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Medical Physics > Biosignals > Flashcards

Biosignals Flashcards

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1
Q

What are biosignals?

A

A biosignal is any signal in living beings that can be continually measured and monitored.
They are descriptions of physiological phenomena.

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2
Q

How can biosignals be characterised?

A

1) according to their ORIGIN,
2) DISCRETE or CONTINUOUS
3) DETERMINISTIC or RANDOM

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3
Q

What is meant by “origin” (when characterising signals)?

A

the source that generates the signal.

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4
Q

What are the different origins of biosignals?

A

1) ELECTRIC: eg. the depolarization of a nerve cell
2) MECHANICAL: eg. the sound generated by heart valves
3) CHEMICAL: eg. the concentration of CO2 in the blood.

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5
Q

What are “continuous” signals?

A

signals that are defined at any moment in time.

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6
Q

What are “discrete” signals?

A

signals only defined at discrete points in time.

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7
Q

What is sampling?

A

sampling is the deduction of a continuous signal to a discrete signal.

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8
Q

What are “deterministic” signals?

A

signals which can be described by explicit mathematical relationships.

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9
Q

What are “random” signals?

A

signals which cannot be exactly expressed.

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10
Q

What do “deterministic” signals further speciate into?

A

1) periodic signals
2) almost periodic signals
3) transient signals

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11
Q

What do “random” signals further speciate into?

A

1) stationary signals
2) non-stationary signals

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12
Q

Why do determnistic signals further speciate?

A

depending on their reoccurrence.

PERIODIC: reoccur often.
eg. sine wave.

ALMOST PERIODIC: reoccur, yet less often and less precisely.
eg. ECG

TRANSCIENT: do not have a pattern.
eg, cell response.

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13
Q

When do random signals develop?

A

During random processes, e.g.: a group of muscle cells that depolarize in a more or less random fashion.

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14
Q

What are stationary random biosignals?

A

signal properties that are random, yet do not change over time.
eg. patient is in a stable condition.
eg. alpha waves

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15
Q

What are nonstationary random biosignals?

A

if signal properties are random and changing.
eg. EEG

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16
Q

What are biosignals usually a function of?

A

time

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17
Q

When can the signal waveshape be fully determined?

A

Once all parameters are known.
eg. sin wave requires: amplitude, frequency, and phase.

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18
Q

What characteristics of biosignals are important?

A
  • amplitude
  • frequency
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19
Q

What is a frequency spectrum?

A

a collection of frequencies and corresponding amplitudes and magnitudes

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20
Q

What is an electroencephalogram (EEG) used for?

A

biosignalling reflecting the electrical activity of neurons.

amplitude < 0.1mv
frequency spectrum: 3-200Hz

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21
Q

What is an electrocardiogram (ECG) used for?

A

reflects the electric activity of the heart.

amplitude < 5 mv
frequency spectrum: 0.3-200Hz

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22
Q

What is a phonocardiogram (PCG) used for?

A

represents the sounds of a heart.

frequency spectrum: 30-2000Hz

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23
Q

What type of biosignals are blood pressure curves?

A

low-frequency biosignals of MECHANICAL origin.

24
Q

What detects a biosignal?

A

A sensor

25
Q

What do sensors do to non-electric signals? Why is this completed?

A

convert non-electric signals to electric signals so that they can be amplified, filtered and recognised by electronic interferance.

26
Q

Where are biosignals stored and processed?

A

In the system for signal processing.

27
Q

What are sensors?

A

special devices used to provide an interference between signals from the biological systems and the instrument recording them.

28
Q

What are different names for sensors?

A
  • transducers
  • converters
  • detectors
    etc.
29
Q

What can sensors be? How do they classify?

A

1) Active
2) Passive

30
Q

What is an active sensor used for?

A

used to convert other types of energy to electric power (thermocouple, piezoelectric sensor, etc.)

31
Q

What is a passive sensor used for?

A

used for the detection of biosignals directly or indirectly, when some other parameter associated with the signal is detected.

eg. electrodes (used for the detection of electric currents or voltages)

32
Q

What are the different types of electrodes used for biomedical purposes?

A

1) MICROELECTRODES: used for measuring the potential inside one cell. (conducting small wire, inserted into a glass pipette willed with electrolyte solution, tip of pipette is open).
2) SMALL METAL WIRES: record summery potentials of many cells under the tip of wire.
3) LARGE METAL ELECTRODES: used for ECG recording

33
Q

What does “noise” refer to in biosignals?

A

signals which interfere with the signal of interest.

34
Q

State examples of noise.

A

Noise can be originated from both internal and external sources.
- running devises (sensors, amplifiers)
- electromagnetic interferences (powerlines, nearby operating electric equipment)
- other signals appearing in the organism, however not related to the recording of the signal.

35
Q

How can one “clean” a recorded signal from noise?

A
  • differential amplifier
  • grounding
  • electrostatic shield
  • filtering
36
Q

What is a differential amplifier?

A

An electronic device with two inputs for voltage (V1 and V2), and one output (Vout).

output voltage = V2-V1 (input voltage difference)

By connecting electrodes to two different inputs of a differential amplifier, both electrodes will have equal potentials, so V1 = V2, and the potential at output induced by noise = 0.

37
Q

Explain grounding. What physical property of the body is employed

A
  • capacitance is employed
  • external fields cannot change the electrical potential of the physical body if the body has a very high electric capacitance.

by connecting a metal wire, external electrical fields (sources of noise) will have less influence on the electric properties of the body.

38
Q

Why is the Earths potential considered to be constant?

A

Because the Earth has a very high capacitance.

39
Q

What is electrostatic shielding? What is another word for it?

A

If one positions the biological object inside a system with zero electric field inside and surrounding it, then noise is reduced.
This is called the Faraday cage.

40
Q

What is the total electric field inside an electric conductor?

A

zero

41
Q

What is the total electric field of the space surrounding an electric conductor?

A

zero

42
Q

Explain the Faraday cage. What is the main principle?

A

A Faraday cage works based on the principle of electromagnetic shielding. When an external electrical field is applied to the cage, positive charges are fixed and free electrons are redistributed along the conductive materials due to electrostatic induction.

43
Q

What can “filters” do?

A

Filters can abolish signals of some particular frequencies and conduct other frequency signals.

44
Q

What are the different types of filters?

A

Low pass (LPF)
High pass (HPF)
Band pass (BPF)

45
Q

When can one use a filter to clean noise?

A

if the frequencies of the recording signals and noises are different

46
Q

What filter is used when the frequency of the noise is higher than the frequency of the recording signal?

A

lowpass filter

47
Q

What filter is used when the frequency of the noise is lower than the frequency of the recording signal?

A

highpass filter

48
Q

What type of signals do bandpass filters conduct?

A

signals inside a certain range of frequencies.

49
Q

What are the units of amplitude?

A

meters

50
Q

What is the symbol for amplitude?

A

A

51
Q

What is the unit of frequency?

A

Hertz (Hz)

52
Q

What is 1 Hertz equal to?

A

1 cycle per second (1/sec)

53
Q

What are the units of electrical potential?

A

Volts

54
Q

What is 1 Volt equal to?

A

1 J/C

55
Q

What is the Joule a measure of?

A

the work done by a force one newton acting through one meter.
energy

56
Q

What does the Coulomb measure?

A

the quantity of electricity transported in 1 second by a current of one ampere.

Medical Physics (8 decks)

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