Asymmetry of Doppler spectrum in stenosis differentiation

The asymmetry of the spectral distribution of ultrasonic Doppler flow velocity signals, assessed using the coefficient of skewness, is discussed as a criterion of stenosis differentiation. Its performance is compared with that of the index of turbulence intensity for both in vitro and in vivo flow Doppler signals, recorded distal to a stenosis. The power spectral distributions are computed using the direct Fourier transform and maximum likelihood method. The asymmetry of spectral distribution has proved to be a more efficient criterion than the turbulence intensity. The maximum likelihood method ensures better stenosis differentiation than the direct FFT method.     

基于小波变换的小鼠QRS复合波检测

采用二进小波变换与斜率和幅度相结合的方法，对小鼠QRS复合波进行检测。根据小鼠QRS复合波的特点，采用Daubechics小波为母函烽，按照ECG的频谱特点选用尺度因子，对有噪声污染和形态变异的QRS复合波进行了检测。结果表明：小波变换对小鼠QRS复合波的检测是一种有效的方法。     

MRI刚性平移运动模糊图像建模与恢复

磁共振成像过程中,患者的轻微运动可产生运动伪影。运动伪影会使MR图像模糊,从而影响医生对病灶区域的准确检测。传统抑制运动伪影的方法大多基于运动模型已知的情况下,忽略频率编码期间产生的运动,对K空间数据进行处理达到修正伪影的目的。本研究针对任意的刚性平移运动可由无数的匀速直线运动复合而成的特点,建立了匀速直线运动模糊图像的数学模型,并尝试在图像域内用状态空间的方法和Hough变换的理论进行处理,对小幅度水平匀速运动模糊图像的修正取得了满意的结果。在处理任意方向的匀速直线运动时,由于谱线在旋转时不可避免地进行近似插值处理,虽然校正后的图像也有较大的改善,但还有待进一步研究。另外,对较大幅度水平匀速运动模糊图像的修正,还需要寻求更好的方法来准确估计谱线中相邻暗线之间的距离。通过上述理论及实验的分析验证可以看出,本研究所提出的方法对处理MRI运动模糊图像的研究有一定的理论意义。     

A quantitative method for thein vitro study of sounds produced by prosthetic aortic heart valves Part II: an experimental,comparative study of the sounds produced by a normal and simulated-abnormal Starr-Edwards series 2400 aortic prosthesis

A comparative study was made of the sounds produced by a normal Starr-Edwards 2400 aortic valve prosthesis with those produced by the same valve but having a simulated overgrowth at the apex of the struts. Comparisons were made over the entire cardiac cycle for time and amplitude, power-density spectra, power-distribution spectra, power-distribution surfaces associated with individual valves, and three-dimensional power-distribution-difference surface. Power-density spectra were compared for portions of the cycle corresponding to the opening, systolic, and closing sounds of the valve. Physical parameters of an acoustical model were estimated from the power-density spectra. The results showed that each comparison gave information pertinent to the simulated malfunction. Opening. systolic and closing sounds, respectively, were different for each valve. The opening sound of the abnormal valve displayed a much lower frequency. Systolic sounds for the two valves were similar in frequency, but the normal valve produced more total power for this sound. The closing sound of the abnormal valve occurred later than that of the normal valve. These differences were more clearly seen when viewed in the frequency domain.     

A planar slab bidomain model for cardiac tissue

A fully three-dimensional model of the ventricular or atrial free wall will involve a planar geometry of finite thickness. The governing equations for the interstitial and extracellular potential of a planar slab of cardiac tissue comprised of parallel fibers undergoing uniform plane-wave activation are presented. A comparison with a bidomain of cylindrical geometry with the same half-thickness shows that the potentials in the planar bidomain (as a function of depth) approach core-conductor behavior more quickly.     

基于小波包变换的数字水印方法

提出了一种基于小波分析的盲图像水印方法,本方法.利用小波包分解在图像和音频文件中构造信息冗余,嵌入的水印为二值图像,提取时不需原始信息和水印信息.对比试验结果证明,该方法能够抵抗常见的水印攻击,在经过加噪、平滑、缩放和压缩等信号处理后仍能保持稳健.     

基于小波变换和拉普拉斯算子的细胞图像边缘检测方法

目的：介绍一种基于小波变换和拉普拉斯算子的血液细胞图像边缘识别方法。材料和方法：取正常人血样5mL。制成血液细胞图片12片，对血图像进行预处理后，利用小波变换的多分辨率特性滤除细胞图像中的干扰成份。根据血液细胞边缘附近的灰度分布梯度较大的特点，采用拉普拉斯算子及双阈值法对其进行边缘检测和识别。结果和结论：实验结果表明，结合小波变换和拉普拉斯算子的边缘提取算法对血液细胞图像边缘提取有良好的效果．为下一步对血液细胞的形态学分析、分类和识别提供了新途径。     

听觉诱发电位提取方法的研究与分析

论述了运用小波变换进行听觉诱发电佗单次提取的原理、方法和实验分析。结果表明，对单次试验信号，经小波变换及相关分析后，可从带自发脑电干扰的信号中提取诱发电位信号。小波变换分析方法与传统的叠加平均方法相比，可减少试验次数，缩短检测周期。     

自适应算法与小波变换在心电信号滤波中的应用

心电信号是一种基本的人体生理信号,具有重要的临床诊断价值。然而,体表检测人体心电信号中常带有工频干扰、基线漂移、肌电干扰等各种噪声,给临床对心血管疾病的诊断带来了障碍。为了消除心电信号检测过程中带有的上述三种噪声,采用LM S自适应算法及小波变换理论,有针对性的设计了自适应滤波器、小波变换滤波器和自适应信号分离器等三种数字滤波器来滤除相应干扰。结果表明,对心电信号中存在的这三种噪声具有很好的滤波效果。