“ “ Victor Babes” Victor Babes” UNIVERSITY OF MEDICINE UNIVERSITY OF MEDICINE AND PHARMACY AND PHARMACY TIMISOARA TIMISOARA DEPARTMENT OF DEPARTMENT OF MEDICAL INFORMATICS AND BIOPHYSICS MEDICAL INFORMATICS AND BIOPHYSICS Medical Informatics Division Medical Informatics Division www.medinfo.umft.ro/dim www.medinfo.umft.ro/dim 2007 / 2008 2007 / 2008
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“Victor Babes” UNIVERSITY OF MEDICINE AND PHARMACY TIMISOARA
“Victor Babes” UNIVERSITY OF MEDICINE AND PHARMACY TIMISOARA. DEPARTMENT OF MEDICAL INFORMATICS AND BIOPHYSICS Medical Informatics Division www.medinfo.umft.ro/dim 2007 / 2008. BIOLOGICAL SIGNALS (I) AQUISITION. FILTERING PERIODICAL SIGNALS PROCESSING. COURSE 7. - PowerPoint PPT Presentation
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““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
• 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)
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)
• 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