Study On The Detection Electrode Of Electrohysterogram Signal

Electrohysterogram(EHG)is used to represent the electrical activity triggering the mechanical contraction of the myometrium,which plays an important role in detecting uterine contractions,predicting premature births and improving the outcome of perinatal births.It is one of the main expected methods to diagnose preterm labor by collecting the EHG signal of pregnant women.It has been shown that using Laplacian electrodes to record the bio-signals could achieve better spatial resolution and local sensitivity than conventional electrodes.However,its performance of recording uterine contraction activity has not been well investigated.Therefore,this study aimed to compare the performance of different Laplacian electrodes(bipolar,quasi-bipolar,and tri-polar concentric ring electrode)for acquiring uterine contraction activity by computer simulation,saltwater tank experiments and human experiments.At first,a cylinder model and a hemisphere model were developed to simulate the abdomen of a woman by the COMSOL software.Three types of concentric ring electrodes(bipolar,quasi-bipolar and tri-polar)were developed to assess their accuracy,local sensitivity,and consistency.Furthermore,the effects of fat and muscle thickness on potential attenuation were evaluated using the tri-polar electrode with different radius.The results showed that the relative error of tri-polar electrode was significantly smaller than the other electrodes(both p<0.001).Compared to the quasi-bipolar electrode,the bipolar and tri-polar electrodes had larger Laplacian potential attenuation,and the four types of electrodes detected the simulated EHG signals with consistency.In addition,ANOVA analysis showed that,for all the electrodes with different outer ring radius,the effects of fat and muscle thickness on potential attenuation were significant(all p < 0.01).It is therefore concluded that,compared with other electrodes,the tri-polar electrodes had better performance to detect EHG effectively.Second,the saltwater tank experiments were conducted to verify the result of computer simulation.The local sensitivity of three Laplacian electrodes were evaluated by calculating the attenuation of Laplacian potentials in the dipole and dipole band experiments.Besides,the results were compared with the results of the simulation of electrode sensitivity.The results showed that,both in the dipole experiments and the dipole band experiments,the bipolar and tri-polar electrodes had greater attenuations than the others,indicating that they had relatively better local sensitivity.Finally,the flexible tri-polar concentric ring electrode was made in order to evaluate the result of recording EHG signal.The flexible tri-polar concentric ring electrodes and the bluesensor electrode were applied to record the real EHG signals on the abdomen of pregnant women.Then,the root mean square(RMS),sample entropy,power spectrum and signal-to-noise ratio(SNR)of EHG signals were evaluated.In human experiments,the RMS of contraction signals recorded by three electrodes(flexible tri-polar concentric ring electrode,bluesensor electrode,disc electrode)were larger than the non-contraction signals,and the sample entropy of the flexible tri-polar electrode and the bluesensor electrode were significantly smaller than non-contraction signals(p<0.05).Besides,the energy distribution of EHG signals collected by three electrodes were consistent in different frequency bands(p>0.05),and the energy of EHG signals were all concentrated in 0.1-0.34 Hz.The flexible tri-polar electrode and the bluesensor electrode had better SNR than the disc electrode.These findings suggested that the characteristics of EHG signal collected by the flexible tri-polar electrode were similar to the EHG signal collected by the bluesensor electrode,and the EHG signal collected by the flexible tri-polar electrode had concentrated energy and better SNR,which can effectively monitor the uterine activity of pregnant women.According to the above research,the measurement of EHG signals using the tripolar Laplacian electrode could achieve higher accuracy,better local sensitivity.Besides,the distribution of the energy for the EHG signals was concentrated and the EHG signals had better SNR.Therefore,it is concluded that the tri-polar concentric ring electrode can detect uterine contraction activity more effectively and provide more accurate information for preterm birth prevention.