Biosignal sampling & quantizaiton

Question 1

Bioelectrical singals

Answer 1

generated by nerves & muscles, elecrochemical changes within & between cells > generation of action potetnail = flow of ions across membrane
ECG, EGG, EEG, EMG

Question 2

Biomagnetic signals

Answer 2

• magnetic fields generated by brain/organs, typically accompanying electric field
• Biomagnatism: measurement of magnetic signals associated with specific physiological activity
• SQUID & MEG

Question 3

SQUID

Answer 3

superconduction quantum interface device

• very precise magnetic sensors or magnetometers
• monitoring of magentic activity

Question 4

MEG

Answer 4

Magnetoencepalography

• Principle: recording magnet fields in different positions produced by electrical currents occuring naturally in the brain
• technique for mapping brain activity
• allows to backcalculate intracellular current
• assessment of perceputal and cognitive brain processes

Question 5

Biochemical signals

Answer 5

• changes in concentration of various chemical agents in the body
• measure: changes in partial pressure of oxygen and carbon dioxide
• determine: normal levels

Question 6

Biomechanical signals

Answer 6

motion, displacement, force, pressure and flow

Question 7

Bioacoustic signals

Answer 7

special subset of biomechanical signals that involve vibrations

• bioogical events produce acoustic noise: flow of blood, respiratroy system, joints
• measured at the skin surface via microphones and accelerometers
• photoacoustic tomography of arthritic joints

Question 8

Biooptical signals

Answer 8

optical light ot induced attributes of biological systems

• fluorescnet characteristic of amniotic fluid
• dye dilution method (estimate cardiac output)
• red and infrared light (measurement of blood oxygen)

Question 9

characterisitcs of biosignals

Answer 9

• continuous
• discrete
• deterministic
• random /stochastic

Question 10

continuous biosignals

Answer 10

• almost all biosignals are continuous

- vary with time → converted into discrete signals → analyzed by computer

Question 11

discrete biosignals

Answer 11

• a series of specific signal values acquired at specific time points

Question 12

deterministic biosignals

Answer 12

described as periodic or transient mathematical funcitons

• periodic: usually composed of the sum of differnet sine waves ot sinusoid components
• transient: nonzero or vary over a finite time interval → decay to a constant value

Question 13

random / stochastic biosignals

Answer 13

• contain uncertainity in describing parameters
• mathematical funcitons cannot be used to precisely describe random signals
• are most often analysed using statistical techniques
• biosignals most often have some unpredictable noise or change in parameters

Question 14

components of signal acquisation

Answer 14

• A/D converters
• signal sampling
• quantization errors

Question 15

A/D converter

Answer 15

• transforms biological signals form continuous (analog) wavefrom to discrete (digital) sequences
• compunter controlled voltmeter: measures input signal and gives a numeric representation as output

Question 16

signal sampling

Answer 16

• Definition: process by whcih a continous singal is converted into a discrete sequence in time
• x(t) = analog singal → recording of the amplitude value of x(t) every T second

Question 17

sampling rate/ frequency fs

Answer 17

= equal to inverse of the sampling period → 1/T in Hz (s^-1)

• sampling rate used to dicretize a continous or analog singal → critical for generation of accurate approximation of waveform
• too low sampling rate leads to distortions

Question 18

Nyquist sampling theorem

Answer 18

f (nyquist) = 2 *f(max)

- the minimum sampling rate used should be at least twice the macimum frequency of the original signal

Question 19

quantization

Answer 19

definition: process of mapping a large set of input values to a smaller set by rounding values to some unit of precision → transformed into binary values

Question 20

Resolution of the A/D converter

Answer 20

• quantizer with N bits is capable of representing 2^N possible amplitude values
  input voltage range / 2^N = voltage resolution

Question 21

quantization error

Answer 21

• analog signal approximated by quantization function (digital) → set to best approx. value of the digital output line