive (N = 7) and hypertensive (N = 7) rats. We found significant nonlinear interactions in both strains of rats with a greater magnitude of coupling and smaller number of interaction peaks in normotensive rats than hypertensive rats.     

A fuzzy approach to deal with uncertainty in image forensics

Image forensics research has mainly focused on the detection of artifacts introduced by a single processing tool, thus resulting in the development of a large number of specialized algorithms looking for one or more specific footprints under precise settings. As one may guess, the performance of such algorithms are not ideal, so the output they provide may be noisy, inaccurate and only partially true. Moreover, in real scenarios a manipulated image is often the result of the application of several tools made available by the image processing software. As a consequence, reliable tamper detection requires that several tools developed to deal with different scenarios are applied. The above observations raise two new problems: (i) deal with the uncertainty introduced by error-prone tools and (ii) devise a sound strategy to merge the information provided by the different tools into a single output. To overcome these problems we propose a decision fusion framework based on the Fuzzy Theory, which permits to cope with the uncertainty and lack of precise information typical of image forensics, by leveraging on the widely known ability of the Fuzzy Theory to deal with inaccurate and incomplete information. We describe a practical implementation of the proposed framework and validate it in a realistic scenario in which five forensic tools exploit JPEG compression artifacts to detect cut&paste tampering within a specified region of an image. The results are encouraging, and provide a significant advantage with respect to those obtained by simply OR-ing the outputs of the single tools.     

一种修复细化指纹图像中断裂线条的新方法

提出了一种新的针对细化指纹图像的修复方法，通过参照附近有效指纹线条的走向来还原或者修复断裂了的指纹线条，突破了只有近距离近似方向才能修复的局限，修补了本该连接的断裂指纹线条，有利于提高指纹特征值提取的精确性。实验结果表明，不管两断裂点距离是近还是远，两断裂点所在指纹线条的方向相差多大，这种方法均能够很好地修复指纹图像。     

深度学习算法在颈动脉超声图像斑块分割中的应用研究

近年来,随着计算机技术的进步和数据集的大规模化,越来越多的人把计算机视觉技术应用到超声医学图像中.但在超声图像方面却存在低准确度且不稳定产生的模糊、伪影等使现有算法对模糊、噪声图像误判较高.另外由于病例过多,人为的去检测和识别斑块过于繁琐.为了缓解这些问题,提出了采用inception的网络结构方法快速准确地获取高噪声...     

A novel approach to the 2-D blind deconvolution problem in medical ultrasound

The finite frequency bandwidth of ultrasound transducers and the nonnegligible width of transmitted acoustic beams are the most significant factors that limit the resolution of medical ultrasound imaging. Consequently, in order to recover diagnostically important image details, obscured due to the resolution limitations, an image restoration procedure should be applied. The present study addresses the problem of ultrasound image restoration by means of the blind-deconvolution techniques. Given an acquired ultrasound image, algorithms of this kind perform either concurrent or successive estimation of the point-spread function (PSF) of the imaging system and the original image. In this paper, a blind-deconvolution algorithm is proposed, in which the PSF is recovered as a preliminary stage of the restoration problem. As the accuracy of this estimation affects all the following stages of the image restoration, it is considered as the most fundamental and important problem. The contribution of the present study is twofold. First, it introduces a novel approach to the problem of estimating the PSF, which is based on a generalization of several fundamental concepts of the homomorphic deconvolution. It is shown that a useful estimate of the spectrum of the PSF can be obtained by applying a proper smoothing operator to both log-magnitude and phase of the spectra of acquired radio-frequency (RF) images. It is demonstrated that the proposed approach performs considerably better than the existing homomorphic (cepstrum-based) deconvolution methods. Second, the study shows that given a reliable estimate of the PSF, it is possible to deconvolve it out of the RF-image and obtain an estimate of the true tissue reflectivity function, which is relatively independent of the properties of the imaging system. The deconvolution was performed using the maximum a-posteriori (MAP) estimation framework for a number of statistical priors assumed for the reflectivity function. It is shown in a series of in vivo experiments that reconstructions based on the priors, which tend to emphasize the "sparseness" of the tissue structure, result in solutions of higher resolution and contrast.     

A combinatorial approach to probabilistic results on the linear-complexity profile of random sequences

The linear-complexity profile measures the extent to which the initial segments of a keystream sequence can be simulated by linear feedback shift-register sequences. To provide a benchmark for the assessment of keystream sequences, a probabilistic theory of the linear-complexity profile of random sequences is needed. For sequences of elements of a finite field we show probabilistic results that can be derived by a combinatorial method.     

A Robust hierarchical motion estimation algorithm in noisy image sequences in the bispectrum domain

The present study describes a robust hierarchical motion estimation algorithm in noisy image sequences using the bispectrum. The motion can be characterized by an affine model and the parameters of an affine motion model are estimated by means third-order auto-bispectrum and cross-bispectrum measures. The basic components of this framework to obtain motion vectors are (i) pyramid construction, (ii) motion estimation and (iii) coarse-to-fine refinement. The entire motion is decomposed as a global and a local motion field, which helps accurately obtain high resolution estimates for the local motion field. Simulation results are presented and compared to those obtained from the phase correlation algorithm. The results demonstrate that the proposed method is more suited than the phase correlation algorithm to analyses complex noisy image sequences. On the other hand, our method produces smoother displacement vector field with a more accurate measure of object motion in different signal-to-noise ratio scenarios.     

一种对亮度变化鲁棒的相关跟踪方法

针对复杂背景目标跟踪过程中,目标亮度和对比度发生变化易导致跟踪不稳定或失败的问题,提出了一种对亮度变化鲁棒的相关跟踪方法。该方法利用图像相位一致性特征对亮度变化不敏感的特点,对原始图像进行相位一致性计算,得到相位一致性图像,再采用传统的最小绝对差(MAD)相关跟踪方法对目标进行跟踪。实验结果表明,该方法对图像的亮度变化具有很强的适应性,较好地解决了传统相关跟踪算法因图像亮度变化导致跟踪点漂移甚至目标丢失的问题。     

A model to quantify reliability of human performance in man-machine systems

To quantify reliability of human performance in a man-machine system a Markovian model for estimating the number of cycles that a worker performs without committing and error has been presented. Methods of collecting data, subsequent analysis, and various types of errors made by workers have been described. For illustrating the application of the model, results of an experimental study have been used.     

A new approach to reduce the `blocking effect' of transform coding[image coding]

A combined-transform coding (CTC) scheme to reduce the blocking effect of conventional block transform coding and hence to improve the subjective performance is presented. The scheme is described, and its information-theoretic properties are discussed. Computer simulation results for a chest X-ray image are presented. The CTC scheme, the JPEG baseline scheme, and the conventional discrete Walsh-Hadamard transform (DWHT) are compared to demonstrate the performance improvement for the CTC scheme. The advantages of the CTC scheme include no ringing effect as there is no error propagation across the boundary, no additional computation, and distortion always held within a certain level     

数字全变分滤波在红外图像序列非均匀校正中的应用

红外焦平面阵列上的空间非均匀性,即固定图案噪声,严重影响了红外系统的成像质量。为此提出了一种新的非均匀校正算法,它借鉴了图像处理中的图像去噪思想,把数字全变分滤波器引入非均匀校正。鉴于数字全变分滤波的执行过程一般都是自我迭代,而考虑到校正算法的实时性要求,无法对单帧图像实施多次处理。故而将以前的空间迭代形式转化为时间递推,以达到逐帧去除固定图案噪声的目的。使用仿真和真实红外图像序列对算法性能进行验证,实验结果表明:该算法从第15帧开始就能够达到较好的校正水平,并且在未优化条件下,每秒钟处理30帧图像仅需300M个指令周期。因此具有收敛速度快、计算复杂度低等优点。     

A model to quantify the effects of sensitivity time control onradar-to-radar interference

This paper develops a method to calculate the effects of sensitivity time control (STC) on interference, experienced by one radar, caused by another radar. The probability density function (PDF) of STC attenuation is determined by, and is related to the overall probability distribution that determines the probability of interference. This method is consistent with, and complementary to the method of calculating the effects of antenna-to-antenna coupling between the radars     

A new approach to evaluation of hot-carrier lifetime of ringoscillator (RO)

The paper presents a novel experimental method to evaluate AC hot-carrier lifetime of a ring oscillator (RO). By using a series of different stages of ring oscillators (DSROs), the new method allows one to maintain a constant frequency (f₀) and obtain a closer value between pulse-to-pulse voltage (V_p-p) and bias condition throughout the RO lifetime testing. These two achievements eliminate the innate flaws in conventional RO hot-carrier test method. Hence, a more reliable AC lifetime of RO is expected     

A new technique to quantify deuterium passivation of interfacetraps in MOS devices

The ubiquitous presence of hydrogen in the fabrication of complementary metal oxide semiconductor (CMOS) devices results in the passivation of most interface traps by hydrogen. In this letter, we show that this hydrogen cannot be completely replaced by deuterium through a one-step deuterium anneal process. Improved device reliability attributed to deuterium incorporation at the oxide/silicon interface is thus limited by the remnant hydrogen. To determine the deuterium passivation fraction, we propose a new technique that is based solely on electrical testing. Compared to other techniques such as secondary ion mass spectrum (SIMS), the new technique can be used to measure the deuterium passivation fraction in deep submicron MOS devices with very small testing areas     

多层系统周期样品PSTM消假像微扰近似

本文利用一级微扰近似方法对三层系统（样品台－样品－空气）表面周期起伏样品采用π－对称双激光束照射得到等强度和等高度扫描的数值模拟近场强度图像。通过与单激光束照射图像比较,作者看到双激光束照射下的一级微扰图像能够除去由样品表面起伏的微扰而产生的动量局域偏移,也可减少由表面倾角引起的假像。此三层系统起伏样品能够较真实地模拟实验,对PSTM的实际探测有一定的指导意义。