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Subtraction Method for Removing Powerline Interference from ECG

The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004. 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

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Subtraction Method for Removing Powerline Interference from ECG

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  1. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Subtraction Method for Removing Powerline Interference from ECG Chavdar Levkov1, Georgy Mihov2, Ratcho Ivanov2, Ivan K. Daskalov 3 Ivaylo Christov3, Ivan Dotsinsky3 1SIGNACOR laboratory, Lyubliana str. No 46, office 706, 1618 Sofia, Bulgaria, info@signacor.com 2Faculty of Electronic Engineering and Technologies (FETT), Technical University – Sofia, Kl. Ohridsky str. No 8, block 1, 1797 Sofia, Bulgaria, gsm@tu-sofia.bg 3Centre of Biomedical Engineering, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bl. 105, 1113 Sofia, Bulgaria, iadoc@bas.bg Bulgaria, Sozopol, September 22 - 24, 2004 1

  2. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 In Memoriam of Professor Ivan Konstantinov Daskalov Bulgaria, Sozopol, September 22 - 24, 2004 2

  3. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 1. Introduction The background - beginning in 1979 • - Contract No 1238-23/79 named “Microprocessor based ECG selector for Screening Analysis” • - 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; • - 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. Bulgaria, Sozopol, September 22 - 24, 2004 3

  4. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 The problem Removing the Powerline interference from ECG. Analysis 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. Bulgaria, Sozopol, September 22 - 24, 2004 4

  5. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’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). The solution Bulgaria, Sozopol, September 22 - 24, 2004 5

  6. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Bulgarian Patent - 1980 [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 30792 30.06.1980, (in Bulgarian). Bulgaria, Sozopol, September 22 - 24, 2004 6

  7. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 First Publication - 1981 [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, 97-100 (in Bulgarian). Bulgaria, Sozopol, September 22 - 24, 2004 7

  8. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 First Device - ECG Selector - 1981 [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, 93-96 (in Bulgarian). Bulgaria, Sozopol, September 22 - 24, 2004 8

  9. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 First Ph.D Thesis - 1983 [4] Mihov G. Software automated electronic devi-ces for processing and visualization of electrocar-diosignals. Ph.D. thesis, TU-Sofia, 1983 (in Bulgarian). Bulgaria, Sozopol, September 22 - 24, 2004 9

  10. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 First Publication Abroad - 1984 [5] Levkov, C., Mihov, G., Ivanov, R., and Daskalov. I., 1984, Subtraction of 50 Hz interference from the electrocardiogram. Medical & Biological Engineering & Computing, 22, 371-373. Bulgaria, Sozopol, September 22 - 24, 2004 10

  11. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 New Investigations - 1988 [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, 431-434. Bulgaria, Sozopol, September 22 - 24, 2004 11

  12. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 2. The Subtraction Method Basal Structure of the Subtraction Method Bulgaria, Sozopol, September 22 - 24, 2004 12

  13. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Main Stages • – 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 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. Bulgaria, Sozopol, September 22 - 24, 2004 13

  14. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 2.1. Linear segment detection b: Aproximate frequency spectrum of a linear segment a: Typical linear and non-linear segments of a real ECG signal Criteria for linearity is based on the second difference (signed Di) of the ECG. Di is compared with a threshold M which is obtained experimentally: Bulgaria, Sozopol, September 22 - 24, 2004 14

  15. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Getting the second difference from linear segments of the ECG. Maximal and minimal length for analysing a: for odd multiplicity; b: for even multiplicity Sampling rate ФPowerline frequency FSampling period N = Φ/F In even multiple sampling N is integer and = 2nIn odd multiple sampling N is integer and = 2n+1In non-multiple sampling N is rationale. Bulgaria, Sozopol, September 22 - 24, 2004 15

  16. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’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. Bulgaria, Sozopol, September 22 - 24, 2004 16

  17. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 2.2. Interference extracting Different filters for interference removing (K-filter) are used: - filter for odd multiplicity [8, 9] - - filter for even multiplicity with a linear phase response [7, 8] - - ‘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. The interference samples Bi are calculated (extracted) by: Bulgaria, Sozopol, September 22 - 24, 2004 17

  18. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 2.3. Interference restoring Case of multiple sampling 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) : Content of the temporary buffer (N* is the rounded value of N) The restored value of the interference is calculated by: Requirements to the B-filter:- Unity gain for f = F;- Linear phase response. Bulgaria, Sozopol, September 22 - 24, 2004 18

  19. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 3. Experiments and Results 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] Bulgaria, Sozopol, September 22 - 24, 2004 19

  20. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Experimental data, presented at the Academic Lecture of Prof. Ivan K. Daskalov, February, 27, 2003 Bulgaria, Sozopol, September 22 - 24, 2004 20

  21. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 How to test the method objectively? Test for odd multiple sampling, F=50 Hz and Ф=250 Hz. 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. Bulgaria, Sozopol, September 22 - 24, 2004 21

  22. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Test for non-multiple sampling, F=60 Hz and Ф=250 Hz. Bulgaria, Sozopol, September 22 - 24, 2004 22

  23. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 4. Acknowledgements 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. Bulgaria, Sozopol, September 22 - 24, 2004 23

  24. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 5. Discussion and Conclusions Contribution of the PaperTheoretical generalization of the Subtraction Method for Removing Powerline Interference from ECG and its Application. 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). Bulgaria, Sozopol, September 22 - 24, 2004 24

  25. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’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, 635-638.[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, 147-150.[17] Monaco, A. Sviluppo di un modulo software per la gestione di unsistema per il controllo remoto dei portatori di pacemaker. Tesi di laureain tecnologie biomediche, Universitа degli studi di Napoli 'Federico II',Facoltа di ingegneria, Dipartimento di Ingegneria Elettronica e delleTelecomunicazioni. 2000 (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. Bulgaria, Sozopol, September 22 - 24, 2004 25

  26. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’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). Bulgaria, Sozopol, September 22 - 24, 2004 26

  27. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 6.References [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 30792 30.06.1980, (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, 97-100 (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, 93-96 (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, 371-373.[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, 431-434.[7] Dotsinsky, I. A., I. K. Daskalov, Comments on ‘Dynamic Levkov-Christov subtraction of mains interference’. Med. & Biol. Eng. & Comput., 33, 1995, 360. Bulgaria, Sozopol, September 22 - 24, 2004 27

  28. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’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, 197-202 (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. 87-93.[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. 189-191.[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. 183-185.[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, 147-150. Bulgaria, Sozopol, September 22 - 24, 2004 28

  29. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 [17] Monaco, A. Sviluppo di un modulo software per la gestione di unsistema per il controllo remoto dei portatori di pacemaker. Tesi di laureain tecnologie biomediche, Universitа degli studi di Napoli 'Federico II',Facoltа di ingegneria, Dipartimento di Ingegneria Elettronica e delleTelecomunicazioni. 2000 (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, 169-172.[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, 357-358.[22] Bazhyna A., I. Christov, A. Gotchev, I. Daskalov, K. Egiazarian. Powerline Interference Suppression in High-Resolution ECG. Computers in Cardiology, 2003, 30, pp. 561-564. The paper has been reviewed by Professor Ph.D. Stefan Tabakovfrom Technical University – Sofia Bulgaria, Sozopol, September 22 - 24, 2004 29

  30. The Thirteen International Scientific and Applied Science Conference ELECTRONICS - ET’2004 Assoc. Prof. D.Sc. Chavdar Levkov Assoc. Prof. Ph.D. Georgy Mihov Prof. Ph.D. Ratcho Ivanov Prof. D.Sc. Ivan K. Daskalov Assoc. Prof. Ph.D. Ivaylo Christov Prof. D.Sc Ivan Dotsinsky Bulgaria, Sozopol, September 22 - 24, 2004 30

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