一种用于测量胎儿心率的改进自相关算法

在围产期对肥儿心率进行监护是非常重要的，超声Doppler测量胎心率是最常用的无创方法。但是，由于Doppler信号成分很复杂，从而使信号处理比较困难。我们提出了一种改进的自相关方法－－指数加权自相关方法，并在其中利用了自己适应技术，通过临床试验发现，与以前的方法相比，使用这种方法从超声Doppler信号中提取的胎率较准确，尤其是在信号存在衰减和丢失的情况下。     

一种基于自相关和平均模差算法的胎儿心率提取方法

目的 胎儿心率是判断孕期胎儿健康状况的一项重要指标,使用超声多普勒测量胎心率是常用的无创方法.其中,自相关算法是常用的测量胎心率的算法,但是其抗噪性差,容易出错.方法 本文提出一种基于自相关与平均标准模差相结合的新算法,先通过自相关函数突显其周期性,然后用累计平均标准模差函数提取准确周期,最后通过使用该算法处理模拟器数据和临床数据,验证其精确度和抗噪性.结果 相比滑动窗算法,基于自相关和平均标准模差的算法具有更高的精确度和抗噪性.结论 改进后的算法可以有效计算出胎心率值.     

Passive fetal monitoring by adaptive wavelet denoising method

Fetal Heart Rate (FHR) monitoring is one of the most important fetal well being tests. Existing FHR monitoring methods are based on Doppler ultrasound technique, which has several disadvantages. Passive fetal monitoring by phonocardiography is an appropriate alternative; however, its implementation is a challenging task due to low energy of fetal heart sounds and multiple interference signals presence. In this paper, an advanced signal processing method for passive fetal monitoring based on adaptive wavelet denoising is presented. The method's performance is compared with Doppler ultrasound monitor. The results show 94-97.5% accuracy, including highly disturbed cases.     

基于coif5小波的多普勒胎心音信号提取算法的研究

胎心率监护是围产期胎儿监护的关键技术指标，超声多普勒测量胎心率是最常用的无创方法。由于胎心多普勒信号具有信噪比低、非平稳的随机性特点，提出基于coif5小波，结合双重阈值方法的胎心音信号提取算法。实验表明，该算法有效地解决了由于胎心率加倍、减半所引起的胎心率曲线翻转问题，提高了多普勒胎心音信号提取的准确性。     

The influence of coincidence of fetal and maternal QRS complexes on fetal heart rate reliability

Bioelectrical fetal heart activity being recorded from maternal abdominal surface contains more information than mechanical heart activity measurement based on the Doppler ultrasound signals. However, it requires extraction of fetal electrocardiogram from abdominal signals where the maternal electrocardiogram is dominant. The simplest technique for maternal component suppression is a blanking procedure, which relies upon the replacement of maternal QRS complexes by isoline values. Although, in case of coincidence of fetal and maternal QRS complexes, it causes a loss of information on fetal heart activity. Its influence on determination of fetal heart rate and the variability analysis depends on the sensitivity of the heart-beat detector used. The sensitivity is defined as an ability to detect the incomplete fetal QRS complex. The aim of this work was to evaluate the influence of the maternal electrocardiogram suppression method used on the reliability of FHR signal being calculated.     

Fetal responses to induced maternal relaxation during pregnancy

Fetal responses to induced maternal relaxation during the 32nd week of pregnancy were recorded in 100 maternal-fetal pairs using a digitized data collection system. The 18-min guided imagery relaxation manipulation generated significant changes in maternal heart rate, skin conductance, respiration period, and respiratory sinus arrhythmia. Significant alterations in fetal neurobehavior were observed, including decreased fetal heart rate (FHR), increased FHR variability, suppression of fetal motor activity (FM), and increased FM-FHR coupling. Attribution of the two fetal cardiac responses to the guided imagery procedure itself, as opposed to simple rest or recumbency, is tempered by the observed pattern of response. Evaluation of correspondence between changes within individual maternal-fetal pairs revealed significant associations between maternal autonomic measures and fetal cardiac patterns, lower umbilical and uterine artery resistance and increased FHR variability, and declining salivary cortisol and FM activity. Potential mechanisms that may mediate the observed results are discussed.     

Detection of fetal breathing and cardiac movements and rhythms in ultrasonic Doppler signal recorded on the surface of the maternal abdomen

It is proposed to use information on the direction of reflector movement and extensive filtering in the detection of fetal breathing and cardiac movements in the ultrasonic Doppler signal recorded on the surface of the material abdomen. The method appears fairly insensitive to spurious signals and allows those of interest to be distinguished without any reference technique. A decision rule for breathing and cardiac rhythm detection, incorporating movement direction, amplitude, shape and periodicity criteria, is also proposed.     

Compact long-term recorder for the transabdominal foetal and maternal electrocardiogram

Foetal heart rate (FHR) monitoring is a proven means of assessing foetal health during the antenatal period. Currently, the only widely available instrumentation for producing these data is based on Doppler ultrasound, a technology that is unsuitable for long-term use. For nearly a century, it has been known that the foetal electrocardiogram (FECG) can be detected using electrodes placed on the maternal abdomen. Although these signals suggest an alternative means of FHR derivation, their use has been limited owing to problems of poor signal-to-noise ratio. However, the eminent suitability of the transabdominal FECG for long-term FHR monitoring has suggested that perseverance with the technique would be worthwhile. The paper describes the design, construction and use of a compact, long-term recorder of three channels of 24 h antenatal transabdominal data. Preliminary use of the recorder in around 400 short recording sessions demonstrates that FHR records of equivalent quality to those from Doppler ultrasound-based instruments can be extracted from such data. The success of FHR derivation is, on average, around 65% of the recording period from around 20 weeks gestation (although this figure is reduced from around 28–32 weeks, and the success rates exhibit a wide range when individual subjects are considered). These results demonstrate that the technique offers, not only a means of acquiring long-term FHR data that are problematic to obtain by other means, but also a more patient-friendly alternative to the Doppler ultrasound technique.     

小波变换去噪方法在多谱勒胎儿心率提取中的应用研究

为了从超声多谱勒胎音信号中提取胎音信号，获得平滑的胎心率曲线，并计算胎心率，必须去除信号提取过程中的各种干扰和噪声。对平均频移算法获得的多谱勒信号的平均频率曲线采用小波变换中的五层强制去噪方法，使后续的相关计算能得到平滑的胎音信号，从而方便计算胎儿的心率。通过对实际超声多谱勒胎音信号的处理，获得了较好的结果，提取出了稳定、平滑的胎心率曲线，较准确地计算出了胎心率。     

Detection of atrial-flutter and atrial-fibrillation waveforms by fetal magnetocardiogram

Two cases of fetal tachycardia are reported: atrial flutter and fibrillation. The waveforms from each case were detected by fetal magnetocardiograms (FMCGs) using a 64-channel superconducting quantum interference device (SQUID) system. Because the magnitude of supraventricular arrhythmia signals is very weak, two subtraction methods were used to detect the fetal MCG waveforms: subtraction of the maternal MCG signal, and subtraction of the fetal QRS complex signal. It was found that atrial-flutter waveforms showed a cyclic pattern and that atrial-fibrillation waveforms showed f-waves with a random atrial rhythm. Fast Fourier transform analysis determined the main frequency of the atrial flutter to be about 7 Hz, and the frequency distribution of atrial fibrillation consisted of small, broad peaks. To visualise the current pattern, current-arrow maps, which simplify the observation of pseudo-current patterns in fetal hearts, of the averaged atrial flutter and fibrillation waveforms were produced. The map of the atrial flutter had a circular pattern, indicating a re-entry circuit, and the map of the atrial fibrillation indicated one wavelet, which was produced by a micro-re-entry circuit. It is thus concluded that an FMCG can detect supraventricular arrhythmia, which can be characterised by re-entry circuits, in fetuses.     

Computer method for perinatal screening of cardiac murmur using fetal phonocardiography

The main purpose of this paper is to demonstrate the capability of fetal phonocardiographic measurements to indicate some congenital heart defects. It deals with the results of investigations carried out during the last four years involving 820 pregnant women. During the investigations fetal cardiac murmurs presenting typical waveforms and incidences of acoustic signals were recorded. Causes of these murmurs are suggested based on comparison with the well-known waveforms of infants and children. A sophisticated signal processing method for murmur discovery is presented, that is also useful for automatic perinatal screening after the 28th week of gestation. By these means low-risk population may also be fully tested for cardiac malfunctions.     

A mathematical model for simulation of early decelerations in the cardiotocogram during labor

Fetal welfare during labor and delivery is commonly monitored through the cardiotocogram (CTG), the combined registration of uterus contractions and fetal heart rate (FHR). The CTG gives an indication of the main determinant of the acute fetal condition, namely its oxygen state. However, interpretation is complicated by the complex relationship between the two. Mathematical models can be used to assist with the interpretation of the CTG, since they enable quantitative modeling of the cascade of events through which uterine contractions affect fetal oxygenation and FHR. We developed a mathematical model to simulate 'early decelerations', i.e. variations in FHR originating from caput compression during uterine contractions, as mediated by cerebral flow reduction, cerebral hypoxia and a vagal nerve response to hypoxia. Simulation results show a realistic response, both for fetal and maternal hemodynamics at term, as for FHR variation during early decelerations. The model is intended to be used as a training tool for gynaecologists. Therefore 6 clinical experts were asked to rate 5 real and 5 model-generated CTG tracings on overall realism and realism of selected aspects. Results show no significant differences between real and computer-generated CTG tracings.     

音频多普勒信号的多特征分类决策

本文将音频多普勒信号的几种特征提取方法结合起来 ,用多元分析的方法对血流状况进行多特征的分类决策 ,所用的特征提取方法包括 :传统的声谱参数法 ,音频信号的零极点模型法 ,分形特征分析法及Teager能量法。将这种多特征分类决策法用于 71例胎儿脐血流音频多普勒信号的分析 ,结果表明 :该方法对胎儿宫内异常等疾病具有敏感性 ,可望为医学临床提供辅助诊断手段     

一种便携式多普勒胎心检测系统的设计及实现

本研究设计并实现了一款便携式,全数字,用于围产期胎儿心率检测的多普勒胎心系统,其采用对超声回波加窗,数字相乘等方法获取频移信号,并可对特定组织深度进行运动检测。该系统由CPLD超声激励及采集电路、MCU及外围电路和系统软件三部分组成。与两款商用胎心仪相比,本系统准确度较高,能够稳定可靠的对胎心进行检测。     

一种基于单通道腹部信号的胎儿心电提取算法

设计一种基于单通道孕腹部信号的胎儿心电提取算法,分别提取出母亲心电和胎儿心电,并计算出母亲心率和胎儿心率。首先对单通道孕腹部信号进行k-TEO(k=19)变换,突出母亲心电的QRS波,从而通过简单的阈值法确定母亲心电的R波位置,接着通过在相邻R波间重采样以获得相同的R-R间期T,这样经过一个间隔为T的梳状滤波器就可以分离出相同R-R间期的母亲心电,然后再一次在相邻R波间进行重采样恢复原来的R-R间期就可以获得实际的母亲心电了。原始腹部信号减去上面提取的母亲心电后,胎儿心电QRS波的信噪比大大提高,通过再次应用提取母亲心电的算法即可得到“干净”的胎儿心电波形。选取Physionet数据库中的8 组(26 通道)孕腹部信号数据进行分析,计算每个通道数据的胎儿心电QRS波位置识别灵敏度、阳性检测率和准确性。结果表明,胎儿心电QRS波的识别准确率达到87.1%,其中有6 个通道达到100%。另外计算每个通道的母亲心率和胎儿心率并做统计分析,发现每一组中各个通道的母亲平均心率和胎儿平均心率都非常接近,同一组中各通道间母亲平均心率最大误差为0.1次/min, 而胎儿平均心率最大误差也只有0.9次/min,进一步证明算法的可靠性。     

组织多普勒成像超声检测在胎儿心律失常诊断中的应用

目的探讨组织多普勒成像超声检测在胎儿心律失常诊断中的价值。方法采用组织多普勒成像（TDI）对100例孕妇进行组织多普勒成像超声检测,测量房室传导时间（AV）及心室开始收缩至下一心动周期心房开始收缩的时间间期（VA）。均测量3个心动周期,取平均值。对于偶发心律失常的胎儿,测量AV、VA时,取心律失常前或后至少3个窦性心动周期以外开始测量;同时测量心律失常时的AV、VA并与自身窦性心率进行比较。结果 （1）100例胎儿的心脏传导时间均被成功测量,心脏结构均正常,心律正常88例,偶发心律失常12例。AV、VA与心率呈负相关,AV在不同心率胎儿的比较差异无统计学意义（P〉0.05）,VA在不同心率胎儿的比较差异有统计学意义（P〈0.05）。（2）AV、VA与心率呈负相关。AV在不同心率胎儿的比较差异无统计学意义（P〉0.05）,VA在不同心率胎儿的比较差异有统计学意义（P〈0.05）。（3）12例偶发心律失常胎儿心脏结构正常。4例为心动过缓胎儿中,1例表现为AV、VA均明显延长,l例AV明显延长,2例VA明显延长。8例为房型期前收缩,其中2例为二联律,早搏周期VA均较窦性心率时缩短,其后代偿间歇周期的VA除2例外均明显延长,早搏周期AV、代偿间歇周期AV与窦性心动周期的AV相比无明显改变。结论组织多普勒成像超声检测对产前超声筛查胎儿心律失常方面具有重要的作用和临床意义。结论组织多普勒成像可简单快速地定量测定胎儿心脏传导时间,对产前超声筛查胎儿心律失常方面具有重要的作用和临床意义。     

Recording and processing of fetal movements and sounds obtained with the Inpho inductive transducer

A recently developed transducer based on an inductive principle allows recording of fetal displacement signals on the maternal abdominal wall. The transducer is a relatively passive device, in contrast to commonly applied ultrasound transducers. This permits long-term observation of fetal movements and sounds. The bandwidth of the system is DC −200 Hz (±3dB), and signal-to-noise ratios of more than 96 dB have been measured in a laboratory setup, whereas in the practical situation a signal-to-noise ratio of 78 dB has been established. The transducer has been applied to study fetal respiratory sinus arrhythmia, which means that fetal breathing movements have to be extracted from the transducer's output. This proved possible by digital filtering of the displacement signal as detected by the transducer. The transducer has also been applied in a study where the signal-to-noise ratio of fetal heart sounds as a function of location of the fetus and position of the transducer on the maternal abdominal wall has been studied. It proved possible to adequately record fetal heart sounds for measurement of fetal heart rate. Also uterine activity could be recorded using the sensor's DC output.     

Preservation of quadrature Doppler signals from bidirectional slow blood flow close to the vessel wall using an adaptive decomposition algorithm

A novel approach based on the phasing-filter (PF) technique and the empirical mode decomposition (EMD) algorithm is proposed to preserve quadrature Doppler signal components from bidirectional slow blood flow close to the vessel wall. Bidirectional mixed Doppler ultrasound signals, which were echoed from the forward and reverse moving blood and vessel wall, were initially separated to avoid the phase distortion of quadrature Doppler signals (which is induced from direct decomposition by the nonlinear EMD processing). Separated unidirectional mixed Doppler signals were decomposed into intrinsic mode functions (IMFs) using the EMD algorithm and the relevant IMFs that contribute to blood flow components were identified and summed to give the blood flow signals, whereby only the components from the bidirectional slow blood flow close to the vessel wall were retained independently. The complex quadrature Doppler blood flow signal was reconstructed from a combination of the extracted unidirectional Doppler blood flow signals. The proposed approach was applied to simulated and clinical Doppler signals. It is concluded from the experimental results that this approach is practical for the preservation of quadrature Doppler signal components from the bidirectional slow blood flow close to the vessel wall, and may provide more diagnostic information for the diagnosis and treatment of vascular diseases.     

Measurement of fetal movements using multichannel ultrasound pulsed Doppler: Autorecognition of fetal movements by maximum entropy method

Changes in fetal movements indicate biophysical conditions and functional development. The precise evaluation of fetal movements in clinical medicine requires the development of a continuous automated monitoring technique. A basic study of the measurement of fetal movements was carried out by modifying the Doppler ultrasound module of a cardiotocograph to produce low-frequency Doppler signals and five simultaneous outputs at various depths. These outputs represent displacement inside tissue at the various depths. Signal processing was executed on a 32-bit computer with a high-accuracy displacement estimation technique using the arctangent method. Results showed successful tracking of minute movements, such as fetal breathing movements (FBM), while rejecting other movements derived from maternal breathing etc. Using spectral analysis by the maximum entropy method (MEM), fetal movements were classified in three groups (FBM, fetal gross movements (FGM) and fetal heart movements (FHM)), based on the character of their special peak frequencies. The order of movement recognition was first FGM, then FBM and lastly FHM. FBM were more successfully recognised by MEM than by conventional B-mode observation methods. Small body movements were difficult to recognise as FGM by MEM in some cases. Although further studies are required for clinical application, it appears that automated assessments of fetal movements should be possible with this technique.