基于肝脏超声图像的纤维化量化分析

超声诊断除了受主观性和诊断经验等人为因素影响外,检测频率、机器参数的设置等成像条件的变化也会对图像产生很大的影响,因而使肝脏纤维化的量化分析受到很大限制.本文基于任意的肝脏超声图像提出了利用纹理边缘共生矩阵(TECM)进行纤维化量化分析的方法,首先由Canny算子提取纹理边缘,并计算其共生矩阵的熵作为分类的特征值.通过用leave-one-out最近邻法和Fisher线性分类器进行分类试验,证明其分类精度优于分形维(FD).而且,用Fisher线性分类器对TECM和差分盒计数法(DBC)组成的联合特征向量(J-DT)进行分类试验,当阈值为时,分类正确率(CCR)可以达到95.1%;取阈值为时,灵敏性可以达到100%.     

超薄覆层低频超声类瑞利波定征方法

本文提出低频超声类瑞利波定征方法来估计覆层／基层层状复合结构超薄覆层的纵波声速,横波声速,厚度和密度等参数。这里“超薄”的概念是指覆层厚度ｈ远小于覆层中的声波波长λ,导致在时域上覆层前后界面的各次回波信号相互混迭。文章采用水楔耦合方式,利用超声漏类瑞利波频域分析方法获取层状复合结构超声类瑞利波色散曲线,提出以色散特性为基础的低频超声类瑞利波覆层定征方法和在最小二乘意义下以色散曲线为基础的反向算法对     

超薄覆层低频超声类瑞利波定征方法

本文提出低频超声类瑞利波定征方法来估计覆层/基层层状复合结构超薄覆层的纵波声速、横波声速、厚度和密度等参数。这里“超薄”的概念是指覆层厚度h远小于覆层中的声波波长λ,导致在时域上覆层前后界面的各次回波信号相互混迭。文章采用水楔耦合方式,利用超声漏类瑞利波频域分析方法获取层状复合结构超声类瑞利波色散曲线,提出以色散特性为基础的低频超声类瑞利波覆层定征方法和在最小二乘意义下以色散曲线为基础的反向算法对覆层进行了参数估计。文中分析了影响估计准确性的各种因素,研究了低频超声类瑞利波定征方法对覆层各参数的灵敏度及其在误差传递中的意义。实验结果证实,对于银箔/玻璃层状复合结构,该方法能够准确估计厚度小到26μm银箔覆层的声学参数。     

超薄单向纤维增强复合材料低频多模式超声兰姆波定征方法

提出低频多模式超声兰姆波定征方法来估计超薄层状单向纤维增强复合材料的密度、厚度、弹性常数等参数。这里"超薄"的概念是指材料厚度h远小于材料中的声波波长λ,导致在时域上材料前后界面的各次回波信号相互混迭。分析了沿平行和垂直于纤维两个方向上,在超薄层状单向纤维增强复合材料中传播的低频兰姆波色散特性,提出在最小二乘意义下以材料色散曲线为基础的反向算法对材料参数进行了估计。文中分析了影响估计准确性的各种因素,研究了该方法对材料参数的灵敏度及其在误差传递中的意义。结合超声漏兰姆波频域分析方法,并使用超声耦合剂耦合方式和一对中心频率为2MHz的宽带纵波换能器,实验结果证实,该方法能够准确估计h<0.05 λ的单向玻璃纤维增强双酚A型聚砜(PSF)复合材料的材料参数。      

图像纹理分析在彩色印刷品质量检测中的应用研究

图像处理技术为彩色印刷品的缺陷检测提供了一种新的途径.将图像的纹理分析应用于缺陷检测过程,比较标准图像和待检图像的纹理特征参数就可以分析待检图像细微层次方面的质量,从而检测出印刷缺陷.实验表明,这种缺陷检测方法精度和效率高,满足精细彩色印刷品的要求.     

血管内超声图像后处理综述

血管内超声显像是目前临床常用的诊断血管病变的介入影像手段,可在活体中观察血管壁和管腔的形态,以及斑块的形态和成分。采用数字图像处理技术,对血管内超声图像序列进行自动或半自动地处理和分析,对于血管病变的计算机辅助诊断和制定最佳诊疗方案具有重要意义。本文就近年来血管内超声图像计算机后处理的研究现状进行综述,包括图像分割和组织标定、运动伪影的抑制、血管的三维重建、血管形态和血流动力学参数的测量、组织定征显像及与其他影像的融合等,评价了目前的研究情况,并对未来的研究提出了展望。     

超声背散射信息熵成像评价脂肪肝的新方法

提出超声背散射Tsallis信息熵成像评价脂肪肝的新方法。利用滑动窗口法,估算窗口内局部背散射包络信号的Tsallis信息熵参数值,对信息熵参数值矩阵进行扫描变换、颜色映射及感兴趣区域设置,叠加到超声B模式图像,实现Tsallis信息熵成像。分析72名肝脏捐献者和204名患者的超声背散射信号,参考标准分别为磁共振波谱测得的肝脏脂肪分数(Hepatic Fat Fraction, HFF)和肝活检组织学检查测得的脂肪肝程度。对于72名肝脏捐献者,Tsallis信息熵与lg(HFF)的相关系数r=0.67(P<0.000 1)。对于204名患者,受试者工作特征曲线下面积分别为0.82、0.88、0.89(≥轻度、≥中度、≥重度),而超声背散射零差K成像分别为0.76、0.82、0.82。超声背散射Tsallis信息熵成像可以直观定征并定量评价脂肪肝的严重程度,其诊断性能优于超声背散射零差K成像,可作为一种超声评价脂肪肝的新方法。     

应用ICA滤波器技术提取图像纹理特征

针对纹理图像分类问题,本文提出了一种应用ICA滤波器技术提取图像纹理特征的方法.该方法首先从训练图像集中随机抽取图像块作为观测信号,应用ICA技术,提取滤波器组.然后根据训练样本图像对滤波器组的响应值来评估和选择滤波器组,达到降维的目的.最后利用滤波器组对测试图像进行滤波,得到该图像的滤波响应结果,从该响应结果中得到最大响应滤波器编号,提取其直方图作为图像的全局特征和局部特征.对Brodatz纹理图像集中108个纹理类别进行了分类实验,结果表明,与MPEG-7纹理描述子相比,该图像特征对纹理图像具有更好的分类效果.     

超声在电弧焊接中的应用

超声场作为一种高效清洁的物理场在电弧焊接中具有越来越多的应用。在电弧焊接过程中,引入超声,可以有效改善电弧形态、熔滴过渡以及焊缝组织,最终提高焊接接头力学性能。超声在电弧焊接过程中的应用特点主要与超声施加方法有关,不同的超声施加方法具有不同的特点,根据不同的超声施加方法可将超声电弧复合焊接分为不同类型。主要综述了电弧超声技术、超声与电弧同轴复合、超声作用于焊丝以及超声工具头作用于固体母材或者焊缝表面4种技术的各自特点及研究进展,着重分析了不同技术的设备特点及其对组织与力学性能的影响。最后对该方向的研究进展进行了总结,并对其发展前景和主要发展方向进行了展望。     

一种快速图像纹理分析算法

针对目前的纹理分析算法普遍存在计算复杂、运行时间过长的缺点,提出了一种新的图像纹理分析算法。该算法利用差分概念定义出图像的差分矩阵和差分直方图,并从差分直方图中提取特征进行图像纹理的相似度度量。由于本算法在考虑人类视觉特性的基础上尽量采用加减运算,因此不但具有与人类视觉特性相联系的特点,更使得算法的运行效率大大提高。使用本算法对brodatz 图像库进行的检索实验表明,该算法在查准率和检索效率上与共生矩阵算法相比分别提高13.9160%和 9.5 倍,具有与传统算法相比更好的检索效果和更高的检索效率。因此该算法可以满足实时性要求较高的场合,弥补了目前算法运行时间长的缺点。     

Time-varying autoregressive spectral estimation for ultrasound attenuation in tissue characterization

In the field of biological tissue characterization, fundamental acoustic attenuation properties have been demonstrated to have diagnostic importance. Attenuation caused by scattering and absorption shifts the instantaneous spectrum to the lower frequencies. Due to the time-dependence of the spectrum, the attenuation phenomenon is a time-variant process. This downward shift may be evaluated either by the maximum energy frequency of the spectrum or by the center frequency. In order to improve, in strongly attenuating media, the results given by the short-time Fourier analysis and the short-time parametric analysis, we propose two approaches adapted to this time-variant process: an adaptive method and a time-varying method. Signals backscattered by an homogeneous medium of scatterers are modeled by a computer algorithm with attenuation values ranging from 1 to 5 dB/cm MHz and a 45 MHz transducer center frequency. Under these conditions, the preliminary results obtained with the proposed time-variant methods, compared with the classical short-time Fourier analysis and the short-time auto-regressive (AR) analysis, are superior in terms of standard deviation (SD) of the attenuation coefficient estimate. This study, based on nonstationary AR spectral estimation, promises encouraging perspectives for in vitro and in vivo applications both in weakly and highly attenuating media.     

Application of the maximum entropy method in texture analysis

The problem of estimating the crystallite orientation distribution function (codf) based on the leading texture coefficients is considered. Problems of such a type are called moment problems, which are well known in statistical mechanics and other areas of science. It is shown how the maximum entropy method can be applied to estimate the codf. Special emphasis is given to a coordinate-free formulation of the problem. The codf is represented by a tensorial Fourier series. The equations, which have to be solved for the estimate of the distribution function, are derived for all tensor ranks of the Fourier coefficients. As a numerical example, a model codf is estimated based on a set of discrete crystal orientations given by a full-constrained Taylor type texture simulation.     

Measurements of surface texture using ultrasound

A new ultrasonic spectroscopic technique has been developed to measure the gross surface texture of materials. A surface roughness coefficient has been introduced that specifies the texture of a surface on a quantitative basis. Comprehensive theoretical models based on analyzing the frequency spectrum of the received ultrasonic signals have been developed to study the effect of surface texture on reflected ultrasonic pulses from rough surfaces. A minimization function obtains the best match between theoretical models and actual measurements in such a way that the resultant coefficient for the best match represents the surface roughness     

Application of solid-state NMR in characterization of bone related tissue engineering

Solid-state NMR has the potential to contribute to the quality of monitoring of the in growth of synthetic biomaterials in bone related tissue engineering. Severe experimental difficulties arise from the morphological diversity of bone, from the coexistence, interrelationship and great complexity of its organic and inorganic components, and lastly, from the substantial sensitivity of bone samples to physical and chemical effects. High-resolution solid-state NMR gives us the opportunity to look specifically at selected magnetic nuclei in whole bone without any chemical pretreatment, thus avoiding interference with bone structure. Solid-state NMR spectroscopy is thus an excellent tool to obtain such high-resolution information on bone samples not subjected to any chemical pretreatment. This short review has thus discussed current application of solid-state NMR in characterization of bone related tissue engineering.     

Controlled ultrasound tissue erosion

The ability of ultrasound to produce highly controlled tissue erosion was investigated. This study is motivated by the need to develop a noninvasive procedure to perforate the neonatal atrial septum as the first step in treatment of hypoplastic left heart syndrome. A total of 232 holes were generated in 40 pieces of excised porcine atrial wall by a 788 kHz single-element transducer. The effects of various parameters [e.g., pulse repetition frequency (PRF), pulse duration (PD), and gas content of liquid] on the erosion rate and energy efficiency were explored. An Isppa of 9000 W/cm2, PDs of 3, 6, 12, and 24 cycles; PRFs between 1.34 kHz and 66.7 kHz; and gas saturation of 40-55% and 79-85% were used. The results show that very short pulses delivered at certain PRFs could maximize the erosion rate and energy efficiency. We show that well-defined perforations can be precisely located in the atrial wall through the controlled ultrasound tissue erosion (CUTE) process. A preliminary in vivo experiment was conducted on a canine subject, and the atrial septum was perforated using CUTE.     

肝脏M型超声图像的包络提取及分析

肝脏在大血管搏动的激励下会产生运动,其运动情况可以反映肝脏硬化的程度,文章利用M型超声技术检测肝脏在这种激励下的运动信息,通过相关技术提取M型超声图像中肝脏的运动包络,并从中提取特性参数,用作肝硬化程度的诊断指标。     

Regularized autoregressive analysis of intravascular ultrasound backscatter: improvement in spatial accuracy of tissue maps

Autoregressive (AR) models are qualified for analysis of stochastic, short-time data, such as intravascular ultrasound (IVUS) backscatter. Regularization is required for AR analysis of short data lengths with an aim to increase spatial accuracy of predicted plaque composition and was achieved by determining suitable AR orders for short data records. Conventional methods of determining order were compared to the use of trend in the mean square error for determining order. Radio-frequency data from 101 fibrous, 56 fibro-lipidic, 50 calcified, and 70 lipid-core regions of interest (ROIs) were collected ex vivo from 51 human coronary arteries with 30 MHz unfocused IVUS transducers. Spectra were computed for AR model orders between 3-20 for data representing ROIs of two sizes (32 and 16 samples at 100 MHz sampling frequency) and were analyzed in the 17-42 MHz bandwidth. These spectra were characterized based on eight previously identified parameters. Statistical classification schemes were computed from 75% of the data and cross-validated with the remaining 25% using matched histology. The results determined the suitable AR order numbers for the two ROI sizes. Conventional methods of determining order did not perform well. Trend in the mean square error was identified as the most suitable factor for regularization of short record lengths.     

Intravascular ultrasound tissue harmonic imaging in vivo

Tissue harmonic imaging (THI) has been shown to increase image quality of medical ultrasound in the frequency range from 2 to 10 MHz and might, therefore, also be used to improve image quality in intravascular ultrasound (IVUS). In this study we constructed a prototype IVUS system that could operate in both fundamental frequency and second harmonic imaging modes. This system uses a conventional, continuously rotating, single-element IVUS catheter and was operated in fundamental 20 MHz, fundamental 40 MHz, and harmonic 40 MHz modes (transmit 20 MHz, receive 40 MHz). Hydrophone beam characterization measurements demonstrated the build-up of a second harmonic signal as a function of increasing pressure. Imaging experiments were conducted in both a tissue-mimicking phantom and in an atherosclerotic animal model in vivo. Acquisitions of fundamental 20 and 40 MHz and second harmonic acquisitions resulted in cross sections of the phantom and a rabbit aorta. The harmonic results of the imaging experiments showed the feasibility of intravascular THI with a conventional IVUS catheter both in a phantom and in vivo. The harmonic acquisitions also showed the potential of THI to reduce image artifacts compared to fundamental imaging.