““Victor Babes” Victor Babes” UNIVERSITY OF MEDICINE UNIVERSITY OF MEDICINE

AND PHARMACY AND PHARMACY TIMISOARATIMISOARA

““Victor Babes” Victor Babes” UNIVERSITY OF MEDICINE UNIVERSITY OF MEDICINE

AND PHARMACY AND PHARMACY TIMISOARATIMISOARA

DEPARTMENT OFDEPARTMENT OF

MEDICAL INFORMATICS AND BIOPHYSICSMEDICAL INFORMATICS AND BIOPHYSICS

Medical Informatics DivisionMedical Informatics Divisionwww.medinfo.umft.ro/dimwww.medinfo.umft.ro/dim

2007 / 20082007 / 2008

BIOLOGICAL SIGNALS (I)BIOLOGICAL SIGNALS (I)

AQUISITION. FILTERINGAQUISITION. FILTERING

PERIODICAL SIGNALS PERIODICAL SIGNALS PROCESSINGPROCESSING

COURSE 7COURSE 7

1. BIOLOGICAL 1. BIOLOGICAL SIGNALS SIGNALS

AQUISITIONAQUISITION

• 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

–1.2. CLASSIFICATION1.2. CLASSIFICATION

• a) ON THEIR NATURE:a) ON THEIR NATURE:– ELECTRICAL (ECG, EEG, EMG etc)ELECTRICAL (ECG, EEG, EMG etc)– NON-ELECTRICAL (pressure, concentration etc)NON-ELECTRICAL (pressure, concentration etc)

• b) ON EVOLUTIONb) ON EVOLUTION– PERIODICAL (ECG)PERIODICAL (ECG)– NON-PERIODICAL (EEG)NON-PERIODICAL (EEG)

• 1.3. AQUISITION SYSTEMS1.3. AQUISITION SYSTEMS• ELECTRICAL SIGNALS : electrodesELECTRICAL SIGNALS : electrodes

• NON-ELECTRICAL: transducersNON-ELECTRICAL: transducers

• (pH, pressure etc) (pH, pressure etc)

1.4. ANALOG - DIGITAL 1.4. ANALOG - DIGITAL CONVERSIONCONVERSION

• a) SAMPLINGa) SAMPLING• DISCRETIZATION ON OX AXIS (time)DISCRETIZATION ON OX AXIS (time)

• SAMPLING PERIOD: TSAMPLING PERIOD: Tee (s) (s)

– Time interval between two successive readingsTime interval between two successive readings

• SAMPLING FREQUENCY: fSAMPLING FREQUENCY: fee (Hz) (Hz)

– Number of readings in time unit (nr./sec)Number of readings in time unit (nr./sec)

ffee = 1 / T = 1 / Tee (1) (1)

Example: recorded signal

SAMPLINGSAMPLING

SAMPLINGSAMPLING

SAMPLINGSAMPLING

SAMPLINGSAMPLING

a) SAMPLING THEOREM a) SAMPLING THEOREM

(Shannon)(Shannon)

ffee >= 2 . F >= 2 . Fmax max (2)(2)• Sampling frequency should be at least Sampling frequency should be at least

twice the maximal frequency of the signaltwice the maximal frequency of the signal

• NYQUIST FREQUENCY: 2.FNYQUIST FREQUENCY: 2.Fmaxmax (Hz) (Hz)

Good samplingGood sampling

Shortcut to St.exe.pif

b) QUANTISINGb) QUANTISING• Discretization of OY axis (amplitude)Discretization of OY axis (amplitude)

• INTERVAL BETWEEN VINTERVAL BETWEEN VMAXMAX AND V AND VMINMIN IS DIVIDED INTO “N” IS DIVIDED INTO “N”

AMPLITUDE STEPSAMPLITUDE STEPS

• THE WIDTH OF A STEP (Quantum)THE WIDTH OF A STEP (Quantum)

V = (V V = (V MaxMax - V - V minmin ) / N ) / N (3)(3)• Relation of N with n – number of bits used by ADC to express a Relation of N with n – number of bits used by ADC to express a

readingreading

N = 2N = 2 n n (4) (4)

QuantisingQuantising

1.5. A - D CONVERTERS1.5. A - D CONVERTERS

• MAXIMAL SAMPLING FREQUENCY MAXIMAL SAMPLING FREQUENCY (10 kHz - 1 MHz)(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 NUMBER OF CHANNELS (MULTIPLEXING)(MULTIPLEXING)

1.4. FREQUENTIAL ANALYSIS1.4. FREQUENTIAL ANALYSIS

• SIGNAL REPRESENTATION:SIGNAL REPRESENTATION:– TEMPORAL TEMPORAL

Ampl = f (time)Ampl = f (time)

– FREQUENTIAL (spectrum) FREQUENTIAL (spectrum) Ampl = f (freq)Ampl = f (freq)

• b) FILTER ANALYSISb) FILTER ANALYSIS• BAND - PASS FILTERS (BAND - PASS FILTERS (• WAVES PROPORTIONS - mingographsWAVES PROPORTIONS - mingographs

• c) FOURIER ANALYSISc) FOURIER ANALYSIS• Definition: SIGNAL DECOMPOSITION Definition: SIGNAL DECOMPOSITION

INTO FREQUENCIAL COMPONENTSINTO FREQUENCIAL COMPONENTS• Domain: 0 - 30 HzDomain: 0 - 30 Hz• Types of spectra: Types of spectra:

– AMPLITUDEAMPLITUDE– POWER (proportional to APOWER (proportional to A22))

Exemplu: semnal sinusoidal de 1 Hertz si spectrul sau

Semnal de 2 HzSemnal de 2 Hz

• c) SPECTRAL RESOLUTIONc) SPECTRAL RESOLUTION– DEFINITION: DEFINITION: distance between two neighbour distance between two neighbour

points in the spectrumpoints in the spectrum– RELATION WITH EPOCH LENGTH RELATION WITH EPOCH LENGTH (recorded (recorded

signal duration, in seconds)signal duration, in seconds)

f = 1 / f = 1 / T (5)T (5)• d) TIME CONSTANT d) TIME CONSTANT • e) TESTS FOR SIGNALSe) TESTS FOR SIGNALS

– STATIONARITY, NORMALITY AND TREND STATIONARITY, NORMALITY AND TREND TESTSTESTS

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)

2. FILTERING2. FILTERING

2.1. DEFINITION: removing or diminishing the 2.1. DEFINITION: removing or diminishing the perturbationsperturbations

2.2. NOISE CLASSIFICATION (perturbations):2.2. NOISE CLASSIFICATION (perturbations):

a) PERIODICAL (pink noise = low a) PERIODICAL (pink noise = low frequencies)frequencies)

b) NON-PERIODICAL (white noise)b) NON-PERIODICAL (white noise)

2.3. SIGNAL / NOISE RATIO 2.3. SIGNAL / NOISE RATIO (SNR, decibels dB)(SNR, decibels dB)

2.4. FILTERING MODES2.4. FILTERING MODESELECTRONIC FILTER (before ADC)ELECTRONIC FILTER (before ADC)

NUMERIC FILTER (after ADC)NUMERIC FILTER (after ADC)

2.5. TYPES OF FILTERS

3. PROCESSING 3. PROCESSING PERIODICAL SIGNALSPERIODICAL SIGNALS

ELECTROCARDIOGRAPHIC ELECTROCARDIOGRAPHIC

SIGNAL (ECG)SIGNAL (ECG)

3.2. ECG PROCESSING - 3.2. ECG PROCESSING - PHASESPHASES

• b) ARTIFACT ELIMINATIONb) ARTIFACT ELIMINATION• ZERO LINEZERO LINE• SMOOTHINGSMOOTHING

• c) QRS TYPIFICATIONc) QRS TYPIFICATION

• d) ST - T TYPIFICATIONd) ST - T TYPIFICATION• ST SEGMENT AMPLITUDE ST SEGMENT AMPLITUDE • (in coronary diseases)(in coronary diseases)

• e) P - WAVE DETECTIONe) P - WAVE DETECTION• VERY SMALL AMPLITUDEVERY SMALL AMPLITUDE

• 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

- e n d -- e n d -