noise analysis & qrs detection in ecg signals

Base paper: - http://www.ipcsit.com/vol47/027-ICCTS2012-T30009.pdf

Noise Analysis & QRS Detection in ECG Signals

International Proceedings of Computer Science and Information Technology.

Abstract:

With the latest advancements in electronics, several techniques are used for removal of unwanted entities from signals especially that are implied in the most sophisticated applications. The removal of power line interference from most sensitive medical monitoring equipment can also be removed by implementing various useful techniques. The power line interference (50/60 Hz) is the main source of noise in most of bio-electric signals. The thesis report presents the removal of power line interference and other single frequency tones from ECG signal using the advanced adaptive filtering technique with LMS (least mean square) algorithm. The thesis is based on digital signal processing (DSP) techniques with MATLAB package, with the emphases on design of adaptive LMS algorithm. The adaptive interference removal technique can be used for removal of power line interference in various potential applications such as recording Electrocardiograms (ECG), Electroencephalogram (EEG) and Electromyogram (EMG). MATLAB package will be used in the thesis work which is a powerful tool for the interactive design in most of the scientific applications and complex engineering calculations. As an additional in order to achieve the goal of thesis it will also be investigated and implemented for the removal of harmonics (hum) and high frequency noise from ECG signal by using general notch rejection filters, which are partial milestone for the thesis.


A: - Removal of Power Line Interference (50 Hz) from ECG Signal by LMS Algorithm FilterTap = 16 mu = 0.005


FilterTap = 16 mu = 0.009


B: - Removing of Harmonics and High Frequency Noise from Original ECG Signal

Conclusions:

This report is devoted to the problems and solutions on removal of Power Line Interference and other Single Frequency Tones from Signals. The understanding of noise cancellation from ECG signal was explained clearly to the readers, the methods and techniques applicable to be used discussed throughout the report. It has been proposed a solution for the power line interference its respective harmonics and high frequency noise interferences from original ECG signal. The results have been obtained which were required in purpose statement of the report. In general FIR filters are used because these types of filters have simple architecture and are logically stable, so the FIR filter was chosen for the development of the system. The research has been made for the selection of filters and algorithm, two kind of adaptive filters i.e. FIR (Finite impulse response) & IIR (Infinite impulse response) and two kinds of algorithms, the LMS (least mean square) & RLS (recursive least squares) algorithms were studied and examined. The LMS algorithm is the most widely used adaptive filtering algorithm in biomedical monitoring equipment, so it was decided to be employed for the thesis to get the required solution for the main purpose. The applications of the LMS algorithm can be implemented due to its simplicity and robustness. An adaptive filter is used in applications that require different filter characteristics in response to variable signal conditions. The speed of adaptation and accuracy of the noise cancellation after adaptation are important measures of performance for noise cancellation algorithm. The goal of the adaptive filter is to match the filter coefficients to the noise so that the adaptive filter can subtract the noise out from signal. So adaptive filtering technique was selected to achieve the goal of thesis. The test for the simulation of ECG signal has been taken. The signal is corrupted by power line interference of 50 Hz. It is observed that the frequency of the power line interference is 50 Hz which is then mixed with original ECG signal, it is also examined that the mixed signal is displayed on the plot. After passing through LMS algorithm the filtered output is nearly same as the input signal with some acceptable distortion range. The value of step size μ play an important role in determining the convergence speed, stability and residual error after convergence. The convergence rate was controlled


by Removal of Power Line Interference and other Single Frequency Tones from Signals MSc Thesis Report, Mälardalen University, Sweden 56 LMS step size μ. The ECG signal graphs described in the simulation results verify the adaptation of the LMS adaptive algorithm by changing various parameters like step size, convergence value (μ) and filter taps have various effects on the output graphs. The result shows that LMS is an effective algorithm used for the adaptive filter in the noise cancellation implementation. By increasing the filter order it shows a convergence rate but makes the results more precise and by decreasing the step size value it creates the slower convergence but improves the stability and accuracy. The recovered signal closely resembles to the original simulated signal minus the noise. It can be seen that the implementation of the algorithm functions as correctly and efficiently. By comparing the graphs of the input signal of ECG and output signal, it is noticed that the simulation program performs satisfactorily and that noise cancellation from original ECG signal is acquired. The overall performance of LMS algorithm for power line interference is achieved. Furthermore the general notch rejection filters method also performs the correct operation while filtering the noise from original ECG signal. This technique for the investigation, implemented and analysis of removal of harmonics and high frequency noise from original ECG signal performed satisfactory. It is concluded that the low frequency noise (hum) and high frequency noise can be removed from original ECG signal by the implementation of general notch rejection filters method and the desired result can be achieved accurately. Future Enhancements: The depth knowledge achieved is in a number of aspects by using digital signal processing techniques with MATLAB package for medical monitoring equipment (ECG). It provides the real concepts along with the theoretical backgrounds of removal of power line interference, single frequency tones and high frequency noise from original ECG signal. This enhances the understanding and self-confidence in the field of electronics and biomedical engineering. In the thesis, the adaptive signal processing filtering technique based on LMS algorithm could be implemented for more signals and also improvement of the thesis can be further implemented with different algorithms such as NLMS and RLS to achieve the desired results. It could also be investigate and implement the removal of multiple of harmonics from ECG signal. In further research it would be of interest to make a broader study and look at some companies for related project for the implementation. References: [1] Stacy Finlay, Carrie Klekta and Ernie Packulak, Adaptive Noise Cancellation for ECG Signal, 2002 [2] http://en.wikipedia.org/wiki/Adaptive_filter Accessed on 2008-11-22 [3] Rolf Limacher, Removal of power line interference from the ECG signal by an Adaptive digital filter, ETH Zurich, laboratory of Electrical Engineering Design Gloriast, Zurich [4] Applications of Adaptive Filtering to ECG Analysis, Noise Cancellation and Arrhythmia Detection Nitish V . Thakor, Seiiior Member, IEEE, and Yi-Sheng Zhu, Se~iior Momher, IEEE [5] http://www.eng.nus.edu.sg/EResnews/0410/sf/sf_7.html Accessed on 2008-11-23 [6] http://www2.netdoctor.co.uk/health_advice/examinations/ecg.htm Accessed on 2008-09-13

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noise analysis & qrs detection in ecg signals

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