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PHYSICS 160 > Section 5: Medical Physics > Flashcards

Section 5: Medical Physics Flashcards

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1
Q

Positive vs negative torque

A

Positive: aims to produce a counterclockwise rotation
Negative: aims to produce a clockwise rotation

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2
Q

Turning effect of a force on a lever depends on…

A

Magnitude of F applied
Position relative to axis of rotation at which F is applied
Angle at which F is being applied relative to lever

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3
Q

Conditions for equilibrium

A

Net external F on system is zero

There is a balance in torque or rotational effect of forces

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4
Q

Rigid body - conditions for equilibrium

A

Zero translational acceleration

Zero angular acceleration

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5
Q

Centre of gravity - adult vs young child

A

Adult: around hips - lower COM –> good stability

Young child: near shoulders - high COM –> poor stability

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6
Q

Increasing stability

A

Standing with legs apart - increases size of base and lowers centre of gravity
Walking frames - increase size of base

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7
Q

Deformation

A

A change in shape caused by applied forces

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8
Q

Elasticity

A

Ability of materials to deform under load in a recoverable way

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9
Q

Plasticity

A

Permanent deformations caused by applied loads

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10
Q

Stress

A

Force per unit area

Like pressure, but can be diff in diff directions

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11
Q

Strain

A

A measure of the change in shape
Dimensionless
Compressive strain = -ve

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12
Q

Types of stress

A

Tensile stress = +ve

Compressive stress = -ve

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13
Q

Pressure vs stress - state

A

Pressure often used with fluids, gases

Stress often used with solids

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14
Q

Pressure vs stress - direction

A

Pressure acts perpendicular to surface

Stress can be perpendicular or parallel to surface

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15
Q

Shear stress

A

Stress parallel to a surface

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16
Q

Young’s modulus

A

E
AKA modulus of elasticity
Bigger E = stiff
Smaller E = compliant

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17
Q

Constitutive law

A

The stress-strain relationship for soft tissues

Non-linear

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18
Q

Tendons are composed of…

A

Collagen and elastin, which combine to give an apparent increase in stiffness with increasing strain

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19
Q

Collagen

A

For small strains, doesn’t contribute resistance as strings straighten
At larger strains, collagen is straight and resists extension –> increases apparent stiffness

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20
Q

Sound

A

A longitudinal pressure wave

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21
Q

Purpose of ear

A

To convert small changes in pressure of sound (compressions and rarefactions) into electrical signals that are interpreted by the brain

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22
Q

A single-frequency periodic waveform can be described by its…

A

Frequency
Amplitude
Phase

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23
Q

High-frequency vs low-frequency sound

A

High f: High no of cycles per second –> high-pitched

Low f: Low no of cycles per second –> low-pitched

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24
Q

High vs low intensity sound

A

High intensity: Large A

Low intensity: Low A

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25
Q

Fourier’s theorem

A

States that any complex signal can be synthesised by the addition of single-frequency waves of various amplitudes and phases
Similarly, any complex periodic waveform can be decomposed into its frequency components

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26
Q

Sawtooth wave

A

Many frequency components added tgt

Gives rise to a sharp wave

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27
Q

Human ear - main components

A

Outer, middle, inner ear

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28
Q

Outer ear - purpose

A

Collects sound and directs it into ear canal

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29
Q

Middle ear - purpose

A

Transfers sound from eardrum (tympanic membrane) into oval window via a lever system

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30
Q

Inner ear - purpose

A

Sorts sound into its frequency components and sends info to brain for processing

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31
Q

Outer ear - pinna

A

Outermost part of ear

Collects sound and directs them into ear canal

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32
Q

Middle ear - ossicles

A

3 tiny bones that are elastically collected tgt:
Hammer (malleus)
Anvil (incus)
Stirrup (stapes)

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33
Q

Middle ear - sound is _____

A

Amplified

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34
Q

Inner ear - cochlea

A

Snail-shaped structure

Contains tiny hair cells that convert vibration into electrical potentials

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35
Q

Inner ear - high vs low frequencies

A

High: cross over near windows
Low: cross over at far end

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36
Q

Intensity level - logarithmic scale

A

Small changes in intensity level can have significant consequences in noise dose

37
Q

Loudness

A

The perception of intensity

38
Q

What is loudness of a sound dependent on

A

Frequency of sound

39
Q

Loudness - unit

A

Phon

40
Q

Fletcher-Munson curves

A

Shows lines of equal loudness in phones

41
Q

Threshold of hearing

A

The min intensity the human ear can detect at a given frequency
0 phones

42
Q

Threshold of pain

A

120 phon

43
Q

Sound below 0 phon line

A

Any sound represented by a point below the 0 phon line won’t be heard by a ‘normal’ ear

44
Q

Hearing loss is often ______ specific

A

Frequency

45
Q

What can hearing loss be caused by

A 
Excessive exposure to noise
Illness
An accident
An inherited disorder
Age
46
Q

Presbycusis

A

Progressive hearing loss due to age - particularly in high-frequency range

47
Q

Types of hearing loss

A

Conductive HL

Sensorineural HL

48
Q

3 dB exchange rate

A

For every increase in 3 dB of intensity level, the max allowable duration of exposure is halved

49
Q

Factor daily dose (FDD)

A

The amount of noise dose a person receives relative to the max allowable level

50
Q

Audiometer

A

Tests a person’s hearing

Generates sound signals of various frequencies at diff intensities so the threshold of hearing can be detected

51
Q

Conductive hearing loss

A

When the passage of sound is blocked either in the ear canal or in the middle ear

52
Q

Sensorineural hearing loss

A

Due to a disorder in the cochlea or in the auditory nerve

53
Q

Ideal flow - conditions

A

Incompressible fluids
Non-viscous flow
Steady flow
Streamline flow

54
Q

Viscosity

A

Internal resistance of liquid

55
Q

Viscosity - real fluid

A

Liquid at surface of pipe is stationary and v is max at centre
Velocity profile is parabolic
Referred to as Poiseuille flow

56
Q

Coefficient of viscosity (η)

A

Very runny fluid = low viscosity

Sticky fluid = high viscosity

57
Q

Poiseuille’s law

A

Takes into account viscosity

Only valid if flow remains laminar

58
Q

Reynolds number (Re)

A

Dimensionless

Gives indication of likely state of flow (laminar or turbulent)

59
Q

Pathway of light to eye

A 
Cornea
Aqueous humour
Lens
Vitreous humour
Retina
60
Q

Where does most bending of light / refraction occur in the eye

A

Cornea

Due to curved surface and big difference of index of refraction

61
Q

Where are images formed in the eye

A

Retina

62
Q

Retina

A

Consists of photoreceptors which convert images into neural signals –> sent to brain via optic nerve

63
Q

Optical power (P) - units

A

Diopters (D)

64
Q

Eye: Lens

A

Focal length of lens (and thus power of lens) must be able to change / accommodate for objects to be seen clearly at a range of distances

65
Q

Normal vision

A

Near point = 25cm
Far point = infinity
Range of vision = 25cm to infinity

66
Q

Near point

A

The distance to the closest point a person can see clearly

67
Q

Far point

A

The distance to the most distant point a person can see clearly

68
Q

Range of vision

A

Near point to far point

69
Q

Lens of curvature - close vs near objects

A

For close objects: lens must increase in curvature
For distant objects: lens must flatten

Normal eye relaxes when viewing distant objects

70
Q

Near-sightedness (myopia) - caused by?

A

Lens being too strong or eye being too long

71
Q

Near-sightedness (myopia) - corrected by?

A

Diverging corrective lens - reduces effective power of a lens that is too powerful to achieve clear vision
Creates a close image at far point of eye –> clearly visible

72
Q

Far-sightedness (hyperopia) - caused by

A

Lens being too weak (flat)
Eye being too short
From a deterioration in ability of eye to accommodate- often due to age

73
Q

Far-sightedness (hyperopia) - corrected by

A

Converging corrective lens - supplies additional power to eye system
Creates a distant image at near point of eye –> clearly visible

74
Q

Glasses and contact lenses - assumptions

A

Assume glasses sit 2cm from front of eye

Assume contact lenses sit directly on eye

75
Q

Medical imaging - non-invasive

A

Allows medical professionals to visualise internal anatomy without the need for invasive surgery

76
Q

How are X-rays produced

A

Using an x-ray tube
Heated filament produces e- which goes to the metal target, which produces X-rays
All of this is contained with a vacuum / evacuated chamber

77
Q

Energy of x-ray photons is usually quoted in…

A

eV

78
Q

2 processes that x-rays are produced

A

Characteristic x-rays

Bremsstrahlung

79
Q

X-rays: Characteristic x-rays

A

If e- are travelling with sufficient E, they can knock e- out of inner shells of atoms in the target –> vacancy is filled by an e- from outer shells of atom
As the e- moves to a lower-energy shell, they emit the excess energy as x-rays

80
Q

X-rays: Bremsstrahlung

A

Incident e- slow down when they hit the target and lose some KE as they’re decelerated
Radiation resulting from deceleration is known as bremsstrahlung
Distribution of these energies is continuous

81
Q

X-ray spectrum

A

The distribution of the x-ray intensity per unit wavelength vs photon wavelength

82
Q

X-rays: Attenuation

A

The process that causes the no of photons to decrease as an x-ray beam passes through the body

83
Q

X-rays: What does the degree of attenuation depend on

A

Composition of tissue - more dense and higher atomic no = higher amount of attenuation = bright, e.g. bone

84
Q

X-rays: Dark vs bright

A

If more x-rays pass through patient and hit detector = dark

85
Q

X-rays: What is the image that is produced called

A

Projection image

86
Q

X-rays: Trade-off

A

Increased image size = decreased sharpness

87
Q

X-rays: SID vs SOD

A 
SID = source-to-image distance
SOD = source-to-object distance
88
Q

X-rays: Where is the image projected

A

X-ray detector

89
Q

Computed tomography (CT)

A

X-ray tube and detector rotate around the patient at high speeds to quickly obtain many projection images

PHYSICS 160 (5 decks)

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