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1

Evaluating the fetal heart rate baseline estimation algorithms by their influence on detection of clinically important patterns

Jezewski J., Horoba K., Roj D., Wrobel J., Kupka T., Matonia A.

Biocybernetics and Biomedical Engineering

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2016

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Vol. 36, no. 4

562--573

EN

A correctly estimated component of fetal heart rate signal (FHR) – so called baseline – is a precondition for proper recognition of acceleration and deceleration patterns. A number of various algorithms for estimating the FHR baseline was proposed so far. However, there is no reference standard enabling their objective evaluation, and thus no methodology of comparing the different algorithms still exists. In this paper we propose a method for evaluation of automatically determined baseline in reference to a set of experts, based on ten separate groups of signals comprising typical variability patterns observed in the fetal heart rate. As it was proposed earlier [1], the given algorithm is evaluated based on the characteristic patterns detected using the obtained baseline, instead of direct analysis of the baseline shape. For the purpose of quantitative assessment of the estimated baseline a new synthetic inconsistency coefficient was applied. The proposed methodology enabled to evaluate eleven well-known algorithms. We believe that the method will be a valuable tool for assessment of the existing algorithms, as well as for developing the new ones.

2

Automated detection of uterine contractions in tocography signals – Comparison of algorithms

Horoba K., Wrobel J., Jezewski J., Kupka T., Roj D., Jezewski M.

Biocybernetics and Biomedical Engineering

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2016

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Vol. 36, no. 4

610--618

EN

Monitoring of uterine contractile activity enables to control the progress of labor. Automated detection of contractions is an integral part of the signal analysis implemented in computer- aided fetal surveillance system. Comparison of four algorithms for automated detection of uterine contractions in the signal of uterine mechanical activity is presented. Three algorithms are based generally on analysis of the frequency distribution of signal values. The fourth method relies on analyzing the rate of changes of the uterine activity signal. The reference data in form of beginning and end of contraction episodes were provided by human experts. Obtained results show that all algorithms were capable to detect above 91% reference contractions, and less than 7% of recognized patterns were false. Two algorithms can be distinguished as providing a higher performance expressed by the sensitivity of 95% and the positive predictive value of 97%. Such results could be obtained by optimization of contraction validation criteria.

3

Efficiency of automated detection of uterine contraction using tocography

Horoba K., Wrobel J., Jezewski J., Kupka T., Czabanski R., Roj D., Jezewski M.

Journal of Medical Informatics & Technologies

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2015

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Vol. 24

207--214

EN

Monitoring of uterine contractile activity enables to control the progress of labour. Automated detection of contractions is to be an integral part of the signal analysis implemented in computer aided fetal surveillance system. Evaluation of efficiency of three algorithms for automated detection of uterine contractions in the signal of uterine mechanical activity is presented. These algorithms are based generally on analysis of the frequency distribution of signal values. The reference data in form of beginning and end of contraction episodes were obtained from human expert. Obtained results showed high efficiency of the algorithms tested where the best one ensured the sensitivity and positive predictive value equal to 92.2 and 97.2, respectively.

4

A novel approach to comparison of the fetal heart rate baseline estimation algorithms

Jezewski J., Horoba K., Roj D., Wrobel J., Kupka T., Matonia A.

Journal of Medical Informatics & Technologies

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2015

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Vol. 24

231--238

EN

A number of algorithms for estimating the so called fetal heart rate baseline was proposed so far. However, there is no reference pattern enabling their objective evaluation, and thus no methodology of comparing the competing algorithms still exists. In this paper we propose a method for evaluation of automatically determined baseline in reference to a group of experts, basing on ten separate groups of signals comprising typical patterns observed in the fetal heart rate. For the purpose of quantitative assessment of the estimated baseline a new synthetic inconsistency coefficient is presented. The proposed methodology was applied to evaluate ten well-known algorithms. We believe that the method will be a valuable tool for assessment of the existing algorithms, as well as for developing new ones.

5

The influence of signal loss episodes on fetal heart rate variability measures

Wróbel J., Roj D., Jeżewski J., Horoba K., Kupka T., Jeżewski M.

Journal of Medical Informatics & Technologies

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2014

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Vol. 23

35--42

EN

The most important features indicating appropriate fetal development are the measures of instantaneous variability of a fetal heart rate (FHR), describing fluctuations of the beat-to-beat heart intervals. The most popular method for the FHR acquisition is the Doppler ultrasound technique. However, it is very sensitive to various motion artifacts distorting the signal being acquired. The aim of our work was to evaluate the influence of signal loss episodes on the parameters quantitatively describing the instantaneous variability of the FHR. For this purpose we artificially inserted signal loss episodes to the recordings, in different patterns and percentage, in accordance with the real characteristics of the signal loss segments. We particularly would like to answer the question if the signals with significant amount of signal loss can be reliably evaluated by means of instantaneous variability measures, and which of these measures (numerical indices) are more robust to the missing values.

6

Automated detection of fetal movements in Doppler ultrasound signals versus maternal perception

Wróbel J., Kupka T., Horoba K., Matonia A., Roj D., Jeżewski J.

Journal of Medical Informatics & Technologies

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2014

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Vol. 23

43--50

EN

Analysis of movement activity is important since it enables detection of nonreactive fetal heart rate recordings. The aim of the study was to develop an algorithm for automated detection of the fetal movement activity (actogram), based on analysis of the Doppler ultrasound signal, and to evaluate a reliability of the actogram as a source of information about the fetal movements. Bandpass filtering (20-80 Hz) was used to separate the actogram signal describing the fetal movement activity. Simultaneously there were recorded the markers of fetal movements perceived by mother, being the reference information. For the determination of the binary actogram, the authors proposed an algorithm in which the classification threshold was estimated at the beginning of each recording and was adaptively modified during its duration. The algorithm ensured detection of up to 89% of movement episodes corresponding to movements perceived by mother. At the same time almost as high number of episodes not related to the reference information was recognized. Obtained results revealed that the automated analysis of fetal movements is characterized by much higher sensitivity of movement episode detection compared to the maternal perception.

7

Reconstruction of FHR series recorded via ultrasound - method validation using abdominal fetal electrocardiography

Kupka T., Horoba K., Roj D., Matonia A., Czabanski R., Jezewski M.

Journal of Medical Informatics & Technologies

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2013

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Vol. 22

135--141

EN

Analysis of variability of the fetal heart rate (FHR) is very important for fetal wellbeing assessment. The beat-to-beat variability is described quantitatively by the indices originated from invasive fetal electrocardiography which provides the FHR signal in a form of time event series. Nowadays, monitoring instrumentation is based on Doppler ultrasound technology. The fetal monitors provide the output signal in a form of evenly spaced measurements. The goal of this work is to present a new method for the FHR signal processing, which enables extraction of time series of consecutive heartbeat intervals from the evenly repeated values. The proposed correction algorithm enables recognition and removal of the duplicated measurements. Reliable evaluation of the algorithm requires the reference event series, thus the FHR signals were obtained from abdominal fetal electrocardiograms to be used in this research study.

8

A routing protocol for wireless network of bedside monitors in fetal surveillance system

Seredynski R., Horoba K., Roj D., Bernys M., Przybyla T., Jezewski J.

Journal of Medical Informatics & Technologies

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2012

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Vol. 21

27--33

EN

The paper presents the methodology of wireless network design, developed according to the requirements originating from existing wired fetal surveillance systems. The proposed network structure is based on popular radio frequency modules, operating in 433/866MHz band. The described solution is a simple and cost effective alternative to the wired networks, and it will vastly increase the mobility of fetal monitors. The authors also describe software tools which were designed for this purpose and the results of simulations performed on their basis.

9

Fuzzy prediction of fetal acidemia

Czabański R., Roj D., Jeżewski J., Horoba K., Jeżewski M.

Journal of Medical Informatics & Technologies

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2011

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Vol. 17

81--87

EN

Cardiotocography is the primary method for biophysical assessment of a fetal state. It is based mainly on the recording and analysis of fetal heart rate signal (FHR). Computer systems for fetal monitoring provide a quantitative description of FHR signals, however the effective methods for their qualitative assessment are still needed. The measurements of hydronium ions concentration (pH) in newborn cord blood is considered as the objective indicator of the fetal state. Improper pH level is a symptom of acidemia being the result of fetal hypoxia. The paper proposes a twostep analysis of signals allowing for effective prediction of the acidemia risk. The first step consists in the fuzzy classification of FHR signals. The task of fuzzy inference is to indicate signals that according to the FIGO guidelines represent the fetal wellbeing. These recordings are eliminated from the further classification with Lagrangian Support Vector Machines. The proposed procedure was evaluated using data collected with computerized fetal surveillance system. The classification results confirmed the high quality of the proposed fuzzy method of fetal state evaluation.

10

Application of generalized filters for estimation of fetal heart rate baseline

Pander T., Przybyla T., Wrobel J., Jezewski J., Roj D.

Journal of Medical Informatics & Technologies

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2011

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Vol. 17

73--79

EN

This paper addresses the problem of impulsive noise cancellation in digital signal area. The myriad and meridian filters are the type of robust filters which are very useful in suppressing the impulsive type of noise. The cost functions of theses filters have very similar structure. In this paper the generalized filter based on Lp norm is presented. The proposed filter operates in a wide range of impulsive noise due to the proper adjustment of p in the Lp norm. The presented filter is applied to suppress an impulsive noise in fetal heart rate (FHR) signal. Simulation results confirm the validity of the proposed filter.

11

Improving the periodicity measurement in fetal heart activity signal

Roj D., Wróbel J., Horoba K., Przybyła T., Kupka T.

Journal of Medical Informatics & Technologies

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2010

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Vol. 16

19--26

EN

In this paper we discussed the influence of preliminary processing of the ultrasound Doppler signal on accuracy of the fetal heart rate estimation as well as on reliability of the FHR instantaneous variability assessment. We attempted to develop an optimal processing channel of US Doppler signal in order to measure the periodicity of fetal heart activity with accuracy as close as possible to that ensured by FECG. The FHR values determined from the US signal were compared to the reference data obtained from direct FECG. In a final evaluation we used the parameters describing the FHR variability as the clinically important signal features being the most sensitive to any periodicity inaccuracy. The results proved that an application of proposed algorithms improves the accuracy of interval measurements and FHR instantaneous variability assessment in relation to the new-generation fetal monitors.

12

Generalized fuzzy clustering method

Przybyła T., Roj D., Jeżewski J., Matonia A.

Journal of Medical Informatics & Technologies

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2010

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Vol. 16

69--76

EN

This paper presents a new hybrid fuzzy clustering method. In the proposed method, cluster prototypes are values that minimize the introduced generalized cost function. The proposed method can be considered as a generalization of fuzzy c–means (FCM) method as well as the fuzzy c–median (FCMed) clustering method. The generalization of the cluster cost function is made by applying the Lp norm. The values that minimize the proposed cost function have been chosen as the group prototypes. The weighted myriad is the special case of the group prototype, when the Lp norm is the L2 (Euclidean) norm. The cluster prototypes are the weighted meridians for the L1 norm. Artificial data set is used to demonstrate the performance of proposed method.

13

Evaluation of predictive capabilities of quantitative cardiotocographic signal features

Czabański R., Jeżewski M., Roj D., Szaszkowski Z., Kupka T., Wróbel J.

Journal of Medical Informatics & Technologies

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2010

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Vol. 16

11--17

EN

Cardiotocography (CTG) is the main method of assessment of the fetal state during pregnancy and labour used in clinical practice. It is based on quantitative analysis of fetal heart rate, fetal movements and uterine contractions signals. The evaluation of the CTG signals can be made using criteria recommended by International Federation of Obstetrics and Gynecology. Nevertheless, the diagnosis verification is possible only after the delivery on the basis of newborn assessment. In the proposed work we evaluated the capacity of quantitative analysis of CTG traces in predicting fetal outcome. The relationship between CTG signal features and attributes of fetal outcome was assessed on the basis of ROC curves analysis. The obtained results indicate the adequate predictive capabilities of the selected CTG features especially for fetal outcome assessed with Apgar score and suggest the necessity of applying the criteria for the CTG traces evaluation that are related to the gestational age. Our study also shows the value of the CTG monitoring as a screening procedure providing appropriate confirmation of fetal wellbeing.

14

Unsupervised clustering for fetal state assessment based on selected features of the cardiotocographic signals

Przybyła T., Jeżewski J., Roj D.

Journal of Medical Informatics & Technologies

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2009

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Vol. 13

157--162

EN

In modern obstetrics the cardiotocography is a routine method of fetal condition assessment based mainly on analysis of the fetal heart rate signals. The correct interpretation of recorded traces from a bedside monitor is very difficult even for experienced clinicians. Therefore, computerized fetal monitoring systems are used to yield the quantitative description of the signal. However, the effective techniques enabling automated conclusion generation based on cardiotocograms are still being searched. The paper presents an attempt to diagnose the fetal state basing on seventeen features describing the cardiotocographic records. The proposed method applies the unsupervised classification of signals. During our research we tried to classify the fetal state using the fuzzy c-means (FCM) clustering. We also tested how the efficiency of classification could be influenced by application of principal component analysis (PCA) algorithm. The obtained results showed that unsupervised classification cannot be considered as a support to fetal state assessment.

15

Modification of obstetrical surveillance systems for effective patient management and home-care of at-risk pregnancy

Roj D., Wróbel J., Horoba K, Kotas M., Przybyła T.

Journal of Medical Informatics & Technologies

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2009

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Vol. 13

201--206

EN

The paper presents some aspects of telemedical fetal monitoring where the biomedical signals are acquired remotely at patient’s home and wirelessly transmitted to the central computer through the GSM network and Internet. Signals are acquired during the monitoring sessions, and along with analysis results, they create uniform data structure describing the medical history of patient since the first monitoring to the labour. The proposed structure of database was based on the currently used in centralized monitoring systems, and extended by information essential for remote monitoring purposes. Internet-based telemedical systems allow for remote access to collected data, however, it is necessary to secure the database against unauthorized access to patient’s personal data and medical history. The proposed structure of database records allows for easy searching and viewing of patient data forms and monitoring traces. These features cause that the database constitutes valuable research material, which enables to relate parameters of particular monitoring records, acquired during pregnancy, to the real fetal outcome.

16

Wybrane aspekty rejestracji mechanicznej aktywności serca płodu, a dokładność pomiaru zmienności rytmu

Roj D., Wróbel J., Jeżewski J., Kotas M., Przybyła T.

Aktualne Problemy Biomechaniki

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2009

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z. 3

201--206

PL

Podstawową metodą rejestracji rytmu pracy serca płodu jest monitorowanie mechanicznej czynności serca, na podstawie analizy efektu przesunięcia dopplerowskiego wiązki ultradźwiękowej, odbitej od poruszających się zastawek. Złożony kształt sygnału, obejmującego liczne zdarzenia ruchowe w ramach jednego cyklu serca, sprawia, że pomiar okresowości może być obarczony błędem. W pracy omówiono wpływ położenia przetwornika ultradźwiękowego na dokładność pomiaru rytmu serca oraz możliwość poprawy precyzji przez analizę sygnału dopplerowskiego w ograniczonych pasmach.

EN

Commonly used method of fetal heart rate acquisition is based on monitoring of mechanical activity of fetal heart, using the Doppler effect in ultrasound wave reflected from the heart valves. The complex form of signal, containing several valve movements in a single heart cycle, results in high value of interval measurement error. We investigated the influence of transducer placement on precision of fetal heart rate determination and the possibility of accuracy improvement by limitation of signal bandwidth.

17

The influence of window size of autocorrelation function on fetal heart rate variability measurement using the Doppler ultrasound signal

Roj D., Fuchs T., Przybyła T., Jeżewski M., Matonia A., Gacek A.

Journal of Medical Informatics & Technologies

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2008

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Vol. 12

111--116

EN

Commonly used noninvasive fetal monitoring is based on fetal heart rate (FHR) variability analysis of the Doppler ultrasound signal coming from the mechanical activity of the fetal heart. Estimation of periodicity of acquired signals using the autocorrelation technique is very important. The determination of cardiac intervals using the Doppler signal is more difficult than in electrocardiography, where the R-waves are evident. We investigated the influence of the autocorrelation window size on the FHR variability analysis. The indices describing the FHR variability calculated for signals obtained using two different autocorrelation techniques with various window lengths were compared with the reference ones obtained from fetal electrocardiogram. The optimal window was a compromise between artifacts resistance and the averaging level of instantaneous variability.

18

Telemedical system for home fetal monitoring with online analysis of bioelectricalabdominal signals

Wróbel J., Jeżewski J., Matonia A., Kupka T., Gacek A., Roj D.

Journal of Medical Informatics & Technologies

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2008

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Vol. 12

91--95

EN

This paper presents some aspects of the on-line remote fetal monitoring system based on the GPRS data transmission service and WAN network. The remote signal recording instrumentation consists of bioelectrical signal recorder and tablet PC computer. The central surveillance system located in hospital has a capability of simultaneous monitoring of up to 24 patients, both remotely and within hospital. The system enables analysis, dynamic presentation and archiving of signals and medical data. The clinical interpretation is immediately available in hospital as well as at patient's home or attending doctor office.