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Need to Know > radiology need to know > Flashcards

radiology need to know Flashcards

1
Q

what radiographs should be used to view retained roots?

A

periapical
OPT if poor pt cooperation

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2
Q

what is the bisecting angle technique?

A
  • x-ray beam at 90 degrees to line bisecting angle formed by the long axis of the tooth and the plane of film packet
  • image receptor and object partly in contact but not parallel
  • receptor and object close together except at paices
  • can be done without film holders
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3
Q

what is the parallel technique?

A
  • image receptor and object parallel but not in contact
  • divergent x-ray beam
  • image receptor and object some distance apart-potential for undesirable magnification
  • use long spacer cone to reduce magnification- 30cm
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4
Q

what is the purpose of the coin test?

A

to determine how long films can be exposed to safelight

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5
Q

what is the ideal projection geometry?

A
  • image receptor and object in contact and parallel
  • parallel beam of x-ray beam perpendicular to object plane and image receptor
  • image size identical to oject size
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6
Q

in an oblique radiograph, what lines are used for references and what are their positions?

A

maxilla- 1cm above ala-traguc line
mandible- through lower border of mandible

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7
Q

what are the oblique occlusal guideline vertical angles?

A
  • upper anterior- 60 degrees
  • upper occlusal centred on canine- 55 degrees
  • upper occlusal centred on premolar- 50 degrees
  • upper occlusal centred on molar- 45 degrees
  • lower occlusal- 40 degrees to occlusal plane
  • lower occlusal centred laterally- 35 degrees to occlusal plane
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8
Q

when would you use a mandibular true occlusal?

A
  • detection of submandibular duct calculi
  • assessment of bucco-lingual position of unerupted teeth- unless advanced imaging indicated
  • evaluation of pathological bucco-lingual expansion
  • horizontal displacement of fractures
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9
Q

why is rectangular collimation preferred?

A

has a greater dose reduction than circular

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10
Q

what are the 2 curves in bitewing radiographs?

A
  • curve of spee
  • curve of monson
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11
Q

describe the curve of spee

A
  • has antero-posterior direction
  • curves up posteriorly
  • produces a happy smile
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12
Q

describe the curve of monson

A
  • has a bucco-lingual direction
  • influences x-ray technique e.g. bitewings and panoramic radiography
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13
Q

what is cervical burnout?

A
  • relative lower x-ray absorption on mesial/distal aspect of teeth, between edge of enamel and adjacent to crest of alveolar ridge
  • these areas appear relatively radiolucent with ill-defined margins
  • may mimic root surface caries
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14
Q

what do panoramic radiographs show?

A
  • all teeth
  • structures above and below the teeth
  • structures superficial and deep to the teeth (provided they are close)
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15
Q

What is another term for the coin test?

A

Safelight testing

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16
Q

Explain the coin test

A

In the dark, place coins at intervals on an extra-oral film
Cover completely with card
Turn on safelights
Uncover each coin at intervals of 30 seconds, leaving the last coin covered
Process and observe which coin can be seen first

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17
Q

What causes ghost images?

A

When there is horizontal distortion if the patient is in the incorrect position to the focal plane

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18
Q

Name typical ghost images

A

Earrings
Metal restoration
Sodt tissue calcification
Soft palate
Hyoid bone
Dentures and fixed appliances

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19
Q

What are indications for an OPT?

A

When you require a full view of the dentition and surrounding structures including the TMJ and condyles
Fractures and evaluation of trauma
3rd molar relationship to ID canal on lowers
Bone loss in generalised periodontal disease
Large lesions that wouldn’t be seen on occlusal, bitewings or periapical
Retained/unerupted teeth and development of dentition
Developmental and acquired anomalies
TMJ evaluation
Inability to tolerate intra-oral radiographs

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20
Q

Name 3 positioning faults that can occur on a radiograph

A
  • Speed of beam through the teeth and image receptor through the beam must be synchronised to produce an accurate image
  • Patients canine must be synchronised behind the canine guide line which means it is closer to the x-ray source than the machine expects- cases speed of beam to be slower through the teeth as it is closer to the rotation centre- causes horizontal magnification
  • Patients canine in front of the canine guide line means it is further from the x-ray source than the machine expects- causes speed of beam to be faster through teeth as it is further from the rotation centre- image reduced horizontally
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21
Q

Name 2 forms of bone loss that can be seen on a radiograph

A

Horizontal
Vertical

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22
Q

Describe horizontal bone loss

A

Most common pattern of bone loss
Occurs when the path of inflammation is to the alveolar bone crest
Perpendicular to the tooth surface

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23
Q

Describe vertical bone loss

A

Less common pattern of bone loss
Occurs when the pathway of inflammation travels directly into the PDL spaces and occurs intra-orally

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24
Q

Name 3 characteristics of a ghost image

A
  • Will be present higher due to vertical beam angulation of bra
  • Horizontally magnified
  • Usually further forward due to change in antero-posterior position
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25
Q

Give 3 ways you can reduce the radiographic dose to the patient

A
  • Use of rectangular collimator combined with a beam-aiming device and film holder which reduces x-ray dose by 30%
  • Reducing the area irradiated and therefore volume irradiated will also reduce the number of scattered photons produced as well as patients dose
  • High tube kVp which produces higher energy photons meaning the photoelectric interactions and the contract between different tissues is reduced, meaning the dose absorbed by the patient also reduces
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26
Q

Describe the Compton effect

A
  • X-ray photon interacts with loosely bound over shell electrons
  • The photon energy is much greater than the electron binding energy
  • The electron is ejected, taking some of the photon energy as kinetic energy causing a recoil electron- this gives off an atom that is positively charged
  • Photon has lower energy after collision- now a scatter photon
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27
Q

What factors affect the probability of Compton scatter occurring

A
  • Proportional to density of material
  • Independent of atomic number
  • Not related to photon energy
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28
Q

Describe the photoelectric effect

A
  • X-ray photon interacts with inner shell electron- generally the k shell which has the highest energy
  • This photon has energy higher than the binding energy of the electron which makes the x-ray photon disappear
  • The difference in energy between the 2 levels is emitted as light and heat
  • Most of the energy used to overcome binding energy of the electron remainder gives electron kinetic energy meaning the electron is ejected as a photon -results in complete absorption of photon energy meaning the photon does not reach the film and preventing any interaction with component of the image receptor
  • Images appear white if all photos are involved
  • Images appear grey if some photons are involved
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29
Q

What factors affect the occurrence of the photoelectric effect

A
  • Atomic number
  • Photon energy
  • Density of material
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30
Q

What metal is used to absorb the jets generated during x-ray production?

A
  • Lead is used to prevent leakage
  • Lead film is for photoelectric absorption which absorbs scatter x-rays to prevent image degradation and its 2nd function is to absorb some of the primary beam
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31
Q

Name other metals used in x-ray production, other than lead

A
  • Zinc- prevents leakage in shielding
  • Aluminium and zinc- used for final spectrum of x-ray energy filtration
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32
Q

How are x-rays produced?

A

Produced when fast-moving electrons are brought rapidly to a stop

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33
Q

What are the 2 types of collimator used?

A

Rectangular
Circular

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34
Q

What is the maximum beam diameter of collimators?

A

60mm at the patient end with spacer cone

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35
Q

what plane should be horizontal to the floor whilst taking an OPT?

A

frankfort plane

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36
Q

what x-ray would you take for a patient who cannot tolerate bitewings?

A

OPT on setting 4

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37
Q

where is the Frankfort plane located?

A

lower border of orbit to the upper border of external auditory meatus

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38
Q

what are the limitations of a panoramic radiograph?

A
  • horizontal distortion
  • long exposure time not suitable for nervous pts or pts with additional needs
  • big shoulders
  • positioning difficulties
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39
Q

what is image processing?

A

the series of actions by which the invisible latent image is converted into a visible permanent image

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40
Q

why are films processed in a dark room?

A

to prevent light from affecting the films

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41
Q

what are the chemical processing steps when developing films?

A
  • development
  • rinse
  • fixation
  • washing
  • drying
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42
Q

what is attenuation?

A
  • reduction in the number of photons within th ebeam
  • occurs as a result of absorption and scatter
  • affects number of photons reaching film
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43
Q

how can you reduce the effects of scatter on the image?

A
  • increase the pt-film distance- obliquely travelling scattered photons miss the film
  • lead foil within the film packet prevents back scattered photons from oral tissues reaching film
  • collimation
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44
Q

what is the radiographic baseline?

A

outer canthus of the eye to centre of external auditory meatus

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45
Q

what is the difference between true and oblique lateral radiography?

A

oblique occlusal comes at an angle

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46
Q

what is IRMER?

A

ionising radiation medical exposure regulations

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47
Q

when would you use setting 4 on an OPT?

A
  • if focussing intraorally
  • this programme reduces overlap between teeth allowing easier interprox caries detection
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48
Q

when would you use setting 1 on an OPT?

A
  • if you want to see extra and intra oral
  • allows vision of eaxtra oral features such as TMJ and body of mandible
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49
Q

list oral implications of radiotherapy

A

xerostomia due to damage of salivary glands
increase risk of osteoradionecrosis
mucositis
radiation caries affecting incisal edges and cervical margins
limited opening due to trismus
hypogeusia

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50
Q

what position fault causes anterior teeth to appear magnified on a radiograph?

A

canine is positioned behind the canine guidance line

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51
Q

what position fault causes one side of the posterior region to appear wider than the other on a radiograph?

A

patient’s head rotated slightly in the OPT machine

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52
Q

in an OPT, what part of the maxillary sinus is immediately above premolars?

A

inferior border

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53
Q

in an OPT, what part of the maxillary sinus is immediately above the third molar?

A

posterior border

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54
Q

what x-ray would you use to determine working length?

A

periapical

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55
Q

what x-ray would you take for extraction of 48, with no sign of 38?

A
  • OPT of right side only, on setting 4
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56
Q

give features of a ghost image

A

image is always higher
the image is horizontally magnified
on theopposite side
can interfere with diagnosis

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57
Q

what are radiographic signs that a tooth is non-vital?

A

internal inflammatory resorption
external inflammatory resorption
periapical abscess
widened pdl
loss of lamina dura

58
Q

what position fault causes one side of the posterior region to appear wider than the other on a radiograph?

A

patient’s head rotated slightly in the OPT machine

59
Q

what are radiographic signs that a tooth is non-vital?

A

internal inflammatory resorption
external inflammatory resorption
periapical abscess
widened pdl
loss of lamina dura

60
Q

name complications of radiotherapy to the head and neck

A

mucositis
xerostomia
osteoradionecrosis
radiation induced caries

61
Q

What radiation dose increases the risk of osteoradionecrosis?

A

doses over 60 Gy

62
Q

What are oral complications of radiotherapy?

A

osteoradionecrosis
radiation caries
hypogeusia - loss of taste due to radiation affecting taste buds
xerostomia - may be due to damage of salivary glands
difficulty wearing dentures
more prone to fungal infections
trismus may occur due to replacement fibrosis of muscles of mastication

63
Q

what sites of the teeth are affected by radiation caries?

A

gingival margins and incisor edges

64
Q

what are causes of radiation caries?

A

dry mouth
loss of taste
change in diet
hypersensitivity of teeth makes OH difficult

65
Q

What do you need to know about patients who have had radiotherapy?

A

what dose of radiation was given
what area of the body was exposed to the radiation
duration of treatment

66
Q

What are preventative measures used for patients who have had radiotherapy?

A

OHI
higher concentration of fluoride toothpaste
fluoride varnish

67
Q

how do you treat osteoradionecrosis?

A

irrigation of necrotic debris
remove loose sequestra

68
Q

What methods help prevent risk of osteoradionecrosis?

A

scale teeth near extraction site and use chlorohexidine mouthwash
careful extraction technique
antibiotics, chlorhexidine mouthwash and review
hyperbaric oxygen before and after extraction to increase local tissue oxygenation
close soft tissues

69
Q

What is a wavelength

A

The distance over which the waves shape repeats

70
Q

what is frequency

A

how many times the waves shape repeats per unit time

71
Q

how do you calculate speed

A

frequency x wavelength

72
Q

what unit is energy measured in

A

electron volts eV

73
Q

how do you calculate intensity of the xray beam

A

1 / distance ^2

Double the distance you quarter the dose

74
Q

what metal is the focusing cup made of

A

molybdenum

75
Q

what is the charge of the cathode

A

negative

76
Q

What is the cathode composed of

A

filament and focusing cup

77
Q

what is the charge of the anode

A

positive

78
Q

what is the anode composed of

A

target and heat dissipating block

79
Q

what is the filament

A

a component of the cathode

a coiled metal wire that high current electricity is passed through

80
Q

what metal is the cathode filament made of

A

tungsten

81
Q

explain how the cathode works

A

increased current in the filament causes an increase in heat and increase in electrons

82
Q

explain the anode and cathode relationship

A

high potential difference between negative cathod and positive anode

high voltage electricity passed through the xray

electrons released by the filament are repelled by the cathode towards the target in the anode

electrons have a high kinetic energy when colliding with the anode target

83
Q

explain the kinetic energy of electrons between the anode and cathode

A

kinetic energy is gained as the electrons move from the cathode to the anode

if potential difference across xray tube is 70kV then each electron gains 70kV of kinetic energy when reaching the anode

84
Q

what is the target in the anode

A

the metal block bombarded by electrons producing photons and lots of heat

85
Q

what is the focal spot

A

precise area on target (anode) where electrons collide and xrays are produced

86
Q

wht metal is the target made of

A

tungsten

87
Q

what metal is the heat dissipating block made of and why

A

copper

it is a high thermal conductor - heat produced in the target dissipates into the block by thermal conduction which prevents target overheating

88
Q

what is the penumbra effect

A

blurring of radiographic image due to focal spot not being a single point

minimised by shrinking focal spot

89
Q

what happens if you decrease the focal spot size

A

increase image quality BUT increase heat concentration

90
Q

how do you solve the penumbra effect

A

angle target - reduces surface area where xray is emmitted

increases heat tolerance - increases surface where electrons impact

91
Q

what is the glass envelope and what is its function

A

leaded glass that produces an air tight enclosure

  • absorbs xray photons ensuring photons travelling in desired direction escape the xray tube
  • supports cathode and anode
  • maintains a vaccum
92
Q

why is aluminium in the tubehead important

A

it removes low energy photos from xray beam as the patients tissues would absorbing these and they don’t contribute to the image

this ensures xray beam contains of mainly diagnostic xray photons

93
Q

what is the function of the spacer cone

A

Dictates the distance between the focal spot (on target) and the patient

94
Q

what is the function of the lead collimator

A

reduces the patient dose

95
Q

what are the types of collimator and what is recommended to use/why?

A

circular
rectangular

rectangular can reduce the surface area and dose of radiation the patient receives

96
Q

what is continuous radiation

A

bombarding electron passes close to target nucleus causing it to be rapidly decelerated and deflected

lost kinetic energy release as xray photons - continuous range of energy

97
Q

what is characteristic radiation

A

bombarding electron collides with inner shell electron and either displaces is to a more peripheral shell or removes it completely

creates energy specific to the element used for target

98
Q

what is the k shell binding energy of tungsten

A

69.5 keV

remember dental xrays use 70kV to displace k shell electrons

99
Q

what is transmittion

A

photon passes through the matter unaltered

100
Q

What is absorption

A

photon is stopped by the matter

101
Q

what is scatter

A

the matter causes the photon to change direction

102
Q

what are the fates of photons in xrya beams

A

transmitted
absorbed
scattered and absorbed

this results in attenuation of the beam - reduced intensity

103
Q

explain attenuation in terms of colour of xrays

A

minimal attenuation - black
partial attenuation - grey
complete attenuation - white

104
Q

what is the photoelectric effect

A

photon interacts with inner electron shell - absorption of photon creating photoelectron

occurs when energy of photon is =/> binding energy of electron

inner shell electron is ejected (photoelectron) - this can ionise and damage adjacent tissues

vacancy in inner electron shell filled by outer shell electron producing light photons and/or heat

NECESSARY FOR IMAGE FORMATION

105
Q

what is the compton effect

A

photon interacts with outer shell - partial absorption and scattering of photon

occurs when energy of photon is > binding energy of electron

electron in outer shell removed (compton recoil electron) - this can ionise and damage adjacent tissues

remaining photon is scattered

DOESNT CONTRIBUTE TO IMAGE

106
Q

explain scatter for high energy photons

A

forward scatter

107
Q

explain scatter for low energy photons

A

back scatter

108
Q

what is implemented to account for radiation scatter

A

controlled area - 1.5m from patient

109
Q

how does scatter affect radiographic image

A

backwards and sideways - DO NOT affect the image

forward scatter - may reach receptor and interact with wrong area

causes darkening/fogging of image in the wrong place

reduces image quality/contrast

110
Q

what is the probability of photo electric absorption effects occuring in radiography is proportional to

A
  • atomic number cubed (Z3)!!
  • physical density of the material
  • inversely to photon energy cubed (1/E^3)
111
Q

give examples of how to reduce scatter

A

decrease surface area radiated
decrease volume of irradiated tissue
decrease number of scattered photons produced in the tissue
decrease the scattered photons interacting with the receptor

112
Q

what effect does lowering kV have on xray unit

A

increases contrast between tissues with different Z - GOOD

increases dose absorbed by patient - BAD

113
Q

what effect does raising kV have on the xray unit

A

decreases dose absorbed by patient - GOOD

decreases contrast between tissues with different Z - BAD

114
Q

what is the UK guidance range for kV

A

60-70kV

115
Q

what types of DNA damage can occur from radiation and explain them

A

direct - radiation interacts with the DNA molecule

indirect - radiation interacts with water in the cell producing free radical that causes damage

116
Q

explain how dose rate affects celss

A

higher dose - Cell cannot repair DNA damage

lower dose - cells can repair damage before further damage occurs

117
Q

what tissues are most radiosensitive

A

tissues with rapidly dividing cells

118
Q

what is the unit of measurement for equivalent dose

A

sieverts (Sv)

119
Q

what is the unit of measurement for absorbed dose

A

Gray (Gy)

120
Q

what are the two types of radiation biological effects and explain

A

deterministic - tissue reaction occurs above a certain threshold, severity related to the dose received

stochastic - the probability of occurence is related to dose received

121
Q

define justification in terms of radiology

A

practise must have sufficient benefit to the individual or society in order to offset the deteriment

122
Q

what are ways to reduce patient doses of radiation

A

use E speed film or faster
Use kV range of 60-70
focus skin distance should be >200mm
use rectangular collimation

123
Q

What does ALARP mean

A

as low as reasonably practicable

124
Q

what effects does radiation have on pregnancy

A
  • increased risk of childhood cancer
  • can retard growth
125
Q

what are DRLs

A

Diagnostic reference Levels - establish dose level for standard sized patients

126
Q

when is radiographic localisation used

A
  • locate position of unerupted teeth
  • location of roots
  • relationship of pathological lesions
  • trauma - bone or dental fracture
127
Q

what is the rule for parallax

A

same lingual opposite buccal

128
Q

what is a cephlostat and why is it important

A

standardised positioning of equipment and the patients head (ear rods and forehead support)

produces standardises and reproducible radiographs
reduce magnification/ distortion of image

129
Q

what is the collimation rule for all radiographs

A

field of view should be no bigger than what is clinically required

130
Q

how do pixels affect the xray image

A

more pixels = better detailed image

overall higher resolution

131
Q

what are the types of receptors used in digital intra oral radiographs

A

solid state sensors - connected to the computer/instant image

phosphor plates - put through a scanner

132
Q

why must you use adhesive plastic covers in radiology

A

to prevent saliva contamination
cross infection control

133
Q

what are advantages of digital radiology

A

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

134
Q

What are disadvantages of digital radiology

A

worse resolution
requires diagnostic level computer monitors for optimal viewing
risk of data corruption/loss
hard copy print outs have decreased image quality
image enhancement can create misleading images

135
Q

what is radiographic emulsion

A

silver halide crystals (silverbromide) in a gelatin binder - becomes pixels in the final image

sensitised crystals - dark parts of image.
non sensitised - light parts of image

136
Q

what affects film speed

A

number and size of silver halide crystals

137
Q

what are factors that cause issues in film radiology

A

developing - involves chemicals which are affected by time, temp and solution concentration

fixing - chemical reaction that remobes non-sensitised crystals

washing - developer continues to act if not washed off

138
Q

what are disadvantages of solid state sensors

A

bulkier
usually wired
expensive

139
Q

What causes the incisor teeth to be horizontally magnified in a panoramic

A

the patient is too far back in the machine

vertical guide line in front of canine

canine behind guide line

140
Q

what are radiographic signs a tooth is non vital

A

internal inflammatory resorption
external inflammatory resorption
periapical abscess
widened lamina dura
loss of lamina dura

141
Q

what are planes and reference lines used in radiology

A

mid saggital plane - line down the middle of face

interpupillary line - horizontal across pupils

Frankfort plane - inferior infraorbital margin to superior border eof external acoustic meatus

Orbitomeatal line - through middle of orbit

Need to Know (21 decks)

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