1. “Victor Babes” UNIVERSITY OF MEDICINE AND PHARMACY TIMISOARA DEPARTMENT OF MEDICAL INFORMATICS AND BIOPHYSICS Medical Informatics Division www.medinfo.umft.ro/dim 2007 / 2008

2. BIOLOGICAL SIGNALS (I) AQUISITION. FILTERING PERIODICAL SIGNALS PROCESSING COURSE 7

3. 1. BIOLOGICAL SIGNALS AQUISITION

4. 1.1. DEFINITION1.1. DEFINITION TIME EVOLUTION OF A BIOLOGICAL VARIABLETIME EVOLUTION OF A BIOLOGICAL VARIABLE GENERAL SCHEME OF BIOSIGNAL ANALYSISGENERAL SCHEME OF BIOSIGNAL ANALYSIS

5. –1.2. CLASSIFICATION a) ON THEIR NATURE:a) ON THEIR NATURE: –ELECTRICAL (ECG, EEG, EMG etc) –NON-ELECTRICAL (pressure, concentration etc) b) ON EVOLUTIONb) ON EVOLUTION –PERIODICAL (ECG) –NON-PERIODICAL (EEG)

6. 1.3. AQUISITION SYSTEMS1.3. AQUISITION SYSTEMS ELECTRICAL SIGNALS : electrodesELECTRICAL SIGNALS : electrodes NON-ELECTRICAL: transducersNON-ELECTRICAL: transducers (pH, pressure etc) (pH, pressure etc)

7. 1.4. ANALOG - DIGITAL CONVERSION a) SAMPLINGa) SAMPLING DISCRETIZATION ON OX AXIS (time)DISCRETIZATION ON OX AXIS (time) SAMPLING PERIOD: T e (s)SAMPLING PERIOD: T e (s) –Time interval between two successive readings SAMPLING FREQUENCY: f e (Hz)SAMPLING FREQUENCY: f e (Hz) –Number of readings in time unit (nr./sec) f e = 1 / T e (1)

8. Example: recorded signal

9. SAMPLING

10. SAMPLING

11. SAMPLING

12. SAMPLING

14. a) SAMPLING THEOREM (Shannon) f e >= 2. F max (2) Sampling frequency should be at least twice the maximal frequency of the signalSampling frequency should be at least twice the maximal frequency of the signal NYQUIST FREQUENCY: 2.F max (Hz)NYQUIST FREQUENCY: 2.F max (Hz)

15. Good sampling

16. b) QUANTISING Discretization of OY axis (amplitude)Discretization of OY axis (amplitude) INTERVAL BETWEEN V MAX AND V MIN IS DIVIDED INTO “N” AMPLITUDE STEPSINTERVAL BETWEEN V MAX AND V MIN IS DIVIDED INTO “N” AMPLITUDE STEPS THE WIDTH OF A STEP (Quantum)THE WIDTH OF A STEP (Quantum)  V = (V Max - V min ) / N (3) Relation of N with n – number of bits used by ADC to express a readingRelation of N with n – number of bits used by ADC to express a reading N = 2 n (4)

17. Quantising

18. 1.5. A - D CONVERTERS MAXIMAL SAMPLING FREQUENCY (10 kHz - 1 MHz)MAXIMAL SAMPLING FREQUENCY (10 kHz - 1 MHz) NUMBER OF BITS (8 - 16)NUMBER OF BITS (8 - 16) INPUT RANGE (-10/+10 V, -0.1/+0.1 v)INPUT RANGE (-10/+10 V, -0.1/+0.1 v) NUMBER OF CHANNELS (MULTIPLEXING)NUMBER OF CHANNELS (MULTIPLEXING)

19. 1.4. FREQUENTIAL ANALYSIS SIGNAL REPRESENTATION:SIGNAL REPRESENTATION: –TEMPORAL Ampl = f (time) –FREQUENTIAL (spectrum) Ampl = f (freq)

20. b) FILTER ANALYSISb) FILTER ANALYSIS BAND - PASS FILTERS ( BAND - PASS FILTERS (  WAVES PROPORTIONS - mingographsWAVES PROPORTIONS - mingographs c) FOURIER ANALYSISc) FOURIER ANALYSIS Definition: SIGNAL DECOMPOSITION INTO FREQUENCIAL COMPONENTSDefinition: SIGNAL DECOMPOSITION INTO FREQUENCIAL COMPONENTS Domain: 0 - 30 HzDomain: 0 - 30 Hz Types of spectra:Types of spectra: –AMPLITUDE –POWER (proportional to A 2 )

21. Exemplu: semnal sinusoidal de 1 Hertz si spectrul sau

22. Semnal de 2 Hz

23. c) SPECTRAL RESOLUTIONc) SPECTRAL RESOLUTION –DEFINITION: distance between two neighbour points in the spectrum –RELATION WITH EPOCH LENGTH (recorded signal duration, in seconds)  f = 1 /  T (5) d) TIME CONSTANTd) TIME CONSTANT e) TESTS FOR SIGNALSe) TESTS FOR SIGNALS –STATIONARITY, NORMALITY AND TREND TESTS

24. Exemple - problem We record an EMG signal using a 10 bit ADC, with a sampling frequency of 500 Hz, recording epochs of 2 seconds. The input signal has values between 0 and 100  V. Calculate: A)Sampling period (in ms) B)Maximal frequency in the spectrum C)Spectral resolution D)Number of amplitude steps E)Reading precision (quantum value, how many  V correspond to 1 bit)

25. 2. FILTERING

26. 2.1. DEFINITION: removing or diminishing the perturbations 2.2. NOISE CLASSIFICATION (perturbations): a) PERIODICAL (pink noise = low frequencies) b) NON-PERIODICAL (white noise) 2.3. SIGNAL / NOISE RATIO (SNR, decibels dB) 2.4. FILTERING MODES ELECTRONIC FILTER (before ADC) NUMERIC FILTER (after ADC)

27. 2.5. TYPES OF FILTERS

28. 3. PROCESSING PERIODICAL SIGNALS ELECTROCARDIOGRAPHIC SIGNAL (ECG)

31. 3.2. ECG PROCESSING - PHASES

32. b) ARTIFACT ELIMINATIONb) ARTIFACT ELIMINATION ZERO LINEZERO LINE SMOOTHINGSMOOTHING c) QRS TYPIFICATIONc) QRS TYPIFICATION d) ST - T TYPIFICATIONd) ST - T TYPIFICATION ST SEGMENT AMPLITUDEST SEGMENT AMPLITUDE (in coronary diseases)(in coronary diseases) e) P - WAVE DETECTIONe) P - WAVE DETECTION VERY SMALL AMPLITUDEVERY SMALL AMPLITUDE

33. 3.3. ECG ANALYSIS:3.3. ECG ANALYSIS: RYTHMRYTHM INTERVALSINTERVALS AMPLITUDESAMPLITUDES SLOPESSLOPES 3.4. OTHER ANALYSES:3.4. OTHER ANALYSES: VECTOCARDIOGRAMSVECTOCARDIOGRAMS CARDIAC MAPPINGCARDIAC MAPPING LATE POTENTIALS, ARRHYTMIASLATE POTENTIALS, ARRHYTMIAS

34. - e n d -