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BDS3 CDS > radiology > Flashcards

radiology Flashcards

1
Q

what is an alpha particle composed of?

A

2 protons and 2 neutrons

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2
Q

how far can an alpha particle travel?

A

few inches

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3
Q

what is a beta particle composed of?

A

electron

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4
Q

how far can a beta particle travel ?

A

few feet

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5
Q

what is the difference between atoms and ions?

A

atoms have equal numbers of protons and electrons, ions do not

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6
Q

when radiation passes through matter, it ionises atoms and deposits energy locally, what is the approximate quantity of energy?

A

35eV

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7
Q

what is the most significant effect of ionising radiation ?

A

DNA damage - can be seen on faulty repair of chromosome breaks

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8
Q

radiation can damage DNA directly and indirectly - describe the direct effect

A

radiation interacts with atoms of a DNA molecule or other important cell components

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9
Q

radiation can damage DNA directly and indirectly - describe the indirect effect

A

radiation interacts with water in the cell producing free radicals which can cause damage

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10
Q

what are free radicals?

A

highly unstable high reactive molecules

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11
Q

which radiation usually is the cause of double strand breaks in DNA?

A

alpha

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12
Q

the biological effect of radiation will depend on a number of factors, list 4

A

type of radiation
amount
time over which dose is received
tissue or cell type irradiated

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13
Q

what is the effect of radiation dose on cell repair capacity?

A

low dose rate - less damaging and cells can repair
high dose rate - DNA repair capacity likely to be overwhelmed

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14
Q

which tissues are at higher risk of cancer following large radiation exposures?

A

oesophagus
thyroid
breast

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15
Q

tissue radio sensitivity is dependent on two factors which are

A

the function of the cells making up the tissue
if the cells are actively dividing

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16
Q

which type of cell are very radiosensitive?

A

stem cells - divide frequently

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17
Q

which cells are less sensitive to radiation?

A

differentiated as the do not divide

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18
Q

true or false
the more rapidly a cell is dividing, the more radiosensitive

A

true

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19
Q

give an example of highly radiosensitive tissue

A

bone marrow
lymphoid tissue
GI

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20
Q

give an example of moderately radiosensitive tissues

A

skin
lung
lens

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21
Q

which tissues are least radiosensitive

A

bone and cartilage
connective tissue
CNS

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22
Q

what are the 4 possible outcomes of radiation hitting the cell nucleus?

A

no change
dna mutation - repaired
dna mutation - cell death
dna mutation - cell survives but is mutated

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23
Q

what is the units of absorbed dose?

A

Gray Gy

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24
Q

what does absorbed dose measure?

A

the energy deposited by radiation

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25
Q

what is the equivalent dose?

A

absorbed dose multiplied by a weighting factor depending on the type of radiation

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26
Q

what are the units for equivalent dose

A

sieverts Sv

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27
Q

what is the weighting factor for alpha particles?

A

20

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28
Q

what is the weighting factor for beta gamma and x-rays

A

1

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29
Q

what is the LNT model (Linear no threshold model) used for ?

A

to estimate the long term biological damage from radiation

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30
Q

what are the assumptions of the LNT model?

A

damage is directly proportional to radiation dose
radiation is always harmful with no safety threshold - several small exposures have same effect as one large

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31
Q

what is the risk of cancer from an intra-oral x-ray?

A

less than 1 in 10,000,000

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32
Q

what is the associated risk of cancer of a dose of 1mSv?

A

1 in 20,000

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33
Q

how can you reduce damage to CR plates?

A

insert between two plastic sheets
clean and replace damaged detectors

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34
Q

what are the adult diagnostic reference levels DRLs for intra-oral examinations?

A

0.9mGy for digital sensore
1.2mGy for phosphor plates and film

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35
Q

what are the current DLRs for child intra oral examinations?

A

0.6mGy digital sensors and 0.7mGy phosphor plates and film

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36
Q

what are the elements of radiation protection philosophy?

A

justification
optimisation
dose limitation

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37
Q

what does justification mean in radiology?

A

must have sufficient benefit to individual or society to offset detriment

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38
Q

how do we optimise radiographs ?

A

ALARP
individual doses and people exposed should be As Low As Reasonable Practicable

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39
Q

dose optimisation is a legal requirement, how do we ensure dose is optimised?

A

ALARP
use rectangular collimators
use E speed film
kV range 60-70
focus to skin distance >200mm

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40
Q

circular collimators increase radiation dose by how much?

A

40%

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41
Q

how far should the controlled area extend from X-ray tube and patient?

A

1.5m

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42
Q

what are the two types of radiation effects?

A

deterministic
stochastic

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43
Q

what are deterministic effects of radiation?

A

tissue reactions
severity of effect is related to dose received
only occur above certain dose

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44
Q

what are stochastic effects of radiation?

A

probability of occurrence is related to dose received

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45
Q

when will you see deterministic effects of radiation?

A

several days after exposure

46
Q

what is a lethal dose of radiation?

A

6Sv to whole body

47
Q

stochastic effects can be subdivided into two categories, what are they and describe them?

A

somatic - disease or disorder e.g. cancer
genetics - abnormalities in descendants

48
Q

what are the possible consequences of radiation during pregnancy?

A

radiation exposure could damage or kill enough of the cells for embryo to resorb

49
Q

what dose of radiation will have lethal effects on an embryo immediately after implantation?

A

100mGy

50
Q

what dose of radiation will have lethal effects on an embryo during organogenesis?

A

> 250mGy

51
Q

what are some sources of natural background radiation?

A

radionuclides in air - radon gas 50%
cosmic rays 12%
external gamma radiation 13%
internal radionuclides from diet
air travel

52
Q

what is the estimated natural background radiation dose?

A

2.2mSv

53
Q

what is the lifetime risk of cancer of intra oral X-ray?

A

1 in 10 million-1 in 100 million - negligible risk

54
Q

what is the effective dose in intra oral x-rays?

A

0.005mSv

55
Q

what plate size would you use for anterior periapicals?

A

0

56
Q

4what plate side would you use for bitewings and posterior perioapicals?

A

2

57
Q

what plate size would you use for occlusal radiographs?

A

4

58
Q

digital images can be made more detailed, higher resolution and accurate by increasing what?

A

pixelation

59
Q

what are the disadvantages of higher pixelation?

A

each digital image will require more storage space so increased costs
limitations on how small pixels can be due to manufacturing challenges

60
Q

how many bits are radiographs typically processed in?

A

8
8 binary digits so 2 to power of 8 so 256 shades of grey

61
Q

what does PACS stand for?

A

picture archiving and communication system

62
Q

what is the purpose of identification dot on receptors?

A

to aid orientation

63
Q

give an example of digital x-ray receptors

A

phosphor plate
solid state sensor

64
Q

what are some advantages and disadvantages of phosphor plates?

A

thinner, lighter
wireless

latent image
variable room light sensitivity so risk of impaired image

65
Q

what are some advantages and disadvantages of solid state sensors?

A

no issues with room light control
more durable and replace less often

more expensive
bulkier and rigid
wired

66
Q

what’s inside an intra oral film packet?

A

radiographic film
protective paper - protects from light exposure, damage and saliva
lead foil to absorb excess X-ray photos
outer wrapper - prevents ingress of saliva

67
Q

what photons is radiographic film sensitive to?

A

x-ray photons and visible light photons

68
Q

what are the advantages of digital radiography?

A

no need for chemical processing
may storage and archiving
images can be integrated into patient records
easy transfer of images
can be manipulated

69
Q

what are the disadvantages of digital radiography?

A

worse resolution
requires diagnostic level computer monitors
risk of data corruption
hard copy generally lower image quality

70
Q

what are the advantages and disadvantages of self developing film?

A

no dark room or processing facilities required
faster

poorer image
image deteriorates
no lead foil
expensive

71
Q

what affects the reaction time of developing film?

A

time, temperature and concentration

72
Q

what are the potential causes of a pale image on film?

A

exposure issue - radiation exposure factors are too low

developing issue - film removed from solution too early
solution too cold or too dilute

opposite results in darker image

73
Q

film image is greenish yellow or milky, what has happened?

A

inadequate fixing meaning non-sensitised tissues are left behind

74
Q

what does the fixing process of film processing involve?

A

chemical reaction which removes non-sensitised crystals and hardens the remaining emulsion

75
Q

what is the structure of radiographic film?

A

transparent plastic base
adhesive attaches emulsion to plastic base
emulsion
protective coating of clear gelatin - sheilds emulsion

76
Q

what is radiographic emulsion composed of?

A

silver halide crystals embedded in a gelatin binder

77
Q

what is the equivalent of pixels in film radiography?

A

microscopic silver halide crystals

78
Q

how do silver halide (usually silver bromide) crystals react with x-ray?

A

become sensitised upon interaction with x- ray photons

79
Q

what happens to sensitised and non-sensitised crystals during the processing of film?

A

sensitised crystals are converted to particles of black metallic silver (dark parts)
non-sensitised crystals are removed (light parts)

80
Q

what are the fasted films in order of fastest to slowest?

A

F 20% faster than E
E twice as fast as D
D

81
Q

what is the purpose of intensifying screens?

A

used with indirect film to reduce radiation dose
but also reduce detail

82
Q

what does film processing do to the film?

A

converts it from latent invisible image to visible permanent image

83
Q

what are the steps of film development?

A

developing
washing
fixing
washing
drying

84
Q

what occurs during the developing stage of film processing?

A

converts sensitised crystals to black metallic silver particles

85
Q

what occurs during the fixing stage?

A

removes non-sensitised crystals and hardens the emulsion containing the black metallic silver

86
Q

what is the purpose of lead foil in the film packet?

A

absorbs some excess photons - those continuing past the film and those scattered by patient tissues

87
Q

what is the effect of film speed on radiation required to achieve an image?

A

increased speed means less radiation is required to achieve an image

larger crystals mean faster film but poorer image quality

88
Q

give examples of extra-oral radiographs

A

panoramic
cephalometric - lateral and posterior-anterior
oblique lateral

89
Q

direction of beam in lateral radiograph

A

side of head

90
Q

direction of beam in postero-anterior radiograph

A

starting posteriorly and passing anterior

91
Q

angulation of beam in oblique radiograph

A

not perpendicular to head

92
Q

angulation of beam in a true radiograph

A

perpendicular to head

93
Q

where is the Frankfurt plane?

A

infraorbital margin and superior border of internal auditory meatus

94
Q

how many degrees difference is there between orbitomeatal line and Frankfort plane?

A

10

94
Q

how many degrees difference is there between orbitomeatal line and Frankfort plane?

A

10

95
Q

where is the orbitomeatal line?

A

connects outer can this and centre of external auditory meatus

96
Q

what are the clinical applications of cephalometry?

A

orthodontics and orthognathic surgery
monitor changes
root length, locating un-erupted teeth

97
Q

what is a lateral cephalograph and what can be seen?

A

standardised true lateral radiograph
teeth, facial bones and soft tissues, sinuses

98
Q

cephalographs must be standardised and reproducible, how do we achieve this?

A

cephalostat - ensures standardised positioning of equipment and patients head

99
Q

what is the function of cephalostat?

A

to make cephalographs reproducible and standardised

100
Q

how does a cephalostat standardise radiographs?

A

avoids discrepancies between radiographs taken years apart
reduces magnification and distortion of image

includes ear rods and forehead support to hold head at correct angle and stabilise head

101
Q

what is the standardised distance between the receptor and x-ray focal spot for a cephalograph?

A

1.5m - 1.8m to reduce magnification

102
Q

soft tissues show up poorly when exposure settings are optimised for hard tissues, what is the solution?

A

use software to enhance soft tissues post-exposure
place aluminium wedge filter in unit to attenuate beam where it exposes soft tissues

103
Q

how do cephalographs meet ALARP legislation?

A

thyroid collar almost always
triangular collimation to reduce exposure of cranium
field of view should not be bigger than what is clinically required

104
Q

what are the two lateral extra oral radiographs in dentistry?

A

lateral cephalogram
oblique lateral

105
Q

what are the benefits of lateral oblique radiographs?

A

view of posterior jaws without superimposition of contralateral side
good if pt cannot tolerate intra-oral or won’t fit in OPT

106
Q

what are some indications of oblique lateral radiography?

A

pathology assessment
un-erupted teeth position
fractures
lesions e.g. tumours
poorly cooperative patients
involuntary movements

107
Q

how thin are slices on a CBCT?

A

0.4mm or thinner

108
Q

parallax horizontal tube shift options

A

2 periapicals
2 bitewings
2 oblique occlusifs

109
Q

parallax vertical tube shift options

A

panoramic and oblique occlusal
panoramic and lower periodical

BDS3 CDS (11 decks)

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