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Compact UWB Antenna Design for Stroke Diagnosis

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Compact UWB Antenna Design for Stroke Diagnosis Improving landfill monitoring programs withFeasibility the aid of of geoelectrical fetal EEG - Recordingimaging techniques and geographical information systems Master’sduring labor Thesis by usingin the STANMaster S31 Degree Programme, Civil Engineering KEVINFarhad ABTAHI HINE Supervisor: Professor Kaj Lindecrantz Department of Civil and Environmental Engineering DivisionCo-Supervisor: of GeoEngineering Dr. Nils Lofgren Engineering Geology Research Group CHALMERSExaminer: Professor UNIVERSITY Bo Håkansson OF TECHNOLOGY Göteborg, Sweden 2005 Master’sDepartment Thesis of Signal 2005:22 and System CHALMERS UNIVERSITY OF TECHNOLOGY Gothenburg, Sweden 2011 Master’s Thesis EX101/2011 Feasibility of fetal EEG recording during labor by using STAN S31 c Farhad Abtahi, 2011 Master’s Thesis EX101/2011 Department of Signal and System Chalmers University of Technology SE-41296 Göteborg Sweden Tel. +46-(0)31 772 1000 Prepared With LATEX Reproservice / Department of Signal and System Göteborg, Sweden 2011 Abstract Fetal electrocardiography is currently used for monitoring of fetus during labor. ST-Analysis is done by monitoring amplitude of T wave to find elevation of ST wave amplitude which is a sign of hypoxia. The ST-Analysis in combination of standard cardiotocography (CTG) helps finding general ischemia due to specific fetal positioning that chokes the umbilical cord. The fetal electrocardiogram signals obtain by placing electrode on fetal scalp during labor (after water breaks) referred to an electrode on the mother’s thigh. The STAN S31 is an apparatus which is use for intra-partum fetal monitoring. This method is currently used with great success in majority of Swedish hospitals and in 80 to 90 percent of labor and delivery clinics in Norway, Belgium and Denmark. The purpose of this project is to study feasibility of extracting brain waves from recording signals. The fetal EEG could be used to improve monitoring in cases were the fetus is too exhausted to respond with T amplitude elevation or when monitoring is started too late and hence T amplitude elevation has already occurred and relative measures are useless. During this study, amplifier modifications were done to achieve 1 mV resolution. The modified STAN device is used for recording in the delivery department of Sahlgrenska University Hospital, Mölndal. Two ECG elimination methods are implemented; ensemble average subtraction and wavelet denoising methods. Comparison of these methods has been done by use of simulated and real signals. The result shows successfully elimination of ECG artifacts. However, by using the ensemble average subtraction method some attenuated QRS are still visible. It is also concluded that ensemble average subtraction behaves like a high-pass filter while wavelet denoising method acts as low-pass filter. The preference of each method depends on the application. The remained signals after eliminating ECG have time and frequency patterns similar to EEG. How- ever, the lack of sufficient eventful recordings and limits in frequency range of high resolution channel makes the final decision about existence of EEG signals impossible. The final judgment needs future investigation to improve the frequency range of the signals and to correlate the potential EEG signals to somatosensory evoked potentials or other events. Keywords: Fetal Monitoring, Fetal ECG, Fetal EEG, EEG Noise Reduction, Wavelet Denoising, En- semble Average Subtraction, STAN S31 Acknowledgments I am very grateful for the help and support of my supervisor, Professor Kaj Lindecrantz. Also special thanks to my co-supervisor Dr. Nils Löfgren, who always was available for project with his valuable time. This work have not been possible without help of associate Professor. Magnus Thordstein who did visual analysis of signals and pushed the project. The big thanks to Dr. Johan Lofhede who share his place with me. Finally, I would also like to thank Shirin for her love and patience with me. I am also very grateful to my family for their long-distance support. Farhad Abtahi, Göteborg 2011 Contents Abstract ii Acknowledgments iv Contents vi Figures viii Tables x 1 Introduction 1 1.1 Objective...............................................2 1.2 Outline................................................3 2 Background 4 2.1 Cardiovascular system.......................................4 2.1.1 Heart Activities.......................................4 2.1.2 Fetal vs. Adult Heart....................................5 2.1.3 Electrocardiogram.....................................5 2.2 Human Brain............................................7 2.2.1 Electroencephalogram...................................7 2.2.2 Fetal Electroencephalogram................................8 2.3 Wavelets............................................... 10 2.3.1 Introduction......................................... 10 2.3.2 Wavelet transform..................................... 10 2.3.3 Wavelets properties..................................... 11 2.3.4 Wavelets families...................................... 12 3 Experimental Setup 14 3.1 Hardware Modification and Available Channels........................ 14 3.2 Frequency Challenges....................................... 15 3.3 Recording Protocol......................................... 15 4 Methods 17 4.1 Preprocessing............................................ 18 4.2 Ensemble Average Subtraction Method............................. 18 4.2.1 QRS and Heartrate Detection............................... 19 4.3 Wavelets Noise Rejection Method................................. 22 4.4 Comparison of methods with simulated signals........................ 24 4.5 Visual Analysis........................................... 25 vi CONTENTS 5 Results 26 5.1 Recorded signals.......................................... 26 5.2 Ensemble Averaging Subtraction Method............................ 26 5.3 Wavelet Denoising Method.................................... 26 5.4 Comparison of Methods...................................... 26 5.4.1 Simulated Signals...................................... 26 5.4.2 Real Signals......................................... 28 5.5 Visual Analysis........................................... 28 6 Discussion 31 7 Conclusion 33 8 Future Work 34 References 36 Appendix A-i A Appendix A-i A.1 Appendix1-Registration Form................................... A-ii A.2 Appendix2-Digital Comb Filter.................................. A-iii vii List of Figures 1.1 The major medias which influence the fetal cardiac surface potentials [1]..........1 1.2 STAN S31 and it’s usage in hospital...............................2 2.1 The Conducting system of the heart...............................5 2.2 The waveform of typical ECG which can record by using skin surface............6 2.3 The ECG waves compare to the heart electrical activities...................6 2.4 Different parts of brain and cerebrum...............................7 2.5 The structure and electric dipole of pyramidal cells.......................8 2.6 The Brainwaves in delta, theta, alpha and beta bands......................9 2.7 The comparison of Time-frequency resolution of windowed Fourier transform and wavelet transform............................................... 11 2.8 The procedure of fast wavelet transform and structure of the transformed signal...... 11 2.9 The wavelet kernel function of Coiflet-1, db-2, symm-8 and rbior-4.4............ 13 3.1 The Goldtrace ECG scalp electrode, placement of scalp electrode and mother thigh skin electrode................................................ 14 3.2 Schematic Diagram of Non-inverting amplifier......................... 15 3.3 Schematic Diagram of ECG Amplifier.............................. 16 4.1 Magnitude response of used Comb Filter for removing power line interference...... 18 4.2 Procedure of ensemble averaging method, R-Peak detection, synchronous partitioning, averaging and subtraction..................................... 19 4.3 Procedure of QRS detection..................................... 19 4.4 QRS detection; Raw signal vs. Band-passed signal........................ 20 4.5 QRS detection;the differentiated and squared signal...................... 20 4.6 QRS detection;the integrated signal over ECG signal and detected QRS boundaries.... 21 4.7 The ECG signal and detected R-peaks, Q-points and S-points................. 22 4.8 Wavelet noise rejection steps.................................... 22 4.9 Decomposition of 10 second recorded signal from fetus head by using Coiflet-1...... 23 4.10 The Simulated EEG signal contaminated by ECG....................... 24 4.11 Screenshot of EDFbrowser..................................... 25 5.1 The ECG elimination by using Ensemble Average Subtraction Denoising method...... 27 5.2 The ECG elimination by using Wavelet Denoising method.................. 27 5.3 The reconstructed signals by using Wavelet Toolbox thresholding compare to modified thresholding............................................. 29 5.4 The ECG elimination of simulated signal with Ensemble Average Subtraction and Wavelet Denoising methods.......................................... 29 5.5 Comparison of Ensemble Average Subtraction and Wavelet Denoising methods with sim- ulated signal............................................. 30 viii LIST OF FIGURES 5.6 Comparison of Ensemble Average Subtraction and Wavelet Denoising methods with real signal................................................. 30 ix List of Tables 2.1 ECG waves and intervals......................................5 2.2 Different part of cerebrum.....................................7
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