Multi-scale sample entropy and recurrence plots distinguish healthy from suffering foetus

International audienceCurrently, the assessment of the state of fetal well-being using ultrasound is a challenge in the obstetrical world. To assess the fetal well-being, parameters are derived from the fetal heart rate and fetal movements. We estimated the fetal heart rate using a multi-sensor, multi-gate pulsed Doppler system and we propose to study the complexity of heart rate by calculating the multi-scale entropy and the parameters deduced from the recurrence plots. The article presents a preliminary study that evaluates the relevance of complexity parameters in assessing the state of fetal well-being. Our results show that complexity parameters can distinguish healthy from suffering foetus

Similarity Quantification Analysis to Detect Suffering Fetus

International audienceTo characterize a dynamical system, a number of descriptors or invariants can be used. Here we proposed to review and generalize the analysis of recurrence by introducing the con-cept of similarity. In this study, we showed that it was possible to distinguish the fetal heart rate of healthy from suffering fe-tus using the similarities of a time series, while the analysis of recurrence does not allowed it

Estimation du rythme cardiaque fœtal par l'estimateur YIN

International audienceTechniques dedicated to the fetal heart rate detection identify the patterns that repeat themselves over the time. The heart rate estimation is algorithmically similar to the estimation of the fundamental frequency (pitch) of voice signals. The new YIN technique introduced for the estimation of the fundamental frequency is applied to fetal heart rate estimation from the directional Doppler signals. We compare the performances in terms of probability of detection and accuracy of the estimation of the technique YIN with those of the cross-correlation, implemented in the Oxford SONICAID™ monitors. A better detection probability and accuracy of estimation of fetal heart rate was obtained in case of YIN.Les techniques dédiées à la détection du rythme cardiaque fœtal (RCF) identifient des motifs du signal qui se répètent dans le temps. Algorithmiquement, l’estimation du rythme cardiaque est similaire à l’estimation de la fréquence fondamentale des signaux de parole. Nous proposons ici de comparer la technique existante basée sur la corrélation-croisée à la nouvelle technique YIN pour l’estimation du RCF à partir des signaux Doppler directionnels. Nous avons comparé les performances en termes de probabilité de détection et de précision d’estimation de la technique YIN avec celles de la corrélation-croisée, implémentée dans les moniteurs Oxford SONICAID™. Une meilleure probabilité de détection et une meilleure précision d’estimation du RCF a été obtenue dans le cas de la technique YIN

Amélioration de l'estimation du rythme cardiaque foetal en utilisant les signaux Doppler directionnels et YIN

National audienceTechniques dedicated to the fetal heart rate detection identify the patterns that repeat themselves over the time. The heart rate estimation is algorithmically similar to the estimation of the fundamental frequency (pitch) of voice signals. The new YIN technique introduced for the estimation of the fundamental frequency is applied to fetal heart rate estimation from the directional Doppler signals. We compare the performance of YIN with those of cross-correlation, which is implemented in the Oxford SONICAID monitors. A better detection probability of fetal heart rate was obtained in case of YIN.Les techniques dédiées à la détection du rythme cardiaque fœtal (RCF) identifient des motifs du signal qui se répètent dans le temps. Algorithmiquement, l'estimation du rythme cardiaque est similaire à l'estimation de la fréquence fondamentale des signaux de parole. Nous proposons ici de comparer la technique existante basée sur la corrélation-croisée à la nouvelle technique YIN pour l'estimation du RCF à partir des signaux Doppler directionnels. Nous avons comparé les performances en termes de probabilité de détection et de précision d'estimation de la technique YIN avec celles de la corrélation-croisée, implémentée dans les moniteurs Oxford SONICAID™. Une meilleure probabilité de détection et une meilleure précision d'estimation du RCF a été obtenue dans le cas de la technique YIN

Multi-scale similarity entropy as a complexity descriptor to discriminate healthy to distress foetus

International audienceThis paper deals with the discrimination between suffering foetuses and normal foetuses by means of a multi-scale similarity entropy. Sample entropy and similarity entropy are evaluated in multi-scale analysis on foetal heart rate signals. Without multi-scale analysis, our results show that only the similarity entropy differentiate suffering foetuses to normal foetuses. Furthermore with the multi-scale analysis, our results show that both the sample entropy and the similarity entropy can discriminate the distressed foetuses to normal foetuses. In all cases the similarity entropy outperforms the sample entropy that is encouraging for another biomedical applications

Optimization of the Contrast Tissue Ratio in Ultrasound Contrast Imaging by an Adaptive Transmit Frequency

Conventionnal ultrasound contrast imaging systems use a fixed transmit frequency. However it is known that the insonified medium (microbubbles) is time-varying and therefore an adapted time-varying excitation is expected. We suggest an adaptive imaging technique which selects the optimal transmit frequency that maximizes the contrast tissue ratio (CTR). The method is proposed with the contrast imaging and the harmonic contrast imaging. Simulations were carried out for encapsulated microbubbles of 2µm-radius by considering the modified Rayleigh-Plesset equation for various pressure levels (80 kPa up to 420kPa). In vitro experiments have been carried out using using a 2.25 MHz transmitter transducer and using a programmable waveform. We show, through experiments, that our adaptive imaging technique increases the CTR of 2 dB compared to the standard method looking at the central frequency. By proposing a close loop system whose frequency adapts itself with the perfused media, throughout the examination, the optimization system adapt itself to the bubble population to seek the best trade-off between the bubble response and the transducer bandwidth

New estimators and guidelines for better use of fetal heart rate estimators with Doppler ultrasound devices

International audienceCharacterizing fetal wellbeing with a Doppler ultrasound device requires computation of a score based on fetal parameters. In order to analyze the parameters derived from the fetal heart rate correctly, an accuracy of 0.25 beats per minute is needed. Simultaneously with the lowest false negative rate and the highest sensitivity, we investigated whether various Doppler techniques ensure this accuracy. We found that the accuracy was ensured if directional Doppler signals and autocorrelation estimation were used. Our best estimator provided sensitivity of 95.5%, corresponding to an improvement of 14% compared to the standard estimator

Optimization of the Contrast Tissue Ratio in Ultrasound Contrast Imaging by an Adaptive Transmit Frequency

Conventionnal ultrasound contrast imaging systems use a fixed transmit frequency. However it is known that the insonified medium (microbubbles) is time-varying and therefore an adapted time-varying excitation is expected. We suggest an adaptive imaging technique which selects the optimal transmit frequency that maximizes the contrast tissue ratio (CTR). The method is proposed with the contrast imaging and the harmonic contrast imaging. Simulations were carried out for encapsulated microbubbles of 2µm-radius by considering the modified Rayleigh-Plesset equation for various pressure levels (80 kPa up to 420kPa). In vitro experiments have been carried out using using a 2.25 MHz transmitter transducer and using a programmable waveform. We show, through experiments, that our adaptive imaging technique increases the CTR of 2 dB compared to the standard method looking at the central frequency. By proposing a close loop system whose frequency adapts itself with the perfused media, throughout the examination, the optimization system adapt itself to the bubble population to seek the best trade-off between the bubble response and the transducer bandwidth

Optimization of Contrast to Tissue Ratio by Frequency Adaptation in Pulse Inversion Imaging

Simulation program available : http://www.runmycode.org/companion/view/1956International audienceContrast imaging has significantly improved clinical diagnosis by increasing the contrast-to-tissue ratio after microbubble injection. Pulse inversion imaging is the most commonly used contrast imaging technique, as it greatly increases the contrast-to-tissue ratio by extracting microbubble nonlinearities. The main purpose of our study was to propose an automatic technique providing the best contrast-to-tissue ratio throughout the experiment. For reasons of simplicity, we proposed to maximize the contrast-to-tissue ratio with an appropriate choice of the transmit frequency. The contrast-to-tissue ratio was maximized by a closed loop system including the pulse inversion technique. An algorithm based on the gradient provided iterative determination of the optimal transmit frequency. The optimization method converged quickly after six iterations. This optimal control method is easy to implement and it optimizes the contrast-to-tissue ratio by selecting the transmit frequency adaptively

Robust estimation of fetal heart rate from US Doppler signals

International audienceIn utero, Monitoring of fetal wellbeing or suffering is today an open challenge, due to the high number of clinicalparameters to be considered. An automatic monitoring of fetal activity, dedicated for quantifying fetal wellbeing, becomes necessary. For this purpose and in a view to supply an alternative for the Manning test, we used an ultrasound multitransducer muligate Doppler system. One important issue (and first step in our investigation) is the accurate estimation of fetal heart rate (FHR). An estimation of the FHR is obtained by evaluating the autocorrelation function of the Doppler signals for ills and healthiness foetus. However, this estimator is not enough robust since about 20% of FHR are not detected in comparison to a reference system. These non detections are principally due to the fact that the Doppler signal generated by the fetal moving is strongly disturbed by the presence of others several Doppler sources (mother' s moving, pseudo breathing, etc.). By modifying the existing method (autocorrelation method) and by proposing new time and frequency estimators used in the audio' s domain, we reduce to 5% the probability of non-detection of the fetal heart rate. These results are really encouraging and they enable us to plan the use of automatic classification techniques in order to discriminate between healthy and in suffering foetus