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PHYSICS 160 > Section 5: Medical Physics > Flashcards

Section 5: Medical Physics Flashcards

(89 cards)

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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
Fourier's theorem
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
26
Sawtooth wave
Many frequency components added tgt | Gives rise to a sharp wave
27
Human ear - main components
Outer, middle, inner ear
28
Outer ear - purpose
Collects sound and directs it into ear canal
29
Middle ear - purpose
Transfers sound from eardrum (tympanic membrane) into oval window via a lever system
30
Inner ear - purpose
Sorts sound into its frequency components and sends info to brain for processing
31
Outer ear - pinna
Outermost part of ear | Collects sound and directs them into ear canal
32
Middle ear - ossicles
3 tiny bones that are elastically collected tgt: Hammer (malleus) Anvil (incus) Stirrup (stapes)
33
Middle ear - sound is _____
Amplified
34
Inner ear - cochlea
Snail-shaped structure | Contains tiny hair cells that convert vibration into electrical potentials
35
Inner ear - high vs low frequencies
High: cross over near windows Low: cross over at far end
36
Intensity level - logarithmic scale
Small changes in intensity level can have significant consequences in noise dose
37
Loudness
The perception of intensity
38
What is loudness of a sound dependent on
Frequency of sound
39
Loudness - unit
Phon
40
Fletcher-Munson curves
Shows lines of equal loudness in phones
41
Threshold of hearing
The min intensity the human ear can detect at a given frequency 0 phones
42
Threshold of pain
120 phon
43
Sound below 0 phon line
Any sound represented by a point below the 0 phon line won't be heard by a 'normal' ear
44
Hearing loss is often ______ specific
Frequency
45
What can hearing loss be caused by
``` Excessive exposure to noise Illness An accident An inherited disorder Age ```
46
Presbycusis
Progressive hearing loss due to age - particularly in high-frequency range
47
Types of hearing loss
Conductive HL | Sensorineural HL
48
3 dB exchange rate
For every increase in 3 dB of intensity level, the max allowable duration of exposure is halved
49
Factor daily dose (FDD)
The amount of noise dose a person receives relative to the max allowable level
50
Audiometer
Tests a person's hearing | Generates sound signals of various frequencies at diff intensities so the threshold of hearing can be detected
51
Conductive hearing loss
When the passage of sound is blocked either in the ear canal or in the middle ear
52
Sensorineural hearing loss
Due to a disorder in the cochlea or in the auditory nerve
53
Ideal flow - conditions
Incompressible fluids Non-viscous flow Steady flow Streamline flow
54
Viscosity
Internal resistance of liquid
55
Viscosity - real fluid
Liquid at surface of pipe is stationary and v is max at centre Velocity profile is parabolic Referred to as Poiseuille flow
56
Coefficient of viscosity (η)
Very runny fluid = low viscosity | Sticky fluid = high viscosity
57
Poiseuille's law
Takes into account viscosity | Only valid if flow remains laminar
58
Reynolds number (Re)
Dimensionless | Gives indication of likely state of flow (laminar or turbulent)
59
Pathway of light to eye
``` Cornea Aqueous humour Lens Vitreous humour Retina ```
60
Where does most bending of light / refraction occur in the eye
Cornea | Due to curved surface and big difference of index of refraction
61
Where are images formed in the eye
Retina
62
Retina
Consists of photoreceptors which convert images into neural signals --> sent to brain via optic nerve
63
Optical power (P) - units
Diopters (D)
64
Eye: Lens
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
Normal vision
Near point = 25cm Far point = infinity Range of vision = 25cm to infinity
66
Near point
The distance to the closest point a person can see clearly
67
Far point
The distance to the most distant point a person can see clearly
68
Range of vision
Near point to far point
69
Lens of curvature - close vs near objects
For close objects: lens must increase in curvature For distant objects: lens must flatten Normal eye relaxes when viewing distant objects
70
Near-sightedness (myopia) - caused by?
Lens being too strong or eye being too long
71
Near-sightedness (myopia) - corrected by?
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
Far-sightedness (hyperopia) - caused by
Lens being too weak (flat) Eye being too short From a deterioration in ability of eye to accommodate- often due to age
73
Far-sightedness (hyperopia) - corrected by
Converging corrective lens - supplies additional power to eye system Creates a distant image at near point of eye --> clearly visible
74
Glasses and contact lenses - assumptions
Assume glasses sit 2cm from front of eye | Assume contact lenses sit directly on eye
75
Medical imaging - non-invasive
Allows medical professionals to visualise internal anatomy without the need for invasive surgery
76
How are X-rays produced
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
Energy of x-ray photons is usually quoted in...
eV
78
2 processes that x-rays are produced
Characteristic x-rays | Bremsstrahlung
79
X-rays: Characteristic x-rays
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
X-rays: Bremsstrahlung
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
X-ray spectrum
The distribution of the x-ray intensity per unit wavelength vs photon wavelength
82
X-rays: Attenuation
The process that causes the no of photons to decrease as an x-ray beam passes through the body
83
X-rays: What does the degree of attenuation depend on
Composition of tissue - more dense and higher atomic no = higher amount of attenuation = bright, e.g. bone
84
X-rays: Dark vs bright
If more x-rays pass through patient and hit detector = dark
85
X-rays: What is the image that is produced called
Projection image
86
X-rays: Trade-off
Increased image size = decreased sharpness
87
X-rays: SID vs SOD
``` SID = source-to-image distance SOD = source-to-object distance ```
88
X-rays: Where is the image projected
X-ray detector
89
Computed tomography (CT)
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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