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BDS3: Clinical dental sciences > Dental Radiology > Flashcards

Dental Radiology Flashcards

1
Q

what are x-rays a form of?

A

electromagnetic radiation

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2
Q

what are the properties of electromagnetic radiation?

A

 No mass
 No charge
 Travel speed of light
 Travel in vacuum

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3
Q

what are the 7 main groups on the EM spectrum?

A

 Divided into 7 main groups
* Gamma ray (shortest wavelength, highest frequency, highest energy)
* X - ray
* Ultraviolet
* Visible
* Infrared
* Microwave
* Radio (opposite gamma)

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4
Q

how is frequency described?

A

how many times waves shape repeats per unit time

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5
Q

what are the units of frequency and what does it mean?

A
  • In hertz
  • One hertz = one cycle per second
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6
Q

what is the description of wavelength?

A

distance over which wave shape repeats

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7
Q

what is the formula for speed?

A

Speed = frequency X wavelength

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8
Q

What is the speed of EM?

A

speed of light

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9
Q

what happens if frequency increases?

A

wavelength decreases

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10
Q

how are photons known?

A

o Em radiation involves the movements of energy as packets of energy known as photons

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11
Q

what is photon energy measured in?

A

o Energy usually measured in electron volts, eV

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12
Q

what are photon energies in x-rays? (number)

A

124eV

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13
Q

what are the 2 types of x-rays

A

 Hard (higher energies)
* Able to penetrate human tissues
 Soft (lower energies)
* Easily absorbed

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14
Q

what are properties of x-rays?

A

 Form of EM radiation
* No mass
* no charge
* very fast
* travel in vacuum
 undetectable to human senses
 man made
 cause ionisation

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15
Q

describe the basic production of x-rays?

A

 electron fired at very high speed
 collision – kinetic energy converted to EM radiation and heat
 photons aimed at a subject

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16
Q

what is the central nucleus made up of?

A
  • Protons
    o Number of these = atomic number (Z)
  • Neutrons
  • Mass number (A) = no. protons + neutrons
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17
Q

what is the innermost electron shell?

A

K

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18
Q

what are the max no. electrons a shell can hold

A

o K= 2, L= 8, M=18, N=32

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19
Q

how are orbiting electrons held within their shells?

A

electrostatic force

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20
Q

what is description of binding energy?

A

 Binding energy = additional energy required to exceed electrostatic force and remove an electron from shell

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21
Q

what shell has the highest binding energies?

A

K shell

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22
Q

what does a more positive charged nucleus mean?

A

greater electrostatic force

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23
Q

what is the enrgy requeired to move an electron to a more outer shell?

A

Diff in biding energies of 2 shells, if to a more inner shell energy is released

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24
Q

what is current described as?

A

 Flow of electric charge, usually by movement of electrons

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25
Q

what is unit of current?

A
  • Measure of how much charge flows past a point per sec
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26
Q

what are the descriptions of Direct and alternating current?

A
  • Direct current (DC) = constant unidirectional flow
  • Alternating current (AC) = flow repeatedly reverses direction
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27
Q

what is voltage described as?

A

 Diff in electrical potential between 2 points in an electrical field

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28
Q

what does a transformer do?

A

 Alter the voltage and current from one circuit to another

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29
Q

what are the 2 separate transformers required for an x-ray unit?

A

step up and step down transformer

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30
Q

what does a step up transformer do?

A
  • Increase potential diff across x-ray tube
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31
Q

what is the voltage of a step up transformer?

A

usually 60-70 kV

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32
Q

what is the current reduced to in a step up transformer?

A

milliamps (mA)

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33
Q

what is description of a step down transformer?

A
  • Decrease potential diff across filament
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34
Q

what does x-ray production require?

A

requires a unidirectional current

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35
Q

what doe x-ray units powered by?

A

mains electricity (AC)

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36
Q

what do x-ray unit generators do? and what is process known as?

A

modify AC so it mimics a constant DC
process known as recitfiication

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37
Q

what is intensity proportional to?

A

 Proportional to current in filament (mA) and potential diff across x-ray tube (kV)

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38
Q

what is intensity of beam inversely proportional to?

A

o Intensity of beam inversely proportional to square of distance between x-ray source and the point of measurement
o Therefore doubling distance will quarter dose

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39
Q

explain basics of collision between electrons and atoms?

A

o Electrons accelerated towards atoms at high speed
o Collison. Kinetic energy of these electrons -> EM radiation (ideally x-ray photons) + heat
o X-ray photons aimed at subjected

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40
Q

what are x-ray tube components?

A
  • glass envelope
  • cathode (-ve)
  • anode (+ve)
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41
Q

what is purpose of glass envelope?

A

o Vacuum inside
o Air tight enclosure

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42
Q

in cathode what is passed through wire?

A

 Low-voltage, high current electricity passed through wire

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43
Q

how are electrons released from atoms in wire for cathode?

A

thermionic emission

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44
Q

greater current in filament in cathode means what?

A

 Greater current in filament -> greater heat + greater no. electrons

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45
Q

what is cathode filament made of?

A

tungsten

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46
Q

what are properties of filament in cathode?

A
  • High melting point
    o Can withstand high temps
  • High atomic number (Z=74)
  • Malleable
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47
Q

what does focusing cup in cathode do?

A
  • (-) charged -> repels electrons released at filaments
  • Shaped to focus on small point on anode target
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48
Q

what is focusing cup in cathode made of?

A

molybendum

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49
Q

what does target in anode produce?

A

photons

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50
Q

what is target in anode made of?

A

tungsten

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51
Q

what is focal spot on target?

A

 Focal spot = precise are on target where electrons collide and x-rays are produced (i.e x-ray source)

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52
Q

what is a problem with focal spot angulation? and how does focal spot size matter with this?

A

heat
 Less 1 percent of kinetic energy from electrons is converted to x-ray photons. (almost all into heat)
 Smaller focal spot size = greater image quality but great heat concentration

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53
Q

what is solution to problem for focal spot in target?

A

angled target?

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54
Q

how does an angled target help in producing x-rays?

A

 Increase actual surface area where electrons impact = better heat tolerance
 Reduces the apparent SA from where beam is emitted = smaller penumbra effect

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55
Q

what is heat dissipating block made of?

A

copper

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56
Q

what is cathode anode relationship?

A

o High voltage electricity passed through x-ray tube
- High potential diff between (-) cathode and
(+) anode
o Electrons released at filament are repelled away from cathode and attracted to anode
- Accelerate to very high speed over very short
distance
* Up to half speed of light
-Greater potential diff -> greater acceleration ->
greater kinetic energy

Electrons have high kinetic energy when colliding with anode target

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57
Q

what does step down transformer decrease potential difference to?

A

10V

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58
Q

what is electron volts (eV) used to measure?

A

o Units used to measure kinetic energy gained by electrons as they accelerate from cathode to anode

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59
Q

what is penumbra effect?

A

o Blurring radiographic image due to focal spot not being a single point (but rather a small area)
 Minimised by shrinking size of focal spot

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60
Q

what does collimator do?

A

reduces pt dose

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61
Q

why should you use rectangle collimators?

A

o Can reduce SA irradiated by almost 50 percent

62
Q

what does aluminium filtration in tubehead do? and what are the thicknesses required?

A

 Removes lower energy (non-diagnostic) x-rays from beam
 Min thickness aluminium required
* <70kV -> 1.5mm
* >= 70kV -> 2.5mm

63
Q

what does spacer cone dictate?

A

 Dictate distance between focal spot and pt

64
Q

what are specific sizes required for focus to skin distance?

A

 <60 kV -> 100mm
 >= 60 kV -> 200mm

65
Q

what does altering focus skin distance do?

A
  • Altering fsd will affect degree of divergence of x-ray photons in beam
    o Increasing fsd reducs divergence of beam so therefore reduces magnification of image
66
Q

what are the diff types of interactions that produce x-rays?

A

continuous radiation interactions
characteristic radiation interactions

67
Q

what is description of continuous radiation interactions?

A

 Bombarding electron passes close to target nucleus, causing to be decelerated and deflected -> lost kinetic energy released as x-ray photons

68
Q

how is max energy achieved in continous radiation interactions?

A
  • Max energy achieved when electron collides directly with nucleus and stops completely
69
Q

what is description of characteristic radiation interactions?

A

bombarding electron collides with an inner shell electron and either
* Displaces it into a more peripheral shell – excitation
* Removes it completely – ionisation

70
Q

what happens when an electron ‘drops’ to a lower shell?

A
  • When an electron ‘drops’ to a lower shell it loses energy which is emitted as a photon of specific energy
71
Q

what are the comparison between continous and characteristic interactions?

A

 Continuous
* Produces continuous range of x-ray photon energies
* Max photon energy matches peak voltage
* Bombarding electron interacts with nucleus target atom
 Characteristic
* Produces specific energies of x-ray photon, characteristic to element used for target
* Photon Energies depend on binding energies of electron shells
* Bombarding electron interacts with inner shell electrons of target atom

72
Q

how can photons in a diagnsotic x-ray beam interact with matter?

A

 transmission – passes through matter unaltered
 absorption – stopped by matter
 scatter – changes direction

73
Q

what does attenuation mean?

A

reduction in intensity of beam

74
Q

what does scattered plus absorbed mean?

A

attenuation

75
Q

what are number of photons in x-ray beam affected by?

A

current in filament (mA)
greater mA –> geater no. photons

76
Q

hwo does attenuation indirectly lead to radiographic image?

A

o diff tissues/materials have varying degrees of attenuation which determines how many photons reach the receptor
o minimal attenuation -> black
o partial attenuation -> grey
o complete attenuation -> white

77
Q

what is photoelectric effect?

A

complete absorption
- * photon in beam interacts with inner shell electron -> results in absorption of photon -> creation of photoelectron

78
Q

what does absorption by photoelectric effect lead to?

A

 absorption by photoelectric effect prevents x-ray photons reaching receptor -> leads to lighter area on image

79
Q

what is compton effect?

A

partial absorption and scatter
- * Photon in beam interacts with outer shell electron -> results in partial absorption and scattering of photon -> creation of recoil electron

80
Q

in compton effect incoming photon is what?

A

much greater than binding energy

81
Q

what is electron ejected in compton effect called?

A

recoil electron

82
Q

how is direction of scatter in compton effect dictated?

A

o Higher energy photons are defected more forward -> ‘forward scatter’
o Lower energy photons are deflected more backward -> ‘back scatter’
- majority of scatter from beam is forward

83
Q

what does scatter in compton effect lead to?

A

o Causes darkening of image in wrong place
o Results in ‘fogging’ of image -> reduces image contrast/quality

84
Q

how is scatter reduced?

A

collimation

85
Q

what is effect of radiation dose from the 2 effects?

A

 Increase pt dose but is necessary for image formation
 Increase pt dose but scattered photons do not contribute usefully to image

86
Q

what is the effect of lowering kV on x-ray unit?

A

o Lower x-ray tube pd (kV) leads to ->
o Overall lower energy photons produced leads to ->
o Increase photoelectric effect interactions leads to ->
o Increase contrast between tissue with diff Z BUT
o Increase in dose absorbed by pt

87
Q

effect of raising kV on x-ray unit?

A

o Higher x-ray tube pd (kV) leads to ->
o Overall higher enrgy photons produced leads to ->
o Decrease photoelectric effect interactions (+ increase in forward scatter) leads to ->
o Decrease dose absorbed by pt BUT
o Decrease in contrast between tissues with diff Z

88
Q

what is the comparison between 2 interactiosn adn 2 effects

A

interactions
- occur x-ray tube
- electrons interact with tungsten atoms
- lead to production of x-ray photons

effects
- occur in pt/receptor/shielding
- x-ray photons interacting with atoms
- lead to attenuation of beam

89
Q

what is the approx energy each ionisation process will deposit?

A

35eV

90
Q

what causes damage in indirect dna damage?

A

free radicals

91
Q

what are factors of biological effect of dna damage?

A

 Type radiation
 Dose
 Dose rate
* Low rate – cells can repair damage before further damage occurs
* High - dna repair capacity likely overwhelmed
 Tissue or cell type irradiated

92
Q

what does tissue radiosensitivty depend on

A
  • Function of cells that make up tissues
  • If cells are actively dividing
93
Q

what are possible outcomes after radiation hits a cell nucleus?

A
  • DNA mutation
    o Mutation repaired
     Viable cell
    o Cell death
     Unviable cell
    o Cells survives but is mutated
     Cancer
  • no change
94
Q

what is units of absorbed dose?

A

gray

95
Q

how is equivalent dose calculated and what is its units?

A
  • Absorbed dose multiplied by a weighting factor depending on type of radiation
  • For beta, gamma and x-rays the weighting factor is 1. For alpha particles it is 20
  • Units – sieverts (Sv)
96
Q

what are the 2 types of radiation effects?

A

deterministic effects
stochastic effects

97
Q

describe deterministic effects?

A
  • Tissue reactions
  • Only occur above a certain (threshold) dose
  • Severity of effect is related to dose received
  • Unusual to see in radiology although possible in high dose areas such as interventional radiology
  • Effects will show a few days after exposure
98
Q

describe stochastic effects?

A
  • Probability of occurrence is related to dose received
  • No known threshold for stochastic effects
    o There is no dose below which effects will not occur
  • Cannot predict if these effects will occur in an exposed individual or how severe
    o Likelihood of effect increases as dose increases
  • Effects can develop years after exposure
99
Q

stochastic effects are subdivided into 2 categroies?

A

o Somatic – results in disease or disorder
o Genetics – abnormalities in descendants

100
Q

what is effective dose from an intra oral x-ray

A

0.005mSv

101
Q

how far away is controlled area?

A

1.5m from x-ray tube

102
Q

describe radiation protection philosphophy?

A

o Justification
 Must have sufficient benefit to individuals or society in order to offset detriment
o Optimisation
 Doses and no. people exposed should be as low as reasonably practicable (ALARP), taking into account economic and social factors
o Dose limitation
 System of individual dose limits so that the risks to individuals are acceptable

103
Q

describe dose optimisation?

A

 Dose ALARP
* Still maintain image quality
* Circular collimated have been shown to increase dose by 40 percent
o Must use rectangular collimators
 Pt doses can be reduced in a variety of methods
* Use E speed film or faster
* Use a kV range 60-70
* Focus to skin distance should be >200mm
* Use rectangular collimation

104
Q

what are diagnostic reference levels?

A

o Legislation requires employers to have established dose levels for typical exams for standard sized patients
o Comparative standard used in optimisation
o Compared to national ref levels
o Individual x-ray units are compared to DRLs and national ref levels
 Enables identification of units giving higher doses

105
Q

what are current DRL’s for intra oral exams?

A

 Adult:
* 0.9 mGy – digital sensors
* 1.2 mGy – phosphor plates and film
 Child
* 0.6 mGy – digital sensors
* 0.7 mGy – phosphor plates and film

106
Q

what are diff types of digital x-ray receptors?

A

phosphor plate
solid state sensor

107
Q

how are phosphor plate images created?

A

o Within patients mouth
 1 receptor exposed to x-ray beam
 2 phosphor crystals in receptor excited by x-ray energy, resulting in creation of a latent image
o Within scanner
 3 receptor scanned by a laser
 4 laser energy causes excited phosphor crystals to emit visible light
 Light is detached and creates digital image

108
Q

what are 2 types of solid state sensors

A

charge couple device
complimentary metal oxide semi conductor

109
Q

what are phosphor plate sizes?

A

 E.g size 0 (anterior periapicals)
 Size 2 (bitewings, posterior periapicals)
 Size 4 (occlusal radiographs)

110
Q

describe conversion of x-ray shadow into image?

A

o When Beam passes through an object some photons are attenuated creating an ‘x-ray shadow’
o X-ray shadow is basically the image ‘formation’ held by the x-ray photons after an x-ray beam has passed through an object
o Image receptor detects this shadow and uses it to create an image

111
Q

what is the format for Digital image?

A

Digital imagine and communications in medicine

112
Q

what is management of digital images?

A

picture archiving and communication system

113
Q

how to view digital radiographs?

A

o Environment
 Subdued lighting
 Avoid glare
o Monitor
 Clean
 Adequate resolution
 High enough brightness
 Suitable contrast

114
Q

explain diffs between phosphor plates and solid state sensors?

A

o Phosphor plates
 Thinner, lighter and flexible
 Wireless -> more stable (more comfortable)
 Variable room light sensitivity -> risk of impaired image
 Latent image needs to be processed in scanner separately
 Handling similar to film
o Solid-state sensors
 Bulkier and rigid
 Usually wired
 Smaller active area (for same physical area of receptor)
 No issues with room light control
 Arguably more durable -> replaced less often
 More expensive

115
Q

how is film speed affected?

A

 Greater speed -> smaller radiation required to achieve an image
 Affected by no. and size of silver halide crystals
* Larger crystals -> faster film but poorer image quality

116
Q

what are diff methods of film processing?

A
  • Manual
  • Automated
  • (self-developing films)
117
Q

steps to film processing?

A
  • 1 developing
    o Converts sensitised crystals to black metallic silver particles
  • 2 washing
    o Removes residual developer solution
  • 3 fixing
    o Removes non sensitised crystals
    o Hardens emulsion (which contains the black metallic silver)
  • 4 washing
    o Removes residual fixer solution
  • 5 drying
    o Removes water so that film is ready to be handled/stored
118
Q

describe manual (or wet) cycle?

A

 Person dips film into diff tanks of chemicals
* At precise conc/temps
* For specific periods of time
* Washes film after each tank
 Must be carried out in dark room with absolute light tightness and adequate ventilation

119
Q

describe the processing issue of fixing?

A

 Involves reaction to remove non-sensitised crystals and hardens remaining emulsion
 Inadequate fixing means non-sens crystals left behind
* Image green-yellow or milky
* Image becomes brown over time

120
Q

describe processing issue of washing?

A

 Developing and fixer solution will continue to act if not washed off

121
Q

digital vs film?

A

o Digital
 Advantages
* No need for chemical processing
* Easily storage and archiving images
* Easy back up images
* Images can be integrated into pt records
* Easy transfer images
* Images can be manipulated
 Disadvantages
* Worse resolution -> risk pixelation
* Requires diag-level computer for opimal viewing
* Risk of data corruption
* Hard quality prints have poor image quality
* Image enhancement can create images misleading

122
Q

common types of extra oral radiographs?

A

o Panoramic
o Cephalometric radiographs
 Lateral
 Postero-anterior
o Oblique lateral radiographs
o Skull radiographs
 Occipitomental
 Postero-anterior skull/mandible
 Reverse towne’s
 True lateral

123
Q

describe angulation of beam?

A
  • True = perpendicular to head
  • Oblique = not perpendicular to head
124
Q

what are examples of reference lines/planes?

A

 Mid sagittal plane - line down middle face
 Interpupillary line – connects both pupils
 Frankfort plane – connects infraorbital margin and superior border of external auditory meatus
 Orbitomeatal line – connects outer canthus and centre of EAM
* A.k.a canthomeatal line or radiographic baseline

125
Q

what is cephalometry?

A

o Measurement and study of the head

126
Q

what is lateral cephalogram used for in ortho?

A

 Assess skeletal discrepancy when appliance used for labio lingual movement of incisors
 Aids location and assessment of unerupted, malformed and misplaced teeth
 Indicates upper incisor root length

127
Q

what are oblique lateral radiographs used to assess?

A
  • Dental pathology
  • Unerupted teeth
  • Mandibular fractures
  • Lesions
128
Q

describe need for radiographic localisation>

A

o to determine location of structure or pathological lesion in relation to other structure

129
Q

what are the options for views at right angles in relation to radiography localisation?

A

o OPT and lower true occlusal
o Paralleling periapical and lower true occlusal
o CBCT

130
Q

describe methods of radiographic localisation?

A

o Normally 2 views required
o Views at right angles in their projection geometry
o Views with any diff projection, provided the diff is known
o With aid of opaque objects (e.g gutta percha point)
o Anatomical knowledge crucial

131
Q

describe parallax and how it work?

A

o An apparent change in position of an object, caused by a real change in the position of the observer
o How it works:
 Imagine looking in a cupboard and objects appear to change their relationship to each other and you

132
Q

what are prallax localisation options?

A

o Horizontal tube shift – equivalent views
 2 periapicals
 2 bitewings
 2 oblique occlusals
o Vertical tube shift – diff views
 OPT and oblique occlusal
 OPT and lower (bisecting angle) periapical

133
Q

describe parallax localisation?

A

o 1. Take 2 radiographs of same object
o 2. Identify direction tube movement
o 3. Arrange on viewing box
o 4. ? is this correct

134
Q

who do you need input from with regards to the quality assurance program?

A

o input from medical physics expert (role defined in IRMER17)

135
Q

what are things to check for a digital image receptor?

A

 1. Receptor itself
* Visible damage to casing/wiring
* Check if clean
 2. Image uniformity
* Expose receptor to unattenuated beam and check if image is uniform
 3. Image quality
* Take radiograph of test object and assess against baseline

136
Q

how to tell if phosphor plates are damaged?

A

 Scratches -> white lines
 Cracking from flexing -> network white lines
 Delamination -> white area around edge
* i.e separation of phosphor layer from base plate

137
Q

how to tell if solid state sensors are damaged?

A

 sensor damage -> white squares

138
Q

how to tell if film images are damaged?

A

 damage often appears as black marks due to sensitisation of radiographic emulsion
 may appear white if emulsion is scraped off

139
Q

how to test image quality?

A

o Step wedge
 Type test object used to check quality/contrast
 Exposed to normal clinical exposure and compared to baseline
* Baseline – must be able to differentiate all 6 steps
* Carried out regularly

140
Q

what are the 3 p[arts of assessing clinical image quality?

A

 1. Image quality rating
* Grading each image
 2. Image quality analysis
* Reviewing images to calculate ‘success rate’ and identify any trends for suboptimal images
* Carried out periodically
 3. Reject analysis
* Recording and analysis each unacceptable image

141
Q

what is the recommended QA system and what are the quality ratings?

A

o FGDP
 Quality rating
* Diag acceptable (‘A’)
* Diag not acceptable (‘N’)

142
Q

what is diag acceptable position factor of bitewings?

A

 Show entire crowns of upper and lower teeth
 Include distal aspect of canine and mesial aspect of last standing tooth
* May require more than 1 radiograph
 Every approximal surface shown at least once without overlap (where possible)
* May be impossible if crowding

143
Q

what is diag acceptable position of periapicals?

A

 Shows entire root
 Shows periapical bone
 Shows crown

144
Q

what most all radiographic images be in order to be diag acceptable?

A

o Must have adequate contract, sharpness, and resolution as well as minimal distortion

145
Q

what are some potential causes to a too dark or pale image?

A

o Exposure factors
 Incorrect setting, pt tissues too thick, fault x-ray timer
o Developing factors (film)
 Incorrect duration, incorrect temp, incorrect conc
o Viewing factors
 Inappropriate light source (film), inappropriate display screen (digital), excessive environmental light

146
Q

what are some potential faults of an image?

A
  • too dark or pale
  • poor contrast
  • unsharp
  • distorted
  • over-collimated
  • receptor marks
147
Q

what makes better heat tolerance?

A

Increase SA of place electron interact

148
Q

What makes a smaller penumbra effect?

A

Reduction in apparent SA where beam is emitted

149
Q

What is excitation of an electron?

A

When it moves to a more peripheral shell

150
Q

What is effective dose and how is it calculated?

A
  • it is calculated using equivalent dose times tissue weighting factor
151
Q

what is delamination?

A

White area around edge

152
Q

what collimation is used for lateral cephalogram and what does it do?

A

triangular collimation
reduce exposure of cranium

BDS3: Clinical dental sciences (11 decks)

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