基于小波变换过零点表征的脉搏信号分析

目的 探索中医脉诊客观化的新方法。方法 根据小波变换过零点和信号突变点之间的关系．分别运用小波变换过零点表征检测脉象时域特征点和各特征点脉搏信号变化的快慢。结果 通过对20例健康人和20例孕妇脉象时域特征点过零点位置的统计及其变化快慢的计算,分析结果正好与实际相吻合。结论 应用这种方法可以比较准确地分析脉象信号所携带的大量生理信息,从而为中医脉诊客观化提供了一种新方法。     

二项式小波检测心电特征点

目的 使用二项式小波检测心电信号的特征点,为心电信号的分析提供新的检测手段。方法 设计对称形式的二项式小波,应用它对实际心电信号进行小波变换,并进行特征点的检测,观察检测效果。结果 使用二项式小波检测心电特征点方法实现简单,对试验心电信号的特征点定位准确,快速。结论 对称形式的二项式小波检测较其他小波检测方法简单,无须预处理,有良好的临床应用价值,在心电信号的实时分析中也有很好的应用前景。     

基于小波变换和K-means聚类算法的心电信号特征提取

目的研究一种基于小波变换和K-means聚类算法的心电信号特征提取方法,根据特征点信息判断心电是否正常。方法利用小波变换和形态学滤波方法去除工频干扰、肌电干扰和基线漂移等主要的噪声之后,利用K-Means聚类算法提取出心电信号的QRS波群,P波和T波这3个主要的特征点,实现心电智能诊断。结果实验数据取自MIT-BIH数据库,多次实验结果显示QRS波群的阳性检测度(P+)达到99.68%和灵敏度(Se)达到99.21%,P波和T波的检测准确度分别达91.43%和97.01%。结论相对于其它方法,本文心电特征提取方法准确度较高,具有一定参考价值;在移动医疗和临床医疗方面具有一定实用价值。     

基于小波变换模板的QRS检测方法

目的 有效提高QRS复合波的检测率。方法 ECG信号经过小波变换后，其不同频率成份会映射到变换结果的不同尺度上，而在这些尺度之间存在相互的联系。本文正是利用小波变换后尺度之间的相互关系，提出了一种基于墨西哥草帽小波变换不同尺度之间关系的ECG信号QRS复合波检测方法。该方法根据变换结果的特征点提取小波变换模板，并将这个模板用于ECG信号的QRS检测，可以在滤除噪声的同时，有效提高检测率。结果 经MIT／BIH标准心电数据库检测验证，QRS波正确检测率达到99．9％。结论 综合利用小波变换不同尺度进行非线性变换所得到的模板可以显著提高QRS复合波的检测率。     

基于能量变换与小波分解的QRS波群检测算法

目的 使用能量变换与小波分解的联合算法检测心电信号QRS波群的特征点,为心电信号的自动分析提供新的手段.方法 能量变换是基于信号的局部特征的,可以有效地突出信号的峰点或谷点;小波分解对信号做多分辨率分解,可以突出信号的特征信息;两种方法的结合更利于QRS波群的检测.结果 使用30例样本检测算法性能,证明联合算法能够提高信噪比,对特征点的定位准确可靠.经MIT/BIH心电数据库的检测验证,其R波定位的正确率高达99.79%.使用心率趋势图分析计算结果,不仅可以完全纠正误检和漏检,而且能够定位异常的心搏.结论 本算法能够准确、实时地识别被噪声严重干扰的心电信号的QRS波群,因而在心电信号的自动分析中有很好的应用前景.     

利用小波级数检测癫痫EEG中的棘波

目的 研究自动提取癫痫脑电中棘波。方法 把ＥＥＧ信号分解成小波级数，在各个尺度上，利用信号细节在两个过零点之间的平均振幅确定瞬态波形的大小，通过选择平均振幅中的局部极值检测刺波。结果 对６位患者的ＥＥＧ信号进行处理，检测刺波的正确率为９６．６６％，结论 这种方法能够比较准确地检测ＥＥＧ中的棘波。     

结合静态小波变换的自适应窗口可除颤节律检测

目的为克服固定时间窗口分段导致R波截断的缺点,提出一种新的分段方法——固定R波个数的自适应窗口分段法,用于可除颤节律检测。方法首先用波谷波峰法定位ECG信号R波,以5个R波长度为窗口大小自适应分段ECG信号,得到每段信号能量、复杂度、时间长度时域特征;其次再对每段信号进行静态小波变换,获取每层小波系数与原始分段信号的相关系数时频特征;最后混合时域、时频域两类特征,输入到支持向量机、k-近邻、随机森林分类器进行信号分类,实现可除颤节律检测。结果在CUDB和VFDB两个开源数据库上对新算法进行验证比较,其准确率最高分别为:98.12%、97.19%;敏感度最高分别为:97.20%、95.88%;特异性最高分别为:98.72%、97.96%。结论新算法能够很好地实现可除颤节律的检测。     

环境因素对暖体假人模拟潮湿服装的蒸发散热性能分析

目的 针对心音信号为便捷有效地识别肥心病心音与正常心音,研究基于WER-PCA的肥心病心杂音特征提取算法。方法 应用小波变换获得10维重构信号,应用主成分分析（PCA）筛选出肥心病心杂音频段对应的小波分解特定层,提取心杂音频段的小波能量百分比,将其与正常心音的差异度相组合作为肥心病心音特征。结果 对168例正常心音和194例肥心病心音进行识别,正常心音与肥心病心音最优识别正确率为95.3%,验证了提取出的特征的有效性。结论 该算法能有效提取肥心病心杂音特征识别肥心病,研究提出的心杂音特定频带可以为后续研究肥心病病症提供有效的参考诊断指标与方法。     

基于WER-PCA的肥心病心杂音特征提取算法研究

目的为便捷有效地识别肥心病心音与正常心音,针对心音信号研究基于WER-PCA的肥心病心杂音特征提取算法。方法采集168例正常心音信号和194例肥心病心音信号,应用小波变换获得10维重构信号,应用主成分分析筛选出肥心病心杂音频段对应的小波分解特定层,提取心杂音频段的能量百分比,将其与正常心音的差异度相组合作为肥心病心音特征。结果对比正常心音与肥心病心音主成分构成元素,筛选出肥心病心杂音频带范围为86.15～689.05Hz;对正常心音和肥心病心音进行识别,差异度结合能量的识别特征,其最优识别正确率为95.3%。结论该算法能有效提取肥心病心杂音特征以识别肥心病。     

自发耳声发射信号检测方法的研究

目的 探讨对自发耳声发射信号进行较高分辨率和准确率的稳健检测算法以使其应用于临床。方法 采用改进的周期图法、ＡＲ模型及小波变换方法，研究自发耳声发射信号的检测算法。结果 改进的周期图法和小波变换方法比目前临床所采用的检测算法在准确检测谱峰峰值及其位置、高分辨率提取信号频谱特征等人有更大的优越性。结论 改进的周期图法和小波变换方法对推动自发耳声发射在临床生理和病理上的应用有巨大的潜力。     

Nontriggered MRI quantification of aortic pulse‐wave velocity

Pulse‐wave velocity is an index of arterial stiffness, which is a strong indicator of cardiovascular risk. We present a high‐speed technique that generates time‐resolved complex difference signal intensity simultaneously in the ascending and descending aorta from velocity‐encoded projections without gating, allowing quantification of pulse‐wave velocity. The velocity‐time curve was approximated with a time‐resolved complex difference signal intensity to estimate the propagation time of the pulse wave in the aortic arch. The path length of the pulse wave is measured from an oblique sagittal image in a plane encompassing thoracic ascending and descending aorta, and pulse‐wave velocity is computed from the ratio between the path length and pulse‐wave propagation time. The method was implemented at 1.5 T and 3 T, and pulse‐wave velocity was quantified in healthy subjects (ages 20–70 years, N = 23) without symptoms or prior history of cardiovascular events. In addition, the method was compared against retrospectively EKG‐gated PC‐MRI. The overall results were found to be in good agreement with literature data showing age‐related increase in aortic stiffness. The RMS differences between the projection and gated PC‐MRI methods were less than 4%. Key benefits of the proposed method are simplicity in both data acquisition and processing requiring only computation of the complex difference between the velocity‐encoded projections rather than absolute velocity. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

Estimation of local aortic elastic properties with MRI.

Aortic compliance and pulse wave velocity (PWV) are important determiners of heart load, and are clinically useful indices of cardiovascular risk. Most direct methods to derive them require invasive pressure measurement. In this work a noninvasive technique to evaluate aortic compliance and PWV using MRI is proposed. MRI magnitude and phase images to measure area and flow in the ascending aorta were acquired in a group of 13 young healthy subjects. Assuming that the early systolic part of the wave was unidirectional and reflectionless, PWV was determined as the ratio between flow and area variations at early systole. Our results were compared to pulse wave velocities derived from a direct transit time, and to one using ascending aortic area and peripheral brachial pulse pressure. The new method proved to be accurate and in good agreement with the transit time method, as well as with previously published results.     

Alternate ascending/descending directional navigation approach for imaging magnetization transfer asymmetry

A new method for imaging magnetization transfer (MT) asymmetry with no separate saturation pulse is proposed in this article. MT effects were generated from sequential two‐dimensional balanced steady‐state free precession imaging, where interslice MT asymmetry was separated from interslice blood flow and magnetic field inhomogeneity with alternate ascending/descending directional navigation (ALADDIN). Alternate ascending/descending directional navigation provided high‐resolution multislice MT asymmetry images within a reasonable imaging time of ～3 min. MT asymmetry signals measured with alternate ascending/descending directional navigation were 1–2% of baseline signals (N = 6), in agreement with those from the conventional methods. About 70% of MT asymmetry signals were determined by the first prior slice. The frequency offset ranges in this study were >8 ppm from the water resonance frequency, implying that the MT effects were mostly associated with solid‐like macromolecules. Potential methods to make alternate ascending/descending directional navigation feasible for imaging amide proton transfer (～3.5 ppm offset from the water resonance frequency) were discussed. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

小波尺度图分析法及其在超声血流多普勒信号中的应用

目的 将现代小波尺度图分析方法应用到人体血流多普勒信号的谱估计之中,计算血流多为勒信号的功率谱,得到小波意义上的尺度图。方法 从时频分布的观点,小波尺度图是一种仿射平滑的Ｗｉｇｎｅｒ－Ｖｉｌｌｅ分布,具有恒“Ｑ”特性的时间频率分析窗,对于人体颈总动脉的仿真多普勒血流信号,进行了小波尺度图的研究。结果 通过血流多普勒信号的小波尺度图研究,发现利用小波尺度图可心提高血流多普勒信号低步 段的频谱分辨率,     

In vivo measurement of local aortic pulse‐wave velocity in mice with MR microscopy at 17.6 tesla

Transgenic mouse models of human diseases have gained increasing importance in the pathophysiology of cardiovascular diseases (CVD). As an indirect measure of vascular stiffness, aortic pulse‐wave velocity (PWV) is an important predictor of cardiovascular risk. This study presents an MRI approach that uses a flow area method to estimate local aortic pulse‐wave velocity at different sites in the murine aorta. By simultaneously measuring the cross‐sectional area and the through‐plane velocity with a phase‐contrast CINE method, it was possible to measure average values for the PWV in the ascending and descending aorta within the range of 2.4–4.3 m/s for C57BL/6J mice (ages 2 and 8 months) and apoE‐knockout mice (age 8 months). Statistically significant differences of the mean values of the PWV of both groups could be determined. By repeating CINE measurements with a time delay of 1 ms between two subsequent data sets, an effective temporal resolution of 1000 frames/s (fps) could be achieved. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

A new method for the determination of aortic pulse wave velocity using cross-correlation on 2D PCMR velocity data

PURPOSE: To evaluate the reproducibility of a new multisite axial pulse wave velocity (PWV) measurement technique that makes use of 2D PCMR data and cross-correlation analysis. MATERIALS AND METHODS: PWV was estimated with MRI in 13 healthy volunteers by a transit-time technique (TT), a multisite technique utilizing 1D PCMR data in the descending aorta (FOOT), and a new multisite axial technique that uses 2D PCMR data over the ascending, transverse, and descending sections of the aorta (2D-XC). RESULTS: No significant difference was observed between PWV measurements values measured by the three techniques. However, 2D-XC displayed significantly better intertest reproducibility than either the TT or FOOT methodologies. Average percent difference between scans: TT: 15.8% +/- 13.4%, FOOT: 21.3% +/- 16.9%, 2D-XC: 7.72% +/- 4.73%. P = 0.02 for both 2D-XC/TT comparison and 2D-XC/FOOT comparison. CONCLUSION: 2D-XC is a more reproducible method than either the established TT or FOOT methods to estimate the aortic PWV.     

力竭性运动前后的脉图观察研究

对３７名男性志愿者进行力竭性运动前后生理、生化指标的变化进行测定，并同步对其桡动脉脉图进行检测记录。结果显示：在力竭性运动后ＤＢＰ、ＬＤＨ、ＣＫ变化显著（与运动前比较均Ｐ＜０．０１）；脉图波形变化表现为，主波宽度增加，降中峡降低，波形面积减小；脉图指标ｈ４／ｈ１、ｗ／ｔ、Ｓ、ｔ１／ｔ较运动前均有显著变化（均Ｐ＜０．００１）；脉图生物龄比运动前平均增大１４．９６岁。结果表明，力竭性运动前后，脉图指标与生化指标均有显著变化，通过对运动脉图的观察研究，可以尝试建立一种无创的机能评价方法。     

Implementation of three‐dimensional wavelet encoding spectroscopic imaging: In vivo application and method comparison

We have recently proposed a two‐dimensional Wavelet Encoding‐Spectroscopic Imaging (WE‐SI) technique as an alternative to Chemical Shift Imaging (CSI), to reduce acquisition time and crossvoxel contamination in magnetic resonance spectroscopic imaging (MRSI). In this article we describe the extension of the WE‐SI technique to three dimensions and its implementation on a clinical 1.5 T General Electric (GE) scanner. Phantom and in vivo studies are carried out to demonstrate the usefulness of this technique for further acquisition time reduction with low voxel contamination. In wavelet encoding, a set of dilated and translated prototype functions called wavelets are used to span a localized space by dividing it into a set of subspaces with predetermined sizes and locations. In spectroscopic imaging, this process is achieved using radiofrequency (RF) pulses with profiles resembling the wavelet shapes. Slice selective excitation and refocusing RF pulses, with single‐band and dual‐band profiles similar to Haar wavelets, are used in a modified PRESS sequence to acquire 3D WE‐SI data. Wavelet dilation and translation are achieved by changing the strength of the localization gradients and frequency shift of the RF pulses, respectively. The desired spatial resolution in each direction sets the corresponding number of dilations (increases in the localization gradients), and consequently, the number of translations (frequency shift) of the Haar wavelets (RF pulses), which are used to collect magnetic resonance (MR) signals from the corresponding subspaces. Data acquisition time is reduced by using the minimum recovery time (TR_min), also called effective time, when successive MR signals from adjacent subspaces are collected. Inverse wavelet transform is performed on the acquired data to produce metabolite maps. The proposed WE‐SI method is compared in terms of acquisition time, pixel bleed, and signal‐to‐noise ratio to the CSI technique. The study outcome shows that 3D WE‐SI provides accurate results while reducing both acquisition time and voxel contamination. Magn Reson Med 61:6–15, 2009. © 2008 Wiley‐Liss, Inc.