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Subtraction Method for Removing Powerline Interference from ECG Chavdar Levkov 1, Georgy Mihov 2, Ratcho Ivanov 2, Ivan K. Daskalov 3 Ivaylo Christov 3,

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Presentation on theme: "Subtraction Method for Removing Powerline Interference from ECG Chavdar Levkov 1, Georgy Mihov 2, Ratcho Ivanov 2, Ivan K. Daskalov 3 Ivaylo Christov 3,"— Presentation transcript:

1 Subtraction Method for Removing Powerline Interference from ECG Chavdar Levkov 1, Georgy Mihov 2, Ratcho Ivanov 2, Ivan K. Daskalov 3 Ivaylo Christov 3, Ivan Dotsinsky 3 1 SIGNACOR laboratory, Lyubliana str. No 46, office 706, 1618 Sofia, Bulgaria, 2 Faculty of Electronic Engineering and Technologies (FETT), Technical University – Sofia, Kl. Ohridsky str. No 8, block 1, 1797 Sofia, Bulgaria, 3 Centre of Biomedical Engineering, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bl. 105, 1113 Sofia, Bulgaria, The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September ,

2 In Memoriam of Professor Ivan Konstantinov Daskalov The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September ,

3 1. Introduction - Contract No /79 named “Microprocessor based ECG selector for Screening Analysis” - Contract No /79 named “Microprocessor based ECG selector for Screening Analysis” - Contractor - Institute for Medical Equipment, Sofia; - Contractor - Institute for Medical Equipment, Sofia; - Developer - Research Sector of Higher Mechanical and Electrotechnical Institute - now Technical University – Sofia with director of the project Prof. V. Zlatarov, technical research manager R. Ivanov and technical assistant G. Mihov; - Developer - Research Sector of Higher Mechanical and Electrotechnical Institute - now Technical University – Sofia with director of the project Prof. V. Zlatarov, technical research manager R. Ivanov and technical assistant G. Mihov; - Collaborator - Central Laboratory for Electromedical Instrumentation (CLEMA) at the Medical Academy Sofia with director Prof. I. K. Daskalov and research assistants Ch. Levkov and M. Matveev. - Collaborator - Central Laboratory for Electromedical Instrumentation (CLEMA) at the Medical Academy Sofia with director Prof. I. K. Daskalov and research assistants Ch. Levkov and M. Matveev. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 The background - beginning in

4 The problem Removing the Powerline interference from ECG. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 Powerline interference can be removed with classical linear filters. However, important spectral components of the ECG are affected. After the filtration the low frequency components are preserved. P, T waves and S-T segments are undistorted. But important frequency components in ECG are affected which leads to unacceptable distortions of the shape of the QRS complex. Analysis 4

5 The solution The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 Linear digital filtration is applied only in these segments where the ECG frequency components are not affected (in so called linear segments). At the same time the powerline interference signal is extracted and saved. Later on this interference signal is subtracted from the other non-linear segments of the ECG (e.g in the QRS complex). 5

6 Bulgarian Patent The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 [1] Levkov C., Mihov G., Ivanov R., and Daskalov. I. Method and device for elimination of power- line frequency disturbance during analysis of biological signals. Bulgarian Patent No , (in Bulgarian). [1] Levkov C., Mihov G., Ivanov R., and Daskalov. I. Method and device for elimination of power- line frequency disturbance during analysis of biological signals. Bulgarian Patent No , (in Bulgarian). 6

7 First Publication The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 [2] Daskalov I., Ivanov R., Levkov C. and Mihov G. Elimination of power-line frequency disturbance by microprocessor. Proceedings of the XVI Scientific Session “Radio day ‘81”, May 1981, Sofia, (in Bulgarian). [2] Daskalov I., Ivanov R., Levkov C. and Mihov G. Elimination of power-line frequency disturbance by microprocessor. Proceedings of the XVI Scientific Session “Radio day ‘81”, May 1981, Sofia, (in Bulgarian). 7

8 First Device - ECG Selector The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 [3] Daskalov I., Ivanov R. and Mihov G. Microprocessor controlled ECG slector for screening analysis. Proceedings of the XVI Scientific Session “Radio day ‘81”, May 1981, Sofia, (in Bulgarian). [3] Daskalov I., Ivanov R. and Mihov G. Microprocessor controlled ECG slector for screening analysis. Proceedings of the XVI Scientific Session “Radio day ‘81”, May 1981, Sofia, (in Bulgarian). 8

9 First Ph.D Thesis The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 [4] Mihov G. Software automated electronic devi-ces for processing and visualization of electrocar- diosignals. Ph.D. thesis, TU-Sofia, 1983 (in Bulgarian). [4] Mihov G. Software automated electronic devi-ces for processing and visualization of electrocar- diosignals. Ph.D. thesis, TU-Sofia, 1983 (in Bulgarian). 9

10 First Publication Abroad The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 [5] Levkov, C., Mihov, G., Ivanov, R., and Daskalov. I., 1984, Subtraction of 50 Hz interference from the electrocardiogram. Medical & Biological Engineering & Computing, 22, [5] Levkov, C., Mihov, G., Ivanov, R., and Daskalov. I., 1984, Subtraction of 50 Hz interference from the electrocardiogram. Medical & Biological Engineering & Computing, 22,

11 New Investigations The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 [6] Christov, I. and Dotsinsky, I., 1988, New approach to the digital elimination of 50 Hz interference from the electrocardiogram. Medical & Biological Engineering & Computing, 26, [6] Christov, I. and Dotsinsky, I., 1988, New approach to the digital elimination of 50 Hz interference from the electrocardiogram. Medical & Biological Engineering & Computing, 26,

12 2. The Subtraction Method The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 Basal Structure of the Subtraction Method 12

13 Main Stages The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 – Linear segment detection. Every ECG sample is tested whether it belongs to a linear segment. A special criteria for linearity is used for this purpose; – Linear segment detection. Every ECG sample is tested whether it belongs to a linear segment. A special criteria for linearity is used for this purpose; – Interference extracting. If the criteria for linearity is fulfilled the powerline interference is extracted with appropriate digital filter. At the same time the interference is removed from these linear ECG segments; – Interference extracting. If the criteria for linearity is fulfilled the powerline interference is extracted with appropriate digital filter. At the same time the interference is removed from these linear ECG segments; – Interference restoring. The extracted values of the interference are saved in FIFO buffer. After appropriate amplitude and phase processing they are used for restoring the interference; – Interference restoring. The extracted values of the interference are saved in FIFO buffer. After appropriate amplitude and phase processing they are used for restoring the interference; – Interference subtracting. The restored values of the interference are subtracted from the original signal in non-linear segments. – Interference subtracting. The restored values of the interference are subtracted from the original signal in non-linear segments. 13

14 2.1. Linear segment detection The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 a: Typical linear and non-linear segments of a real ECG signal Criteria for linearity is based on the second difference (signed D i ) of the ECG. D i is compared with a threshold M which is obtained experimentally: b: Aproximate frequency spectrum of a linear segment 14

15 The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 Getting the second difference from linear segments of the ECG. Maximal and minimal length for analysing Sampling rate Ф Powerline frequency F Sampling period  N = Φ/F In even multiple sampling N is integer and = 2n In odd multiple sampling N is integer and = 2n+1 In non-multiple sampling N is rationale. a: for odd multiplicity; b: for even multiplicity 15

16 The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 Different Criteria for linearity (D-filter) are used: - Longest interval; - Shortest interval for odd multiplicity; - Shortest interval for even multiplicity; - Complex criteria [4, 5]; - Criteria for even multiplicity [6]; - Criteria for even multiplicity [7]; Transfer function of D-filter - longest interval Requirements to the D-filter: - Gain zero for f = 0 Hz; - Gain zero for f = F. 16

17 The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 Different filters for interference removing (K-filter) are used: - ‘three-point’ filter [11] - Transfer function of K-filter Requirements to the K-filter: - Unity gain for f = 0 Hz; - Gain zero for f = F; - Linear phase response Interference extracting - filter for odd multiplicity [8, 9] - - filter for even multiplicity with a linear phase response [7, 8] - The interference samples B i are calculated (extracted) by: 17

18 The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 Case of multiple sampling Requirements to the B-filter: - Unity gain for f = F; - Linear phase response Interference restoring The interference is cancelled by subtracting the corresponding interference value with appropriate phase taken from the FIFO buffer: Case of non-multiple sampling A digital filter is applied for the values in the buffer (B-filter) : The restored value of the interference is calculated by: (N * is the rounded value of N) Content of the temporary buffer 18

19 3. Experiments and Results The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 The experimental verification is carried out on large real ECG databases. American Heart Association Holter and 8-standard leads data bases are used. Experiment with non-stationary interference. M=160 μV, F=50 Hz and Ф=400 Hz [6] 19

20 The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 Experimental data, presented at the Academic Lecture of Prof. Ivan K. Daskalov, February, 27,

21 The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 How to test the method objectively? A Take a “clean” ECG record without interference. B Add to the record an interference signal. C Perform the filtration. D Subtract the corresponding samples of the clean and filtered record to obtain the error signal. E Visually and statistically evaluate the error signal. Test for odd multiple sampling, F=50 Hz and Ф=250 Hz. 21

22 The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 Test for non-multiple sampling, F=60 Hz and Ф=250 Hz. 22

23 4. Acknowledgements The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 We would like to acknowledge the contributions of: Cveta Georgieva Ph.D. student for her theoretical research of the total transfer function of the subtraction method and Todor Stoyanov Ph.D student for research in software synchronisation of the sampling rate to the powerline frequency. 23

24 5. Discussion and Conclusions The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 Ph.D and Dr.Sc thesises in Bulgaria [4] Mihov G. Software automated electronic devices for processing and visualization of electrocardiosignals. Ph.D. thesis, TU-Sofia, 1983 (in Bulgarian). [12] Levkov Ch. Engineering support of automated electrocardiography. D. Sc. thesis, Sofia, 1987 (in Bulgarian). [13] Dotsinsky I. Methods and Devices for ECG Signal Analysis. D.Sc. thesis, Sofia, 1986 (in Bulgarian). [14] Christov, I. ECG Signals Pick-up, Processing and Display. Ph.D. thesis, Sofia, 1988 (in Bulgarian). Contribution of the Paper Theoretical generalization of the Subtraction Method for Removing Powerline Interference from ECG and its Application. 24

25 The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 Papers and Publications - Citations in 46 papers from Bulgaria, Germany, France, China, USA, Canada etc. - The method has been applied from other scientists: [15] Yan, X. G. Dynamic Levkov – Christov subtraction of mains interference. Medical & Biological Engineering & Computing, 1993, 31, [16] Gang Li, Lin Ling, Yu Qilian, Yu Xuemin. A new adaptive coherent model algorithm for removal of power-line interference. J. of Clinical. Engng, 1995, 20, No 2, [17] Monaco, A. Sviluppo di un modulo software per la gestione di un sistema per il controllo remoto dei portatori di pacemaker. Tesi di laurea in tecnologie biomediche, Universitа degli studi di Napoli 'Federico II', Facoltа di ingegneria, Dipartimento di Ingegneria Elettronica e delle Telecomunicazioni (in Italian). - The method has been applied for different type of signals: [18] K. E. Butler, R. D. Russell “Cancellation on Multiple Harmonic Noise Series in Geophysical Records”, Geophysics, Jan. 8, 2003, Canada. 25

26 The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 Future research and improvements - Improvement of criteria for linearity in order to avoid false recognition of linear segments; - Theoretical evaluation of the total transfer function of the subtraction method including non-linear segments; - Real time processing for the case where the interference is non- stationary. - Real-time processing when ECG signal is sampled in very high rate (oversampling). 26

27 6. References The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 [1] Levkov C., Mihov G., Ivanov R., and Daskalov. I. Method and device for elimination of power-line frequency disturbance during analysis of biological signals. Bulgarian Patent No , (in Bulgarian). [2] Daskalov I., Ivanov R., Levkov C. and Mihov G. Elimination of power-line frequency disturbance by microprocessor. Proceedings of the XVI Scientific Session “Radio day ‘81”, May 1981, Sofia, (in Bulgarian). [3] Daskalov I., Ivanov R. and Mihov G. Microprocessor controlled ECG slector for screening analysis. Proceedings of the XVI Scientific Session “Radio day ‘81”, May 1981, Sofia, (in Bulgarian). [4] Mihov G. Software automated electronic devices for processing and visualization of electrocardiosignals. Ph.D. thesis, TU-Sofia, 1983 (in Bulgarian). [5] Levkov, C., Mihov, G., Ivanov, R., and Daskalov. I., 1984, Subtraction of 50 Hz interference from the electrocardiogram. Medical & Biological Engineering & Computing, 22, [6] Christov, I. and Dotsinsky, I., 1988, New approach to the digital elimination of 50 Hz interference from the electrocardiogram. Medical & Biological Engineering & Computing, 26, [7] Dotsinsky, I. A., I. K. Daskalov, Comments on ‘Dynamic Levkov-Christov subtraction of mains interference’. Med. & Biol. Eng. & Comput., 33, 1995,

28 The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 [8] Mihov G. Elimination of non-synchronized power-line frequency disturbance from ECG signal. Proceedings of the Anniversary “50 years TU-Sofia” National Scientific Conference “Electronics ’95, Sozopol, book 3, (in Bulgarian). [9] Georgieva, T. and Mihov. G., 2002, On-line subtraction method for mains interference removing from ECG signals with signal processor. Proceedings of the 6th International Symposium ‘Microelectronics Technologies and Microsystems’, November 20-22, Lviv, Ukraine, pp [10] Mihov, G., 1996, Elimination of Mains Interference from the ECG in Non-Syncronized Sampling: A Theoretical Approach. Proceedings of the 13-th biennial international conference BIOSIGNAL’96, Brno, Czechoslovakia. pp [11] Levkov, C. and Mihov, G., 1996, Rejection – subtraction filter of mains interference from the ECG. Proceedings of the 13-th biennial international conference BIOSIGNAL’96, Brno, Czechoslovakia. pp [12] Levkov Ch. Engineering support of automated electrocardiography. D. Sc. thesis, Sofia, 1987 (in Bulgarian). [13] Dotsinsky I. Methods and Devices for ECG Signal Analysis. D.Sc. thesis, Sofia, 1986 (in Bulgarian). [14] Christov, I. ECG Signals Pick-up, Processing and Display. Ph.D. thesis, Sofia, 1988 (in Bulgarian). [16] Gang Li, Lin Ling, Yu Qilian, Yu Xuemin. A new adaptive coherent model algorithm for removal of power-line interference. J. of Clinical. Engng, 1995, 20, No 2,

29 The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 [19] Dotsinsky I., I. Daskalov. Suppressing of Poverline Interference in Electrocardiogram. "Е+Е", 5-6/1996, 32 –38 (in Bulgarian). [17] Monaco, A. Sviluppo di un modulo software per la gestione di un sistema per il controllo remoto dei portatori di pacemaker. Tesi di laurea in tecnologie biomediche, Universitа degli studi di Napoli 'Federico II', Facoltа di ingegneria, Dipartimento di Ingegneria Elettronica e delle Telecomunicazioni (in Italian). [18] K. E. Butler, R. D. Russell (2003) “Cancellation on Multiple Harmonic Noise Series in Geophysical Records”, Geophysics, Jan. 8, Canada. [19] Dotsinsky I., I. Daskalov. Suppressing of Poverline Interference in Electrocardiogram. "Е+Е", 5-6/1996, 32 –38 (in Bulgarian). [20] Christov, I., 2000, Dynamic powerline interference subtraction from biosignals. Medical Engineering & Technology, 24, [21] Daskalov, I., Dotsinsky I. Reader respond to “A new adaptive coherent model algorithm for removal of power-line interference”. J. of Clinical Engng., September/October, 1995, [22] Bazhyna A., I. Christov, A. Gotchev, I. Daskalov, K. Egiazarian. Powerline Interference Suppression in High-Resolution ECG. Computers in Cardiology, 2003, 30, pp The paper has been reviewed by Professor Ph.D. Stefan Tabakov from Technical University – Sofia 29

30 The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgaria, Sozopol, September , 2004 Assoc. Prof. D.Sc. Chavdar Levkov Assoc. Prof. Ph.D. Georgy Mihov Prof. Ph.D. Ratcho Ivanov Prof. D.Sc. Ivan K. Daskalov Prof. D.Sc Ivan Dotsinsky Ivan Dotsinsky Assoc. Prof. Ph.D. Ivaylo Christov 30


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