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Bioinstrumentation > Chapter 1: Basic concepts of medical instruments > Flashcards

Chapter 1: Basic concepts of medical instruments Flashcards

1
Q

Describe the generalize instrumentation system

A
  • Sensor converts info from measurand
  • Signal created is processed and displayed
  • Info is perceived
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2
Q

Measurand

A

physical quantity, property, or condition that the system measures.

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3
Q

Give examples of medical measurands

A

biopotential, pressure, flow, dimensions, displacement, impedance, temperature, chemical concentration

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4
Q

Sensor

A
  • aka Transducer
  • Sensors convert physical measurand to an electric output
  • Must only respond to specific measurand and exclude all others
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5
Q

Describe how a sensor should interact with a living system

A
  • must minimize energy extracted

- must be minimally invasive

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6
Q

Signal Conditioning

A

Since sensor output cannot be directly displayed, signals must be conditioned.

  • amplified
  • Filtered
  • Conversion to other signal types (like digital)
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7
Q

Output Display

A
  • Results of a measurement process must be displayed that is perceivable.
  • Form of display depends on presentation desired, particular measurand, and how info will be used.
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8
Q

Auxiliary Elements

A
  • data transmission
  • calibrations
  • data storage
  • control
  • feedback
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9
Q

Calibration signal

A

-Should be applied to sensor input as early in signal-processing chain as possible.

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10
Q

Direct-Indirect Modes

A

When desired measurand isn’t accessible, another measurand that is related to the desired one can be used to generate a new measurand.

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11
Q

Give an example of a direct-indirect mode

A

Cardiac output (volume of blood pumped per minute by the heart) is determined by measurements of respiration and blood gas concentration/ or from dye dilutions

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12
Q

Sampling and Continuous Modes

A
  • Measurements that change very slowly may be sampled infrequently (like body temperature)
  • Measurements may require continuous monitoring (like respiratory gas flow)
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13
Q

Generating Sensors

A

Produce their signal output from energy taken directly from the measureand

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14
Q

Modulating Sensors

A

Use the measurand to alter the flow of energy from an external source in a way that affects the output of the sensor

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15
Q

Analog Signal

A
  • signal that is continuous and able to take on any value within the dynamic range.
  • most signals operate in this mode
  • require calibration often
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16
Q

Digital Signal. List advantages/disadvantages

A
  • signal is able to take on only a finite number of different values.
  • advantages: greater accuracy, repeatability, reliability, immunity to noise, periodic calibrations not required as often
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17
Q

Biomedical instrumentation Classifications

A
  • quantity that is sensed
  • principle of transduction
  • organ system
  • clinical medicine specialties
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18
Q

Desired inputs

A

measurands that the instrument is designed to isolate

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19
Q

Interfering inputs

A

quantities that inadvertently affect the instrument as a consequence of the principles used to acquire and process the desired inputs.

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20
Q

Modifying inputs

A

undesired quantities that indirectly affect the output by altering the performance of the instrument itself

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21
Q

Give example of two possibly interfering inputs

A
  1. stray magnetic fields

2. capacitively coupled noise

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22
Q

Give example of two possible modifying inputs

A
  1. orientation of patient cables

2. changes in electrode-skin impedance

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23
Q

How can most interfering and modifying inputs be reduced or eliminated?

A

-altering design of essential instrument components or by adding new components designed to offset the undesired inputs

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24
Q

transducer

A

converts a signal from one form of energy to another

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25
Q

What are two types of sensor mechanics?

A
  1. direct

2. indirect

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26
Q

What are 2 types of signal conversion?

A
  1. Single

2. Dynamic

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27
Q

What types of signal measurement?

A
  1. static
  2. Dynamic
  3. Pulsed
    & additionally invasive or non-invasive
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28
Q

Direct sensor measurement

A

measure value is proportional to an electrical signal

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29
Q

Indirect sensor measurement

A

-derive the final measurement by solving the mathematical governing equations for the system and the sensor

30
Q

Draw schematic of multiple conversion sensor and give an example.

A

physiological variable->intermediate variable->sensor->electrical signal.
example) serum glucose>hydrogen peroxide>H2O2 sensor>electrical signal

31
Q

Draw schematic of single conversion sensor and give an example

A

physiological variable>sensor>electrical signal

example) body temp>thermistor>electrical resistance

32
Q

static signals

A

change very little with time. can be approximated as a zero order system

33
Q

dynamic signals

A

result in a significant change with time

34
Q

Pulse signals

A

periodic with time. Usually like to count the pulses and correlated with the phenomena

35
Q

Resolution

A

The smallest incremental quantity that can be measured with certainty

36
Q

Reproducability

A

the ability of an instrument to give the same output for equal inputs applied over some period of time

37
Q

Biological signals

A
  • generally dynamic and stochasitic in nature

- difficult to measure because they undergo very discrete changes and there is much interferance

38
Q

Accuracy

A
  • Average closer to “true” value
  • The difference between the true value and the measured value divided by the true value.
  • Expressed as percentage of reading
39
Q

Precision

A
  • “Repeatibility”

- A measurement that expresses the number of distiguishable alternatives from which a given result is selected

40
Q

Sensitivity

A
  • An absolute quantity used in analog instruments

- smallest absolute amount of change that can be detected by a measurement

41
Q

Resolution

A

The smallest incremental quantity that can be distinguished with certainty-usually A/D

42
Q

Types of Instrument error

A
  1. Systematic/bias

2. Random

43
Q

Systematic/bias error

A

can be removed by calibration

44
Q

Random errors

A

can be removed by taking multiple measurements and averaging the results

45
Q

What is the acceptable error?

A
  • depends on the application
  • high accuracy/precision generally means high cost
  • anticipate the future (make higher quality stuff)
46
Q

Give 4 examples of physical sensors

A
  1. Strain gauge/load cell
  2. Flow sensor
  3. Thermistor
  4. Pressure sensor
  5. Metal resistance thermometer (RTD)
47
Q

Give 2 examples of bioanalytical sensors

A
  1. Glucose sensor

2. Lactate sensor

48
Q

Give 4 examples of chemical sensors

A
  1. oxygen electrode
  2. glass electrode
  3. ion-selective electrode
  4. CO2 sensor
49
Q

Actuator

A

A device that converts an electric signal to a physical output

50
Q

Resistor sensor

A
  • Converts the measurand to electric signal by changing its resistance
  • Deformation of the sensor material is common mechanism to change the resistance
  • such as strain gage
51
Q

Conductance

A

(1/resistance)

52
Q

Strain gage

A
  • aka load cell

- a device whose electrical resistance varies in proportion to the amount of strain applied on the device

53
Q

Wheatstone Bridge

A
  • a circuit that is typically used to detect the resistance change of the resistor sensor
  • contain four resistors arranged in a diamond
54
Q

Linear Variable Differential Transformer

A
  • LVDT
  • when core is in null position (the center) the output voltage is zero.
  • when core moves up the secondary coil gets more flux and so has larger voltage.
55
Q

Capacitive Sensor

A

capacitance between two parallel plates of area A separated by distance x
-possible to measure displacement by altering either A or x

56
Q

Piezoelectric Sensor

A
  • an electric charge generator with high impedance and a small intrinsic capacitor
  • requires a charge amplifier to amplify the electric signal from the piezoelectric sensor.
  • amplifier must have extremly high input impedance to avoid extracting too much energy from sensor
57
Q

Thermocouple

A
  • based on discovery that electromotive force (emf) exists across a junction of two dissimilar metals
  • two effects
  • 1st effect: due to contact of two unlike metals and the junction temp
  • 2nd effect: due to temp gradient along each single conductor
  • one junction in water and icebath at zero temp
  • other junction for temp measurement
58
Q

Thermistor

A
  • semiconductor made of cermaic materials that are thermal resistors with high negative temp coefficient.
  • high resistance
  • typically used for very high temperatures
59
Q

RTD

A

Resistance temperature detectors

  • made of coils or films or metals (usually platinum)
  • resistance of metal increases when heated and decreases when cooled.
  • very accurate
  • very stable
  • low resistance
  • typically use an OpAmp type of circuit
60
Q

Photoelectric optical sensors

A
  • photo-emissive sensors
  • photoconductive sensors (LDRs)
  • photovoltaic sensors
61
Q

Absorption/flourescence Optical sensors

A

-different dyes show peaks of different values at different concentrations when absorbance is plotted against wavelength

62
Q

Phenol Red

A
  • an optical sensor through absorbance

- a pH sensitive reversible dye whole relative absorbance is used to measure pH

63
Q

HPTS

A

-an irreversable fluorescent dye used to measure pH

64
Q

Direct Optical Biosensor

A
  • detects changes in light intensity and signifies changes in measurant like mass or concentration
  • ex: pulse or blood level
65
Q

Fiber Optics

A
  • amount of light transmitted is proportional to temperature
  • sensor is extremely sensitive
  • Most of light is trapped in the core
  • if cladding is temperature sensitive, it might allow some light to leak through.
66
Q

Pulse oximetry

A
  • a spectrophotometric device
  • detects and calculates differential absorption of light by oxygenated and reduced hemoglobin to ger sO2.
  • two light sources and a photodetector
67
Q

Potentiometric sensor

A
  • an electrochemical sensor
  • involve measurement of emf of a cell at zero current.
  • proportional to the log of the concentration of the substance being determined
68
Q

Amperometric Sensor

A
  • an increasing/decreasing potential is applied to the cell until oxidation/reduction of the substance to be analyzed occurs and there is a sharp rise/fall in the current to give a peak current.
  • peak current= concentration of electroactive material
69
Q

Conductometric sensor

A
  • an electrochemical sensor

- Normally results in a change in the electrical conductivity of the solution, which can be measured electrically

70
Q

Chemical Biosensors

A

-produce an electrical output which is proportional to the concentration of biological analytes

71
Q

pO2 electrode

A
  • clark electrode
  • cathode is a noble metal
  • Dissolved O2 diffuses from the blood and is reduced
  • voltage kept constant
  • current is produced and measured directly
72
Q

Describe the twisted wires technique

A

d

Bioinstrumentation (1 decks)

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