Autoregressive spectral estimation of fetal breathing movement

Fetal breathing movement (FBM) in utero may be an indicator of fetal health. This paper provides a second-by-second estimate of FBM rate. In the absence of a statistical model for the fetal breathing movement, block data structured autoregressive spectral estimation is used. The optimum tapered Burg algorithm provides a minimum variance breathing rate estimate from a short block of data. The data were recorded using a PVDF (PolyVinyliDeneFluoride) transducer which picks up maternal abdominal wall movements. A peak tracking algorithm is used to extract the fetal breathing rate. Results from these signals are presented in graphical form. Further analysis of the fetal breathing rate has revealed periodicities, similar to that observed in the fetal heart rate.     

Measurement of Fetal Movements by Moving-Coil Transducer

A transducer for the detection of fetal movements is described. The transducer is based on a coil moving in a magnetic field. It produces a signal as a result of fetal movements which create changes on the matemal anterior abdomen. The transducer is not affected by slow movements, maternal respiration, and uterine contractions. The sensitivity of the transducer in comparison with other means of fetal movement assessment is discussed.     

The Measurement of Fetal Movement Using a Strain-Gauge Transducer

Strain-gauge transducers are a simple and safe means of measuring fetal movement. The transducers do, however, respond to all abdominal movement and thus the measuring instrument must discriminate between maternal and fetal movements. The discrimination may be achieved by choosing an appropriate size for the transducer and also by using an adaptive filter. The success of the adaptive filter is illustrated on real data.     

A Tracking System for Pulsed Ultrasound Images: Application to Quantification of Fetal Breathing Movements

A tracking system for quantification of moving structures from a real-time B-scan ultrasound image is described. The system provides a hard copy tracing of the movements with a resolution that is uncoupled from the wavelength of the ultrasound frequency employed. In the present instrument, a laboratory resolution of 0.06 mm and a differential target velocity of 961 mm/s has been achieved which has been more than adequate for tracking and recording all observed fetal movements, including the relatively high speed fetal hiccough. Both mechanical target tests and in vivo fetal breathing movements associated with maternal glucose loading are reported herein.     

Extraction of fetal electrocardiogram using adaptive neuro-fuzzy inference systems

In this paper, we investigate the use of adaptive neuro-fuzzy inference systems (ANFIS) for fetal electrocardiogram (FECG) extraction from two ECG signals recorded at the thoracic and abdominal areas of the mother's skin. The thoracic ECG is assumed to be almost completely maternal (MECG) while the abdominal ECG is considered to be composite as it contains both the mother's and the fetus' ECG signals. The maternal component in the abdominal ECG signal is a nonlinearly transformed version of the MECG. We use an ANFIS network to identify this nonlinear relationship, and to align the MECG signal with the maternal component in the abdominal ECG signal. Thus, we extract the FECG component by subtracting the aligned version of the MECG signal from the abdominal ECG signal. We validate our technique on both real and synthetic ECG signals. Our results demonstrate the effectiveness of the proposed technique in extracting the FECG component from abdominal signals of very low maternal to fetal signal-to-noise ratios. The results also show that the technique is capable of extracting the FECG even when it is totally embedded within the maternal QRS complex.     

Detection of Fetal Heart Rate Through 3-D Phase Space Analysis From Multivariate Abdominal Recordings

A novel three-stage methodology for the detection of fetal heart rate (fHR) from multivariate abdominal ECG recordings is introduced. In the first stage, the maternal R-peaks and fiducial points (maternal QRS onset and offset) are detected, using band-pass filtering and phase space analysis. The maternal fiducial points are used to eliminate the maternal QRS complexes from the abdominal ECG recordings. In the second stage, two denoising procedures are applied to enhance the fetal QRS complexes. The phase space characteristics are employed to identify fetal heart beats not overlapping with the maternal QRSs, which are eliminated in the first stage. The extraction of the fHR is accomplished in the third stage, using a histogram-based technique in order to identify the location of the fetal heart beats that overlap with the maternal QRSs. The methodology is evaluated on simulated multichannel ECG signals, generated by a recently proposed model with various SNRs, and on real signals, recorded from pregnant women in various weeks during gestation. In both cases, the obtained results indicate high performance; in the simulated ECGs, the accuracy ranges from 72.78% to 98.61%, depending on the employed SNR, while in the real recordings, the average accuracy is 95.45%. The proposed methodology is advantageous since it copes with the existence of noise from various sources while it is applicable in multichannel abdominal recordings.      

简单导联胎儿心电信号提取的程控放大器设计

为构建简单导联胎儿心电信号提取系统,提出一种基于简单导联的前端微弱信号程控放大器设计方法。设计中引入自动增益控制（AGC）方法,在满足输出信号幅度相对稳定的情况下,调整总放大倍数在10000倍范围内变化。自动记录信号和放大倍数的拟合关系,自动增益控制范围可达69dB,保证了在母体腹壁混合信号采集时,细节信号不丢失,便于微弱胎儿心电信号的恢复。工程应用测试表明,设计的放大器用于胎儿心电信号提取时,可以提取出清晰胎儿心电。     

A successive cancellation algorithm for fetal heart-rate estimation using an intrauterine ECG signal

In this paper, we present a two-stage successive cancellation (SC) algorithm that sequentially separates fetal and maternal heartbeats from an intrauterine electrocardiogram (IuECG) signal containing both fetal and maternal QRS complexes. The ECG signal is modeled as a series of fetal, maternal, and noise events. Peak detection is first employed to locate the potential fetal and maternal QRS complexes, referred to as candidate events. Each stage automatically generates a template of a source from the candidate events in the initialization period, and thereafter performs classification of the remaining candidate events based on a template matching technique. The detected events of the stronger signal are subtracted from the composite ECG signal prior to initialization and classification of the weaker signal. Once the fetal and maternal complexes are successfully detected and separated, a counting mechanism is utilized to derive the corresponding heart rates. Computer simulation results on real IuECG data demonstrate the effectiveness of the SC algorithm.     

A new method for the extraction of fetal ECG from the composite abdominal signal

We developed a wavelet transform-based method to extract the fetal electrocardiogram (ECG) from the composite abdominal signal. This is based on the detection of the singularities obtained from the composite abdominal signal, using the modulus maxima in the wavelet domain. Modulus maxima locations of the abdominal signal are used to discriminate between maternal and fetal ECG signals. Two different approaches have been considered. In the first approach, at least one thoracic signal is used as the a prior to perform the classification whereas in the second approach no thoracic signal is needed. A reconstruction method is utilized to obtain the fetal ECG signal from the detected fetal modulus maxima. The proposed technique is different from the classical time-domain methods, in that we exploit the most distinct features of the signal, leading to more robustness with respect to signal perturbations. Results of experiments with both synthetic and real ECG data have been presented to demonstrate the efficacy of the proposed method.     

An automated methodology for fetal heart rate extraction from the abdominal electrocardiogram.

This paper introduces an automated methodology for the extraction of fetal heart rate from cutaneous potential abdominal electrocardiogram (abdECG) recordings. A three-stage methodology is proposed. Having the initial recording, which consists of a small number of abdECG leads in the first stage, the maternal R-peaks and fiducial points (QRS onset and offset) are detected using time-frequency (t-f) analysis and medical knowledge. Then, the maternal QRS complexes are eliminated. In the second stage, the positions of the candidate fetal R-peaks are located using complex wavelets and matching theory techniques. In the third stage, the fetal R-peaks, which overlap with the maternal QRS complexes (eliminated in the first stage) are found using two approaches: a heuristic algorithm technique and a histogram-based technique. The fetal R-peaks detected are used to calculate the fetal heart rate. The methodology is validated using a dataset of eight short and ten long-duration recordings, obtained between the 20th and the 41st week of gestation, and the obtained accuracy is 97.47%. The proposed methodology is advantageous, since it is based on the analysis of few abdominal leads in contrast to other proposed methods, which need a large number of leads.     

基于MSP430和USB的胎儿心电图仪的设计

介绍一种基于MSP430单片机和USB总线的胎儿心电图仪,并给出其硬件电路和软件设计方法。系统采用TI公司超低功耗单片机MSP430F149对母体腹部和胸部心电信号进行同步采集,并通过USB接口将数据发送到PC机,利用上位机软件完成处理、显示、存储等。系统性能可靠、使用方便、结构简单、成本低廉。     

Evaluation of Autocorrelation Techniques for Detection of the Fetal Electrocardiogram

This paper presents an evaluation of autocorrelation techniques for the detection of fetal electrocardiogram signals from abdominal recordings. Raw signals are digitized, then processed and analyzed by a digital computer. The effect of elimination of the maternal signal and of fluctuations in the fetal period is demonstrated. Correlation parameters such as length of signal and sampling rate are investigated.     

Fetal ECG extraction from single-channel maternal ECG usingsingular value decomposition

The extraction of fetal electrocardiogram (ECG) from the composite maternal ECG signal obtained from the abdominal lead is discussed. The proposed method employs singular value decomposition (SVD) and analysis based on the singular value ratio (SVR) spectrum. The maternal ECG (M-ECG) and the fetal ECG (F-ECG) components are identified in terms of the SV-decomposed modes of the appropriately configured data matrices, and elimination of the M-ECG and determination of F-ECG are achieved through selective separation of the SV-decomposed components. The unique feature of the method is that only one composite maternal ECG signal is required to determine the P-ECG component. The method is numerically robust and computationally efficient     

基于NIR-AOTF的超声换能器阻抗特性分析及驱动系统设计

该文从压电超声换能器的阻抗特性出发,在对换能器的输入阻抗及匹配网络进行了深入研究的基础上设计了一种基于高速单片机和直接数字频率合成器(DDS)的NIR-AOTF驱动系统,采用软件查表法将各个频段驱动信号所对应的电压幅值控制字做成表并保存在单片机中,实现了DDS在各个频段的恒功率输出,并采用新型的宽带阻抗变换网络加载在压电换能器,最终在30~80MHz带宽范围内匹配网络 ＞-0.276dB,回波损耗 ＜-10.173dB。由于驱动电路提供功率为36dBm,实验证明换能器获得功率高于35dBm,达到超声换能器实际工作的3-4W功率要求, NIR-AOTF的0级光谱衍射效率最高达73％。     

基于最小二乘支持向量机的胎儿心电信号提取

该文针对胎儿心电信号难以提取的问题,提出一种从母体腹壁混合信号中提取胎儿心电信号的方法。首先利用最小二乘支持向量机(LSSVM)拟合母体心电信号传导至腹壁所经历的非线性变换,然后将母体心电信号经由所拟合的非线性变换得到腹壁混合信号中的母体心电成分的最优估计,再从腹壁混合信号中减去母体心电成分的最优估计得到含噪声的胎儿心电信号,最后通过经验模式分解(EMD)抑制胎儿心电信号中的基线漂移和噪声,得到清晰的胎儿心电信号。在胎儿心电信号和母体心电信号QRS波完全重叠的情况下,通过该方法能够提取出清晰的胎儿心电信号。实验结果验证了该方法的有效性。     

Intermittent Drug Administration During Labor and Protection of the Fetus

This note describes a method designed to allow drugging of the mother during labor without the child's being significantly affected. The method takes advantage of intervals in each contraction during which the maternal and fetal bloodstreams are unconnected, and in the present is implemented with the aid of a simple electronic unit that uses the signal supplied by a uterine activity transducer to control an injection pump. The results obtained in some sample cases are presented.     

Real-time signal processing for fetal heart rate monitoring

An algorithm based on digital filtering, adaptive thresholding, statistical properties in the time domain, and differencing of local maxima and minima has been developed for the simultaneous measurement of the fetal and maternal heart rates from the maternal abdominal electrocardiogram during pregnancy and labor for ambulatory monitoring. A microcontroller-based system has been used to implement the algorithm in real-time. A Doppler ultrasound fetal monitor was used for statistical comparison on five volunteers with low risk pregnancies, between 35 and 40 weeks of gestation. Results showed an average percent root mean square difference of 5.32% and linear correlation coefficient from 0.84 to 0.93. The fetal heart rate curves remained inside a +/- 5-beats-per-minute limit relative to the reference ultrasound method for 84.1% of the time.     

A new method for measuring small local vibrations in the heartusing ultrasound

In order to diagnose ventricular dysfunction based on the acoustic characteristics of the heart muscle of the ventricle, it is necessary to detect vibration signals from various parts of the ventricular wall. This is, however, difficult using previously proposed ultrasonic diagnostic methods or systems. The reason is that the amplitude of the cardiac motion is large during one beat period which produces large fluctuations in the transit time required for ultrasonic waves to travel from the transducer to the heart and back. This paper proposes a new method for overcoming this problem and accurately measuring small vibrations of the ventricle wall using ultrasound. In this method, the demodulated ultrasound signal reflected at the heart wall is converted from analogue to digital (A/D) signal at a high sampling frequency; from the resultant digital signal, the velocity of the wall is accurately obtained over a wide dynamic range based on the Doppler effect. The proposed method is preliminarily applied to the detection of small vibrations on the aortic wall and the interventricular septum. The new method offers potential for research in acoustical diagnosis of heart and artery dysfunction     

Real-time fetal heart monitoring in biomagnetic measurements using adaptive real-time ICA

Electrophysiological signals of the developing fetal brain and heart can be investigated by fetal magnetoencephalography (fMEG). During such investigations, the fetal heart activity and that of the mother should be monitored continuously to provide an important indication of current well-being. Due to physical constraints of an fMEG system, it is not possible to use clinically established heart monitors for this purpose. Considering this constraint, we developed a real-time heart monitoring system for biomagnetic measurements and showed its reliability and applicability in research and for clinical examinations. The developed system consists of real-time access to fMEG data, an algorithm based on Independent Component Analysis (ICA), and a graphical user interface (GUI). The algorithm extracts the current fetal and maternal heart signal from a noisy and artifact-contaminated data stream in real-time and is able to adapt automatically to continuously varying environmental parameters. This algorithm has been named Adaptive Real-time ICA (ARICA) and is applicable to real-time artifact removal as well as to related blind signal separation problems.