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Further Additional Physics > Topic 1 - Radiation and Treatment > Flashcards

Topic 1 - Radiation and Treatment Flashcards

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1
Q

How can X-rays be used in medical imaging?

A
  • High energy EM waves, absorbed by dense materials (e.g. bone, metal)
  • Radiographers: use these properties for photographs for diagnoses e.g. bone fractures
  • Ionising radiation so health risk
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2
Q

How can X-rays be used in CAT scanning?

A
  • CAT, computerised axial tomography
  • Use X-rays to produce 2D slice through body
  • Use intense beams of X-rays that are strongly ionising
  • Can image soft tissue, not just bones
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3
Q

How do endoscopes work?

A
  • Use visible light, not ionising
  • Reflect light along optical fibres
  • See inside patient to investigate problems without invasive surgery
  • Can be used for keyhole surgery
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4
Q

What are the three ways ultrasound can be used medically?

A
  • Breaking down kidney stones
  • Pre-natal scanning of a foetus
  • Measuring speed of blood flow
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5
Q

What is ultrasound?

A
  • Sound waves with frequencies above 20kHz, above range of human hearing
  • Non-ionising so safer than ionising
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6
Q

How is ultrasound used to break down kidney stones?

A
  • Kidney stones: hard masses that can block urinary tract, painful
  • Ultrasound beam concentrates high energy waves at kidney stone
  • Turns it into sand like particles
  • Pass out patient’s body in urine
  • No surgery and relatively painless
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7
Q

How is ultrasound used in pre-natal scanning of a foetus?

A
  • Ultrasound imaging: diagnose soft tissue problems and perform pre-natal scans of foetus in womb
  • U.sound waves reflected off the different tissue boundaries
  • Times/distributions of echoes processed by computer to form image on a screen
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8
Q

How is ultrasound used in measuring the speed of blood flow?

A
  • Works in real time
  • Can show things moving/changing
  • Can investigate blood flow, particularly in heart/liver
  • Can measure the speed of blood flow by special u.sound machines
  • Can identify blockages in veins/arteries
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9
Q

What is radiation?

A

Energy emitted from a source

Can be in the form of a wave or particle

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10
Q

What two factors affect the intensity of radiation?

A
  • Distance from source

- What it’s passing through: some radiation absorbed by medium passing through (unless in vacuum)

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11
Q

What is the general rule of how much radiation is absorbed by a medium it passes through?

A

Denser mediums absorb more energy, so decrease intensity more

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12
Q

If radiation has a greater intensity, what must also be greater?

A

More energy it carries per second or higher power (higher power=more energy transferred per second when hits an object)

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13
Q

How does surface area affect the amount of radiation it absorbs?

A

Greater surface area means more radiation hits it, so catches more

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14
Q

What is the equation for intensity?

A

Intensity=power/area

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15
Q

What is intensity measured in?

A

W/m^2

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16
Q

What is refraction?

A

When radiation changes direction as it enters a different medium

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17
Q

What causes refraction?

A

The change in density from one medium to another, therefore changing the speed

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18
Q

How does radiation refract when it slows down?

A

Bends towards the normal

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19
Q

What happens if radiation hits a boundary at 90⁰?

A

Does not change direction but does slow down

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20
Q

What happens to a light when it hits a different medium?

A

Some light reflected, and some will pass through (refraction), depending on the angle of incidence, i

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21
Q

What are the two main types of lenses?

A

Converging and diverging

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22
Q

What shape is a converging lens and how does it affect the light?

A
  • Convex

- Cause parallel rays to converge (move together) to focus at the lens focal point, F

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23
Q

What shape is a diverging lens and how does it affect the light?

A
  • Concave (caves inwards causing parallel rays to diverge [spread out])
  • Focal point is point where rays hitting the lens parallel to the axis appear to come from, trace them back until they all meet up at point behind the lens
  • Focal length: distance between middle of lens and focal point
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24
Q

What are the three rules for refraction in a converging lens?

A
  • An incident ray parallel to the axis refracts through the lens and passes through the focal point on the other side
  • An incident ray passing through the focal point before entering the lens will refract through the lens and travel parallel to the axis
  • An incident ray passing through the centre of the lens carries on in the same direction
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25
Q

What are the three rules for refraction in a diverging lens?

A
  • An incident ray parallel to the axis refracts through the len, and travels in line with the focal point (so it appears to have come from the focal point)
  • An incident ray passing towards the focal point refract through the lens and travels and parallel to the axis
  • An incident ray passing through the centre of the lens carries on in the same direction
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26
Q

What type of image does a diverging lens always create?

A

Virtual

Right way up, smaller than object on same side of lens, despite object location

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27
Q

What is the correlation between power and focal length?

A

The more powerful the lens, the more strongly it converges, so shorter focal length

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28
Q

What is the equation for the power of a lens?

A

Power of lens = 1 / focal length

29
Q

What is the difference between the power of a converging lens and the power of a diverging lens?

A

A converging lens’ power is always positive, a diverging lens’ power is always negative

30
Q

In the equation 1/f=(1/u)+(1/v), what do f, u and v represent?

A

f=focal length
u=object distance
v=image distance

31
Q

What is the equation to show the relationship between the position of the object, position of the image and the focal length?

A

1/f=(1/u)+(1/v)

32
Q

In the equation 1/f=(1/u)+(1/v), what does it mean if v is positive/negative?

A
  • Positive: real image

- Negative: virtual image

33
Q

What is the iris and what is its function?

A
  • Coloured part of the eye
  • Made of muscles controlling size of pupil (hole in middle of iris)
  • Controls the amount of light entering the eye
34
Q

What is the cornea and what is its function?

A
  • Transparent ‘window’ with a convex shape

- Focuses the light

35
Q

How do the lens and the cornea work together to focus light to retina?

A
  • Cornea has fixed power

- Lens can change focusing power by changing shape

36
Q

What are the ciliary muscles and what are their function?

A
  • Control the lens
  • When contract, lens has fat, spherical shape
  • When relax, lens become thin, flatter shape
37
Q

What is the retina and what is its function?

A
  • Covered in light sensitive cells

- Detect light and send signals to brain via the optic nerve

38
Q

What is the far point of an eye?

A

The furthest distance the eye can focus comfortably

39
Q

If you have normal sight, what is the far point and near point of your eye?

A

infinity

around 25cm

40
Q

What is the near point of an eye?

A

The closest distance that the eye can focus on

41
Q

What does it mean if you are short sighted?

A
  • Can’t focus on things far away (far point is closer than infinity)
  • Images of distant object brought into focus in front of retina
42
Q

What can cause short sightedness?

A
  • Cornea and lens aren’t powerful enough
  • Eyeball is too long
  • Ciliary muscles are unable to relax enough to change the shape of the lens to focus the light on the retina
43
Q

What does it mean if you are long sighted?

A
  • Can’t focus clearly on near objects

- Near point is further than normal (25cm+)

44
Q

What can cause long sightedness?

A
  • Cornea and lens too weak
  • Eyeball is too short
  • Ciliary muscles not able to contract enough to change the shape of lens to focus light on the retina
45
Q

Why do lots of people become long sighted as they get older?

A

Eye lens becomes stiffer or ciliary muscles become weaker so eye loses some focussing power

46
Q

How can short sightedness be corrected?

A
  • Glasses with diverging lenses
  • Correcting lens must have focal point at eye’s fault far point
  • Means objects at infinity, which were out of focus, now seem to be in focus at the far point
47
Q

How can long sightedness be corrected?

A
  • Glasses with converging lenses
  • Converging lens used to produce virtual image of objects 25cm away at eye’s near point
  • Close objects which were out of focus now seem in focus at near point
48
Q

How can contact lenses be used to correct vision?

A
  • Cornea does most of eye’s focussing
  • When wrong shape can be too weak/powerful (responsible for long and short sight)
  • Contacts sit on top of cornea
  • Shaped to compensate for fault
  • Can be converging or diverging
49
Q

How can laser eye surgery be used to correct vision?

A
  • Vaporise tissue, changing cornea’s shape
  • Slimming it: less powerful, improving short sight
  • Changing so more powerful, improving long sight
  • Surgeon can precisely control amount of tissue removed
50
Q

What are the advantages and disadvantages of using glasses to correct vision?

A

+Can be cheapest
+Can even treat severe eye lenses as can be very thick
+Can be adjusted to correct vision changes
-Often heavy and uncomfortable
-Not the best looking

51
Q

What are the advantages and disadvantages of using contact lenses to correct vision?

A 
\+Convenient
\+Relatively cheap
\+Lightweight
\+Almost invisible
\+Can be adjusted to correct vision changes
-Uncomfortable
-Can fall out of eye
-Can get eye infections if not looked after properly
52
Q

What are the advantages and disadvantages of using laser eye surgery to correct vision?

A

+Easier than having to wear contacts/glasses

  • Expensive
  • Risk of complications e.g. infection, eye responding to make vision worse
  • Can not be adjusted to correct vision changes
53
Q

What affects the amount of light refracted?

A

Refractive index

54
Q

What is the refractive index of:
air?
water?
glass?

A

1

  1. 33
  2. 5
55
Q

What is the equation relating angle of incidence, angle of refraction and refractive index?

A

n=(sin i)/(sin r)

56
Q

In the equation n=(sin 1)/(sin r), what does i, r and n represent?

A

i=angle of incidence
r=angle of refraction
n=refractive index

57
Q

What happens to the light passing out of a glass prism if the angle of incidence is less than the critical angle?

A

Most light passes out but a little bit is internally refelcted

58
Q

What happens to the light passing out of a glass prism if the angle of incidence if equal to the critical angle?

A

The emerging rays come out along the surface. Quite a bit of internal reflection

59
Q

What happens to the light passing out of a glass prism if the angle of incidence is greater than the critical angle?

A

No light comes out, all internally reflected, total internal reflection

60
Q

What is TIR (total internal reflection)?

A

When not light passes out of a prism and it is all reflected

61
Q

What is the equation to work out the critical angle?

A

sin C=n~r / n~i

62
Q

In the equation sin C=n~r / n~i, what do n~r and n~i represent?

A

n~r=refractive index of stuff light is travelling towards

n~i=refractive index of stuff light is travelling from

63
Q

What is the correlation between refractive index and critical angle?

A

The higher the refractive index, the lower the critical angle

64
Q

What can optical fibres be used for?

A

Medical diagnosis and communications technology

65
Q

How do optical fibres work?

A
  • Total internal reflection
  • Light waves reflect off side of thin inner core of plastic/glass
  • Wave enters one end of fibre and is reflected repeatedly until it emerges at the other end
  • Fibre must be narrow enough to keep angles above the critical angle + fibre mustn’t be bent too sharply
66
Q

What is an endoscope?

A

A thing tube containing optical fibres that lets surgeons examine inside the body

67
Q

What is an endoscope made up of?

A

Consist of 2 bundles of optical fibres: one to carry light to area of interest, one to bring image back for viewing

68
Q

How can the image from an endoscope be viewed?

A

Through and eyepiece or displayed as full colour moving image on TV screen

69
Q

What is the big advantage of using endoscopes?

A

Can now do keyhole surgery (only making very small holes in the body) which couldn’t be done before optical fibres

Further Additional Physics (5 decks)

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