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Physics Michael > P3.1 Medical Applications of Physics Part One > Flashcards

P3.1 Medical Applications of Physics Part One Flashcards

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1
Q

What are X-rays?

A

High frequency, short wavelength electromagnetic waves

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2
Q

How big is the wavelength of a X-ray?

A

Roughly the same size as the diameter of an atom

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3
Q

Are X-rays ionising radiation? What does this mean?

A

Yes, this means they can damage or even kill living cells

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4
Q

What happens when X-rays are directed at a human body?

A

They pass through body tissue, and absorbed by denser materials like bones and metal

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5
Q

How do X-rays affect photographic film? What does this mean they can be used for?

A

The same way as light, meaning they can be used to take photographs in which body parts, like bones, can be seen

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6
Q

What can X-ray photographs be used for?

A

To diagnose medical conditions such as bone fractures or dental problems

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7
Q

How are X-ray images formed nowadays?

A

Electronically using charge-coupled devices (CCDs)

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8
Q

What are CCDs?

A

Silicon chips that are divided up into a grid of millions of identical pixels

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9
Q

How do CCDs form an image from X-rays? What is quality of these images?

A

They detect X-rays and produce electronic signals which are used to form high resolution images (the same technology in digital cameras)

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10
Q

Can X-rays be used to take photos of tissue? Why? How?

A

Yes, tissue can absorb small amounts of X-ray radiation, so Computerised axial tomography can be used to produce images of soft and hard body tissue

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11
Q

What does CT scans mean?

A

Computerised axial tomography

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12
Q

What is the quality of the images produced from CT scans?

A

They produce high-resolution images

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13
Q

How does the dosage of X-rays change from CT scans and normal X-ray photographs?

A

CT scan use a high dose of X-rays in order to distinguish between the tiny variations in tissue density

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14
Q

How are CT scans carried out?

A

A patient is put inside a cylindrical scanner, and an X-rays beam is fired through the body from an X-ray tube to a detectors

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15
Q

Where does a CT scan take place?

A

In a cylindrical scanner

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16
Q

What happens to the X-ray tubes and detectors in a CT scan?

A

They are rotating during the scan

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17
Q

How are the images formed from a CT scan?

A

A computer interprets the signals from the detectors to form an image of a 2D slice through your body

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18
Q

How are 3D images formed from a CT scan?

A

Multiple 2D CT scans can be put together to make a 3D image

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19
Q

What does the high quality images produced from a CT scan allow doctors to do? (3)

A

Diagnose things such tumours, organ disease, blood flow issues and bone fractures

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20
Q

Why are CT scans sometimes avoided?

A

Because they involve a lot more exposure to X-rays than taking an X-ray photograph

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21
Q

What can X-rays be used for besides photographs?

A

Radiotherapy

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22
Q

What is radiotherapy?

A

The treatment of cancers with X-rays

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23
Q

How is radiotherapy carried out? (3 steps)

A
  1. X-rays are focused on the tumour using a wide beam
  2. This beams is rotated round the patient with the tumour at the centre
  3. This minimises the exposure of normal cells to radiation, and so reduces the chances of damaging the rest of the body
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24
Q

What are the safety measure when using X-rays? (2)

A

The radiographers carrying out the radiotherapy wear lead aprons and stand behind lead screens, and the X-ray exposure of the patient is always kept at a minimum

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25
Q

What are the results of prolonged exposure to ionising radiation? (3)

A

Cancer, radiation sickness and death

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26
Q

Why do radiographers wear lead aprons?

A

Because lead absorbs X-rays

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27
Q

What is ultrasound?

A

Sound waves of a higher frequency than the upper limit of human hearing

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28
Q

What is the range of human hearing?

A

20 to 20,000 Hz

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29
Q

What is partial reflection?

A

When a wave passes from one medium into another, some of the wave reflects off the boundary between the two media and some is transmitted (and refracted)

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30
Q

What is meant by ‘transmitted’ in waves?

A

Passes through

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31
Q

What does partial reflection allow ultrasound to be used as?

A

Ultrasound imaging

32
Q

How does ultrasound imaging work?

A

A pulse of an ultrasound is pointed at an object, wherever there are boundaries some of the ultrasound will be reflected - knowing how fast the ultrasound is travelling, then the time it takes for the reflections to reach a detector can be used to calculate how far away the boundary is

33
Q

What does the ultrasound detector receive?

A

Partially reflected ultrasound

34
Q

What can you use to measure the time between reflected pulses in an ultrasound?

A

You can use oscilloscope traces from an ultrasound detector

35
Q

How do you find the time between pulses in an oscilloscope?

A

You multiply the number of divisions (squares) by the timebase

36
Q

What formula do you use to work out the distance between boundaries in an ultrasound?

A

s = v x t ==> distance in m = speed in m/s x time in s

37
Q

What are kidney stones?

A

Hard masses that can block the urinary tract

38
Q

How does an ultrasound remove kidney stones?

A

An ultrasound beam can be used to concentrate high-energy waves at the kidney stone, turning it into sand like particles

39
Q

What is the main use of an ultrasound?

A

Pre-natal scanning

40
Q

Why are ultrasounds used in pre-natal scanning’s?

A

Because ultrasound waves are non-ionising so they are safe and will not harm the baby

41
Q

What are the problems with X-ray photographs and CT scans?

A

X-rays are ionising so they can cause cancer if you’re exposed to too high a dose - CT scans use even more X-ray radiation so are even more harmful

42
Q

Why are children more at risk from the effects of radiation than adults?

A

Because children are still growing and so are much more sensitive to cell damage from radiation

43
Q

What produces the best image quality out of ultrasounds, X-ray photographs and CT scans?

A

CT scans, followed by X-ray photographs and then ultrasounds

44
Q

What is the image quality of ultrasounds?

A

They are typically fuzzy, making harder to diagnose some conditions using these images

45
Q

What is the image quality of X-ray photographs?

A

They produce clearer images (than ultrasounds) of bones and metal, but not much else

46
Q

What is the image quality of a CT scan?

A

They produce detailed, high resolution, images and can be used to diagnose complicated illnesses - 3D images can also be made from CT scans

47
Q

What is refraction?

A

When waves change direction as they enter a different medium

48
Q

What is the angle of incidence?

A

The angle the incident (incoming) ray makes with the normal

49
Q

What is the angle of refraction?

A

The angle the refracted ray makes with the normal

50
Q

Why does refraction occur?

A

Due to the change in density from one medium to another - which changes the speed of the waves

51
Q

What happens when light enters a more dense medium?

A

It slows down, and bends towards the normal

52
Q

What happens when light enters a less dense medium?

A

It speeds up, and bends away fro the normal

53
Q

When does light not refract?

A

When a wave hits a boundary 90° it will not change direction

54
Q

When light hits a medium, will all the light pass through the medium?

A

No some will be reflected - it all depends on the angle of incidence

55
Q

What is the refractive index of a medium?

A

The ratio of the speed of light in a vacuum to the speed of light in that medium

56
Q

What types of materials have refractive indexes?

A

Transparent materials

57
Q

What is the formula to find the refractive index of a material?

A

refractive index (n) = sin i / sin r ==> ‘i’ is the angle of incidence, and ‘r’ is the angle of refraction

58
Q

What are the two types of lenses called?

A

Converging (convex) and diverging (concave)

59
Q

What is the shape of a converging lens?

A

It bulges outwards

60
Q

What does a converging lens do to parallel rays of light?

A

It causes them to move together (converge) at the principle focus

61
Q

What is the axis of a lens?

A

A line passing through the middle of the lens (horizontal)

62
Q

Where is the principal focus of a converging lens?

A

Where all the rays hitting the lens parallel to the axis all meet

63
Q

What is the distance from the centre of the lens to the principal focus called?

A

The focal length

64
Q

Where is the principal focus found on a convex lens?

A

On each side of the lens

65
Q

What happens when an incident ray travels parallel to the axis and refracts through the converging lens?

A

The ray passes through the principal focus on the other side

66
Q

What happens when an incident ray travels directly through the centre of a converging lens?

A

It carries on in the same direction after passing through the lens

67
Q

What happens when an incident ray passes through the principal focus before passing through a converging lens?

A

The ray refracts through the lens and travels parallel to the axis

68
Q

What is the shape of a diverging lens?

A

It is concave - it caves inwards

69
Q

What does a concave lens do to parallel rays of light?

A

It causes them to spread out (diverge)

70
Q

What is the principal focus of a diverging lens?

A

The point where rays hitting the lens parallel to the axis appear to all come from

71
Q

How do you find the principal axis of a diverging lens?

A

By tracing the rays back until they all appear to meet

72
Q

What is the focal length of a diverging lens?

A

The same as converging lenses - the distance between the centre of the lens and the principal focus

73
Q

What happens when an incident ray parallel to the axis refracts through a diverging lens?

A

It travels in line with the near-side principal focus (it appears to have come from the principal focus)

74
Q

What happens when an incident ray passes directly through the middle of a diverging lens?

A

It carries on in the same direction

75
Q

What happens when an incident ray is passing through a diverging lens towards the far-side principle focus?

A

It refracts through the lens and travels parallel to the axis

Physics Michael (14 decks)

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