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Lecture 1.1. Flashcards

1
Q

What have been the driving factors of technology development?

A
  1. Understanding the body
  2. Anaesthesia
  3. Electro magnetic spectrum
  4. Ionising radiation
  5. Understanding electricity
  6. Electronic control
  7. Digital electronics
  8. Micro processors
  9. Broadband and wireless connectivity
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2
Q

What are the applications of technology?

A

Diagnosis - measurements of in vitro + in vivo
Treatment
Life support
Monitoring

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3
Q

Define in vivo and in vitro

A

In vitro- from sample
In vivo - on patient

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4
Q

Define a transducer, what is it used for?

A

Used to transform one form of energy to another
Often disposable (single use) to reduce risk of infection

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5
Q

Give examples of clinical transducers

A

SPO2
incline BP

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6
Q

What are the requirements of transducers?

A

Stable, Repeatable, Bio-compatible, Affordable, able to Disinfect/Sterile

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7
Q

Name some parameter which may need/want to measure

A

Temperature
Oxygen
Light intensity
Pressure

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8
Q

What generally is the output signal after measuring from parameters?

A

An electrical signal for digital processing to a digital or graphic display

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9
Q

What does false positive and false negative mean?
What are the consequences of each?

A

False negative: shows not present when actually is present
Consequence: missed diagnosis, late treatment

False positive: shows present when actually not present
Consequence: unnecessary treatment or intervention, needless worry

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10
Q

What does sensitivity and specificity represent?

A

Evaluation of diagnostic tests

Specificity: Measure used to assess the effectiveness of a diagnostic testing correctly identifying people who do not have a particular disease, without disease. Good at identifying healthy people
TNR
Cases detected / actual number of cases
True positive/ true positive + false negative

Sensitivity: opposite, good at identifying positive cases (sick people)
TPR
Number found clear / actual number of disease free
True negative / true negative + true positive

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11
Q

What are the effects of good sensitivity? Why is it needed also? What are the effects of false negatives?

A

Needed for screening

False negatives mean missing disease, delaying treatment, risking spread

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12
Q

What are the effects of poor specificity? What do false positives case?

A

False positives cause over reporting, may lead to unnecessary intervention

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13
Q

What do lateral flow COVID tests show regarding specificity and sensitivity ?

A

Specificity is High

Sensitivity high for viral loads, but not high for lower levels so PCR test is needed

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14
Q

Define invasive and non invasive with respect
Give examples

A

Invasive - in the body, allows you to see directly what’s going on
Most accurate and direct
Core temp, cardiac output

Non invasive - does not penetrate the skin

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15
Q

What are the disadvantages of invasive medical devices?

A

Can cause injury
Need to heal
Risk infection
Thrombosis
Can be uncomfortable or painful

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16
Q

How can one minimise invasive techniques?

A

Taking advantage if the patient needs opening , can use the same access port for measuring (cardiac output)

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17
Q

What type of techniques are used during minimal invasive surgery?

A

Laparoscopy techniques

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18
Q

Using pre-existing access, intracavity techniques are used, what surgeries/devices can be involved in this?

A

Rectal and vaginal scanning

Ear and nasopharyngeal thermometers

Endoscopy

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19
Q

Are light sources transducers? If so, why?

A

Yes

They convert electrical energy to optical (EM radiation)

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20
Q

Name light sources

A

LEDs
Filament lamps, latterly filled with halogen
Gas discharge, including fluorescent tubes
LASERs with various base materials

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21
Q

What are the factors to consider when choosing a light sources?

A

Power output required
Wavelength (colour)
Bandwidth (spread/mix of wavelength)
Coherent length (consistency)

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22
Q

What is the range of the visible spectrum?

A

390 to 700nm of the EM spectrum

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23
Q

What light source device has a long coherent length?

A

LASER

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24
Q

Define the bandwidth with respect to light source devices.

A

The difference in frequency between half peak values of the spectrum (FWHM)

25
What does FWHM stand for?
Full width at half maximum
26
Define coherent length
Length over which the light stays in constant phase
27
Give the speed of propagation formula
C = wavelength x frequency
28
Tell about the tungsten filament lamp
Primary source of illumination for a century When an electric field is passed through the filament, it heats up and emits light. The filament is protected by an inert gas in a glass envelope
29
What does inert mean?
Something that doesn’t reach or change easily with other substances
30
Tell about halogen filament lamps
Developed in the middle of the last century Uses halogen as the gas Durable, more efficient and compact Allows filament to run hotter while being more durable Still widespread use - endoscopic work, connected to fibre optic cable to guide light down the endoscope Note that glass envelope should not be touched, fingerprints left on the cause premature failure
31
What is population inversion with respect to LASERs
Normally, elements and compounds have more electrons in higher shells compared to lower shells, but here it is actually more electrons in higher shells compared to lower shells?
32
What does LASER stand for?
Light Amplification by Stimulated Emission of Radiation
33
Explain how a LASER works
Pumping atoms: a light source adds energy to atoms, moving them to a higher energy level Population inversion: more atoms end up in these higher energy levels than the lower ones, which is the ‘inverted’ state needed for LASERs Mirrors: the lasing material (the substance that produces light) is placed between two mirrors. When an atom drops back down to their lower energy level, they release light (photon) Reflection: the light bounces back and forth between the mirrors. Each time it bounces, it can cause other atoms to release more light, and they all stay in sync (in phase) Output: One of the mirrors is semi-reflective, allowing some of the light to escape as the laser beam
34
Describe the resultant beam from the LASER
highly parallel and coherent Spatially (tight and well focused) and temporally (consistent and stable) Space and time
35
What is the advantage of having highly parallel and coherent lasers?
Enables high intensities and using in surgery
36
Who can use the LASERs? Where?
Trained staff under strictly approved operating procedures Must be used with great care
37
What is is the more powerful LASER - solid state or surgical?
Surgical
38
When are solid state LASERs used? And why?
Physiological measurements , Compact LED lasers Less dangerous but not completely safe
39
How does a LED work?
PN junction: made up by joining two types of semiconductors, one with extra electrons and one with extra holes. Forward bias: when electricity is applied in the right direction, electrons move across the junction to the p side Energy release: as electrons move to the p side, they drop down to a lower energy state and release energy in the form of light (photons) Wavelength and colour: the energy released and therefore colour depends on the type of semi conductor and how it is doped. Structure and nature, this sets the wavelength
40
What is more efficient, LEDs or light bulbs? Give the reason
LEDs, they waste less energy as heat, making them ideal for applications like medical devices, where heat could be a problem
41
What does the frequency of the photon depend on for a LED? Give the formulas involved
Band gap E=hf c= wavelength x f Wavelength = hc/E
42
What type of light did the first LEDs produce? What colours were available only? What were the commonly used for ?
Infrared Red and green Indicators
43
What colour of LED light was invented that was a major breakthrough? And what did it allow to happen?
Blue Allowed the creation of white light by combing with red and green, this also made the light much more efficient. Combine colours to create different light colours Use of a phosphor layer or combining colours , emitted spectrum can be changed Phosphor layer absorbs light at one wavelength and re-admits it at a different one Addition of blue LEDs helped create more efficient and versatile lighting by allowing for better colour mixing and new techniques
44
How does gas discharge work?
Emit light by passing a current through a noble gas (argon, neon, krypton) at low pressure Generally also contain mercury, sodium or a metal halide Atoms accelerated by the field collide with atoms in the gas which excites them to higher energy states As they drop back down to the ground state the gas electrons give of photon linked to their energy wavelength
45
How does fluorescent lighting work?
Fluorescent phosphor used to coat the lamp and emit white light Used in some applications
46
Why is the fluorescent lighting technique particularly useful in lab instruments?
These lights give intense light of distinct wavelengths
47
What is used to measure light intensity?
Photodiode
48
How does a photodiode work?
PN Junction: made from a doped semiconductor. Reverse bias: the photodiode is connected to a power supply in reverse bias. This means the voltage is applied in a way that normally prevents current from flowing (blocking the flow of electricity through the device) Absorbing light: when light hits the photodiode, it excites the electrons in the semiconductor material. This energy allows some of the electrons in the material to overcome the reverse bias and cross the junction from p to n side Current flow: as a result, a small current starts to flow across the diode. The amount of current depends on how much light the photo diode absorbs. More light = more current. Measuring the current that flows through the photodiode can be measured, and it gives an indication of the intensity of the light that hit the photodiode. Simple terms: works by using reverse bias to block normal current flow, but when light hits it, it generate a small current that can be measured. This current tells you how much light is absorbed
49
What are the two main reasons for batteries?
To make equipment portable To compensate for electrical mains failure
50
Why would transportable equipment need batteries? Four reasons
Need to last through transport to the hospital Ambulances generally don’t have built in supplies Need to work first time, every time - suction, defib If the electrical mains fail, the battery can carry through until backup supply is found
51
What are the risks associated with batteries?
Overcharging can be dangerous, especially with lithium Leakage can damage equipment - particularly lead acid but most of these are now gel filled Short circuits can cause high current flow - a risk of poor battery container
52
When selecting a battery, what are the considerations?
Battery capacity - adequate, reduce with age/use? Charge leakage - maintain charge? Well designed?
53
Name the battery types
Lead acid, nickel cadmium, nickel metal hydride, lithium ion
54
Why are modern batteries filled with gel?
To prevent spillage and evaporation and make them maintenance free Termed ‘sealed lead acid’ although they do have venting
55
What are the advantages and disadvantages of lead acid batteries?
Advantages - high current capability - low self discharge Disadvantages - do not like deep discharge - heavy -low energy density -environmentally unfriendly -likes slow charge -short life cycle
56
What are the advantages and disadvantages of nickel cadmium batteries?
Advantages -can be charged quickly -can be deep discharged -high cycle lifetime -long shelf life -comparatively low cost Disadvantages -should not be left on trickle charge -need exercised -low energy density -environmentally unfriendly -high self discharge Disadvantages
57
What are the advantages and disadvantages of nickel cadmium metal hydride batteries?
Advantages -higher energy density -environmentally friendly Disadvantages -no deep discharge -no toleration of high currents -Requires regulated charge -needs cycled -high self discharge Disadvantages
58
What are the advantages and disadvantages of lithium ion batteries?
Advantages -high energy density -low discharge rate -no memory effect Disadvantages - cost -environmental impact, both in production and disposal -limited shelf and cycle lifetime, capacity reduces -moderate current capacity -transport restrictions
59
What are the precautions to know and take when dealing with battery powered equipment?
Generally left on charge Scheduled battery changes must be recorded at programmed intervals (by age or use) Only correct, suitable chargers used

Medical Devices (2 decks)

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