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radiology > 3rd year > Flashcards

3rd year Flashcards

1
Q

principles of radiation protection

A

justification
optimisation
dose limitation

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2
Q

optimisation

A

ALARP

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3
Q

dose limitation - who is it for?

A

radiation workers and public

not pts - by justifying you are saying that the dose is worth the benefit

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4
Q

source

A

x-ray machine

produces xrays

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5
Q

image receptor

A

digital - direct/indirect
film
screen-film combinations

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6
Q

processing

A

conversion of latent image into permanent visible image

digital or chemical

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7
Q

what energy source do xray machines use?

A

domestic electricity supply

converts to high voltage (to produce X-rays)

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8
Q

potential range

A

60-70kV (pan higher)

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9
Q

which part of the xray machine creates X-rays?

A

tube

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10
Q

what is a radiographic image?

A

pictorial representation of part of body
record of pattern of attenuation of xray beam after it has passed through matter
= absorption and scatter events

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11
Q

BWs include?

A

distal of canine posteriorly to include all CPs

one per side unless all premolars and molars

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12
Q

true (CS) occlusal

A

plan view of a section of mandible/FOM

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13
Q

2 types of occlusal

A

true

oblique

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14
Q

ceph

A

view of facial bones

incs ST profile

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15
Q

properties of xrays

A

senses: not perceptible
- need warning signals - sound (law), light
EM radiation
direction of travel
- straight, diverging beam
- inverse square law - area measured at end point larger the further you get from a source
photographic
interaction with matter
- no effect e.g. air
- complete absorption - white
- absorption and scatter - beam has its direction changed

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16
Q

ideal projection geometry

A

image receptor and object in contact and parallel
parallel beam of xrays
xray beam perpendicular to object plane and image receptor
- image size identical to object size

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17
Q

problems with projection geometry

A

image receptor and object not in contact
- tooth supported by bone so can’t contact all of it
beam of X-rays not parallel
- divergent
xray bean central ray may/may not be perpendicular to object plane and image receptor
image size not identical to object size due to magnification - divergent beam

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18
Q

projection geometry - 2 solutions

A

paralleling technique: image receptor and object parallel (but not touching)
bisecting angle technique: image receptor and object partially in contact, and not parallel to each other

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19
Q

paralleling technique

A

object and image receptor parallel so positioned some distance apart - not in contact
only central ray truly perpendicular - divergent beam

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20
Q

focus

A

where X-rays produced

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21
Q

short FSD

A

bad as produces extensive magnification of the image as diverging beam

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22
Q

FSD

A

where X-rays are produced to skin of pt

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23
Q

why should you use a long FSD?

A

reduce magnification as near parallel xray beam

at least 20cm

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24
Q

reasons for using film holders and BADs

A

dose reduction
better quality
fewer rejects so fewer retakes

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25
Q

components of film holders

A

bite block
BAD and rod
image receptor support

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26
Q

blue

A

anterior PAs

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27
Q

yellow

A

posterior PAs

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28
Q

red

A

BWs

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29
Q

green

A

endo

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30
Q

assembly of film holders

A

look through ring - should see image receptor support right in middle
if not then wrong - get ‘coning off’ - only part of image has radiograph

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31
Q

collimation

A

“restriction of CS area of beam”
controlling size and shape of xray beam, narrows it so less divergent
should be provided on new equipment and retro-fitted to existing equipment
circular or rectangular diaphragm

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32
Q

what material is used for collimation and why?

A

lead - v good at absorbing xrays

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33
Q

which type of collimation is ideal and why?

A

rectangular - 30% dose reduction compared to circular

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34
Q

curve of Spee

A

AP
curves up posteriorly
produces a happy smile

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35
Q

curve of Monson

A

BL

influences technique e.g. pan vertical angle is negative to occlusal plane -8 degrees

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36
Q

International Commission for Radiological Protection

A

international, independent, non-gov
recommendations and guidance on radiation protection
volunteer members

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37
Q

basic principles ICRP

A

justification
- sufficient benefit to individuals/society to offset any detriment
optimisation
- magnitude and number of persons exposed ALARP
dose limitation
- so no-one receives an unacceptable level of exposure

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38
Q

International Atomic Energy Authority

A

publish regulations based on ICRP - designed to be used as a template for radiation safety legislation globally
European Commission used it as a basis for Basic Safety Standards Directive
UK then required to put recommendations into law

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39
Q

what do IRR17 and IRMER17 come under?

A

HandS at work act

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40
Q

IRR17

A

occupational exposures and exposure of general public inc staff

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41
Q

IRMER17

A

medical exposures of patients (and some other groups)

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42
Q

who is IRR17 enforced by?

A

HSE

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43
Q

IRR17 employer and employee responsibilities

A

employer - responsible for compliance arrangements

employee - responsible for following safety arrangements

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44
Q

give some components of IRR17

A 
staff training
risk assessments
dose limitation - ALARP
dose limits
RPAs
RPSs
controlled areas
set of local rules
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45
Q

IRR17 licensing

A

employer must obtain registration from HSE for use of xrays
1 - answer Qs on compliance arrangements
2 - pay £25

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46
Q

IRR17 who is responsible for compliance?

A

NHS

private - owner responsible as employer

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47
Q

RPA

A

a person meeting HSE requirements to advise on radiation safety
- get certificate issued by ‘RPA2000’ (renew every 5yrs)

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48
Q

give some aspects that an employer should consult an RPA on

A

designation of areas
prior examination of plans for installations and acceptance into service of safety features and warning devices
regular equipment checks
periodic testing of safety features and warning devices
radiation risk and dose assessments
investigations
contingency plans

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49
Q

training for staff

A

basic radiation safety measures
ant specific requirements for that workplace
basic understanding of risks and awareness of regulations

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50
Q

annual radiation dose limits

A

radiation workers = whole body limit 6mSv/year (unclassified staff)
public = whole body limit 1mSv/year

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51
Q

carers and comforters

A

individuals ‘knowingly and willingly’ exposed to ionising radiation through support and comfort of those undergoing exposure
not doing so as part of their employment
often friends/relatives

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52
Q

Radiation risk assessment

A

what safety features are required?

what level of radiation exposure could staff receive?

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53
Q

controlled area

A

space nobody should be in while taking radiograph unless absolutely necessary

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54
Q

who will advise if need plasterboard/lead in walls?

A

RPA

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55
Q

IO controlled area

A

1.5m from xray tube and within primary beam

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56
Q

CBCT controlled area

A

entire room

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57
Q

controlled area regulations

A 
need signage
 - entire room
 - entrance leads directly in
set off local rules
appoint RPS to oversee arrangements
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58
Q

who enforces IRMER17?

A

HIS

inspectors

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59
Q

who does IRMER17 apply to?

A 
pts as part of diagnosis/tx
health screening
research
asymptomatic individuals
carers and comforters
individuals undergoing non-medical imaging using medical equipment
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60
Q

RPS

A

ensures regulations and training are followed

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61
Q

non-medical imaging using medical radiological equipment which does not confer a health benefit to the individual exposed

A 
health assessment
 - employment
 - immigration
 - insurance
radiological age assessment
identification of concealed objects within body
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62
Q

Employer’s procedures

A

set out how regulations are complied with
14 procedures
- pt identification
- entitlement of staff
- info provided to pts e.g. poster - benefits and risks

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63
Q

duty holders

A

referrer
practitioner
operator
employer

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64
Q

referrer

A

refer for imaging

clinically justify, pt details

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65
Q

practitioner

A

justification (and authorisation)
benefits vs risks
no recent radiographs
ALARP

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66
Q

operator

A

(authorise)
check pt demographics, ALARP, takes exposure, processes and reports
anyone who carries out practical aspects that can affect pt dose

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67
Q

employer

A

legal person, safety
make sure equipment in line with IRR99
staff follow regs

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68
Q

what is justification based on?

A

history and clinical exam

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69
Q

process of justification

A 
info from referrer, consider:
objectives of exposure, efficacy, benefits and risks of available alternative techniques
benefits (diagnostic/therapeutic)
 - individual
 - society
detriment to individual
characteristics of individual involved

justify then authorise - record

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70
Q

justification can be a 2 step process

A

written justification guidelines prepared by practitioner

authorisation as justified by operator at time of exposure

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71
Q

justification - refer back to referrer

A

insufficient info

not justified

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72
Q

clinical evaluation

A

legal requirement
each exposure outcome
- can’t be justified if known a CE won’t be performed
Referrer’s responsibility

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73
Q

medical physics expert

A

advice on exposure factors and equipment-related matters

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74
Q

optimisation

A 
IRMER17 
ALARP
responsibility - Practitioner and Operator
considerations
 - investigations and equipment
 - exposure factors
 - QA
 - assessing pt dose
 - adherence to DRLs
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75
Q

QA of radiation equipment

A

test regularly
- working
- expected dose level
routine local tests - staff who normally operate equipment
physics tests - every 1-3yrs by specialist staff

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76
Q

which legislations outline tests required and recommended freq?

A

IPEM 91
CoR
NRPD

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77
Q

DRLs

A

guideline dose levels for “standard sized” pts undergoing typical exams
can use as a benchmark against local and national practice
some equipment displays ‘dose indicator’ after exposure - compare against DRL
checked during QA tests
risk assessments used to evaluate control measures§

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78
Q

occlusal radiographs IR

A

7x5cm

3x4 size 2 PA in children

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79
Q

which arch are true CS occlusals taken for?

A

lower

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80
Q

oblique occlusal indications

A

PA type assessment where PA not possible = trismus/gag
pathology too large to be seen on a single PA
- bigger IR, can see all 4 incisors
trauma - fractures
- easier to bite gently than on hard plastic PA
localisation using parallax

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81
Q

bisecting angle technique

A

IR and object partly in contact but not parallel
IR and object close together at crowns but apart at apices
- distance depends on part of mouth

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82
Q

do you need IR holders for bisecting angle technique?

A

no

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83
Q

bisecting angle technique - vertical angle selection

A

bisect angle between long axis and image receptor
central ray at 90 degrees to bisector - correct length of image
correct due to identical triangles

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84
Q

bisecting angle technique - xray beam at 90 degrees to LA of tooth

A

elongated image

vertical angulation too small

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85
Q

bisecting angle technique - xray beam at 90 degrees to plane of IR

A

foreshortened image

vertical angulation too large

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86
Q

bisecting angle technique - how much image receptor beyond incisal edge?

A

2-3mm

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87
Q

bisecting angle technique - how is the angle adjusted to adapt to the incisor angulation?

A

proclined - increase

retroclined - decrease

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88
Q

head position for maxillary occlusal

A

ala-tragus line parallel to floor

for a seated upright pt

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89
Q

head position for mandibular occlusal

A

corner of mouth - tragus line parallel to floor

for a seated upright pt

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90
Q

centring point

A

where the central ray enters the body

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91
Q

what should the horizontal angle be?

A

90 degrees to line of arch to avoid overlaps

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92
Q

centring points - PAs

A

maxilla - on ala-tragus line

mandible - 1cm above lower border of mandible

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93
Q

centring points - oblique occlusals

A

maxilla - 1cm above ala-tragus line (collimator just above bridge of nose)
mandible - through lower border of mandible

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94
Q

how are PP protected?

A

cardboard/plastic

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95
Q

what does the orientation of IR depend on?

A

size of mouth and pt tolerance

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96
Q

oblique occlusals - guideline vertical angles

A

upper anterior (standard) - 60
occlusal centred on canine 55
premolar 50
molar 45
lower anterior occlusal 40 (to occ plane)
lower occlusal centred laterally 35

teeth become more upright as go back to molars - why you drop by 5 each time

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97
Q

indications for a mandibular true occlusal

A

detection of SM duct calculi
- concentric growth or conforms to duct

    • unless advanced imaging indicated
  • assessment of BL position of UE teeth
  • evaluation of pathological BL expansion
  • horizontal displacement of fractures

nowadays more CBCT

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98
Q

true/CS occlusal

A

occlusal or PA size IR
plan view
when beam is through LA of a tooth
only do L jaws - get a poor image for upper

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99
Q

mandibular true occlusals positioning

A

IR transverse in occlusal plane OR lengthwise over region of interest
head tipped back as far as is comfortable
x-ray beam directed at 90 degrees to IR in midline or through region of interest

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100
Q

errors in pan radiography

A 
pt prep
exposure
positioning
processing
film handling
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101
Q

DPT

A

method of radiography displaying details of a selected plane (layer/slice) within the body

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102
Q

image layer/focal trough

A

a layer in the pt that contains structures of interest that are demonstrated with sufficient resolution to make them recognisable, whilst structures at other depths (superficial and deeper) are not clearly seen
contains all teeth, structures above and below
- close superficial and deep
- distant structures not clear

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103
Q

impact of different size perimeters i.e. distance from rotation centre

A

further from the rotation centre the faster the beam passage around the circumference

larger circle equivalent to further from rotation centre = faster speed

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104
Q

linear tomography - principle of layer formation

A

xray source L to R
receptor R to L
objects not in focal plane projected to continually changing points on film
object in focal plane projected onto same point of film

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105
Q

what makes layer formation happen

A

movement of xray source (therefore beam) through teeth

movement of receptor through xray beam at the correct speed so desirable objects (teeth etc) will be recorded as clear images

objects outside the desired layer will be portrayed as either distorted unsharp images, or be imperceptible

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106
Q

layer position and speeds - posterior teeth

A

posterior teeth further from their rotation centre

  • faster beam passage through teeth
  • IR movement also fast to match
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107
Q

layer position and speeds - anterior teeth

A

anterior teeth closer to their rotation centre

  • slower beam passage through teeth
  • IR movement becomes slower to match and prevent distortion
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108
Q

xray beam panoramic

A

vertical narrow beam
passes through pt from lingual to buccal
xray tube head rotates around back of pt
xray beam angled upwards at -8 (due to curve of Monson)
IR rotates around front of pt, and passes through xray beam

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109
Q

panoramic - movement

A

wavy lower border of mandible

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110
Q

ghost images - common objects

A

earrings
metal Rxs
anatomical features - esp opp side of mandible
ST calcifications e.g. LNs, salivary calcification

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111
Q

what happens to the rotation centre?

A

it changes continuously

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112
Q

what does the distance from rotation centre to teeth affect?

A

with of layer in focus/focal trough
horizontal distortion if pt in incorrect position relative to machine focal trough
ghost images

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113
Q

what is the width of the focal trough/layer in focus dependent on?

A

width of xray beam - same throughout
distance to rotation centre
- closer to rotation centre (anteriors) = narrower layer
- further away (posteriors) = wider layer

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114
Q

pan limitations

A

pts occlusion
long exposure time (up to 16s)
big shoulders
if you can’t see it, it doesn’t mean its not there - width of layer in focus
horizontal distortion
positioning difficulties
narrow width in focus anteriorly - miss some

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115
Q

about ghost images

A

always higher due to - vertical beam angulation -8 degrees
always horizontally magnified
change in AP position - usually further forward
can interfere with diagnosis - but not always

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116
Q

formation of ghost images

A

xray tube start position directs beam posteriorly towards opposite TMJ region
tube moves round behind pts’ head
when image of premolar region is centred beam is coming from a more posterior point on opp side
ghost images usually more anterior than real image

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117
Q

EO dose reduction in pan

A

collimation - pan programme selection
rare earth screens: system speed 400 or greater
digital

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118
Q

IO dose reduction

A

60-70kV
rectangular collimation
E or F speed film
digital

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119
Q

pan - what must be synchronised to produce an accurate image?

A

speed of beam through teeth and IR through beam

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120
Q

pan magnified horizontally

A

pts C behind C guide line (closer to xray source than machine expects)
speed of beam slower through teeth as closer to rotation centre
if not compensated, IR too fast and image magnified horizontally

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121
Q

pan reduced in width horizontally

A

pts C in front of CGL (further from xray source than machine expects)
speed of beam faster through teeth as further from rotation centre
- if not compensated, IR too slow and teeth reduced in width horizontally

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122
Q

pan uses

A 
development of dentition
pathological jaw lesions
mandibular fractures
developmental and acquired abnormalities
surgery = evaluation and review
(caries, pulpal, PDD)
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123
Q

EM radiation

A

flow of energy created by simultaneously varying electrical and magnetic fields - schematically represented as a sine wave (up and down movement in its energy)
travels as “packets” of energy known as photons

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124
Q

properties of EM radiation

A

no mass
no charge
travels at speed of light 3 x10⁸ ms-1
can travel in a vacuum

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125
Q

freq

A

cycles/secs Hz

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126
Q

EM spectrum

A

different properties dependent on energy, wavelength, frequency
- same type of radiation

gamma, xray, UV, visible, IR, microwave, radiowave

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127
Q

radiowave

A

longer WL
lower freq
lower energy

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128
Q

gamma ray

A

shorter WL
higher freq
higher energy

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129
Q

amplitude

A

distance from midline

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130
Q

freq definition

A

how many times the wave’s shape repeats per unit time
Hz
- 1 = 1 cycle/sec

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131
Q

wavelength

A

the distance over which the wave’s shape repeats itself

m

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132
Q

speed equation

A

speed = freq x wavelength
BUT speed of all photons is constant 3x10⁸ms-1
so if freq increases then WL must decrease and vv
energy directly proportional to freq

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133
Q

photon energy

A

EM radiation involves the movement of energy as photons

eV

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134
Q

1eV

A

enery (in J) gained by one electron moving across a potential difference of 1V

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135
Q

properties of xrays

A

form of EM radiation
undetectable to human senses
man-made
- y rays identical except that they occur naturally (and generally have higher energies)
cause ionisation
- what causes damage to human tissues
- i.e. displacement of electrons from atoms/molecules

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136
Q

The atom (Bohr model)

A 
nucleus
 - protons.  +.    1. 
 - neutrons. neural.   1
shells (orbiting)
 - electrons. -       negligible (0)
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137
Q

electron shells

A

electrons spin around the nucleus in discrete orbits/shells
- cannot exist between these shells
innermost shell K, then L, M, N, O etc
e-s try to fill spaces available in inner shells first

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138
Q

why are X-rays called this?

A

because of their unknown nature

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139
Q

xray photon energies

A

124eV to 124KeV

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140
Q

hard xrays

A

higher energies

able to penetrate human tissues

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141
Q

soft xrays

A

lower energies

easily absorbed

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142
Q

what type of X-rays does medical imaging mostly use?

A

hard X-rays e.g. >5KeV

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143
Q

basic production of xrays

A

can use tungsten
electrons fired at atoms at v high speed
on collision, the KE of these electrons is converted to EM radiation (ideally X-rays) and heat (side product)
xray photons aimed at a subject

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144
Q

nucleus

A

collection of nucleous

  • protons and neutrons have similar mass
  • overall + charge
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145
Q

atomic number (Z)

A

number of protons

unique to each element

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146
Q

mass number (A)

A

P + N

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147
Q

max number of e- in each shell

A

2n²

- shell number

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148
Q

how are orbiting electrons held in their shell?

A

by electrostatic force

negative charge of electrons attracted to + nucleus

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149
Q

number of electrons

A

determines chemical properties of an atom

“ground state” - neutral e=p

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150
Q

ionisation

A

removing or adding e

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151
Q

binding energy

A

additional energy required to overcome the electrostatic force and remove an e from its shell

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152
Q

increased binding energy

A

closer e to nucleus = greater electrostatic force and therefore binding energy
- K shell highest BE
more positively charged nucleus (i.e. higher Z) greater electrostatic force

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153
Q

what happens if you lose an electron from an inner shell?

A

an outer shell e will move in

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154
Q

formula to remove an e

A

if the energy input ≥ BE

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155
Q

current

A

flow of electric charge, usually by the movement of e

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156
Q

SI unit for charge

A

amp, A

- measure of how much charge flows past a point per sec

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157
Q

two directions of current

A

DC
AC
as long as the e are moving you will be producing energy

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158
Q

DC

A

constant unidirectional flow e.g. batteries

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159
Q

AC

A

flow repeatedly reverses direction
number of complete cycles (reverse and reverse back) per unit time is the freq
SI unit is Hz (cycles per sec)

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160
Q

voltage

A

difference in electrical potential between 2 points in an electrical field
related to how forcefully/fast a charge (e) will be pushed through an electrical field

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161
Q

SI unit voltage

A

Volt, V

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162
Q

potential difference

A

voltage

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163
Q

electron movement between shells

A

the specific amount of energy required to move an e to a more outer shell = the difference in BEs of the 2 shells

if an e drops to a more inner shell then this specific amount of energy is released
- possibly in the form of xray photons (if sufficient energy)

164
Q

dental xray unit components

A 
tubehead
collimator
positioning arm
control panel
circuitry
165
Q

mains electricity supply

A

AC

220-240V

166
Q

rectification of current

A

xray production requires a unidirectional current
- but xray units are powered by mains electricity (AC)
have generators which modify the AC so that it mimics a constant DC
- rectification

167
Q

dental xray unit electricity requirements

A

DC (rectification)
requires 2 different voltages
- one as high as 10000s V (firing electrons fast)
- one as low as 10V (create electrons to be fired)

168
Q

transformers

A

alter the voltage (and current) from one circuit to another

169
Q

2 separate transformers required for xray unit

A

mains to xray tube (cathode - anode)

mains to filament

170
Q

step-up transformer

A

increase potential difference across xray tube
usually 60-70kV
current reduced to mA

171
Q

step-down transformer

A

reduce potential difference across filament
10V
10amps

172
Q

xray beam intensity

A

quantity of photon energy passing through a CS area of the beam per unit time
increase number and/or energy of photons = increased intensity
proportional to current in filament (mA) and PD across xray tube (kV)

173
Q

a particles

A

stopped by paper

174
Q

B particles

A

stopped by Al

175
Q

y rays

A

reduced by thick lead

176
Q

how are a, B, y different to X-rays?

A

all produced by radioactive decay of unstable atoms - unlike X-rays which are directly man-made

177
Q

xray beam

A

made up of millions of xray photons directed in the same general direction
photons effectively travel in straight lines but diverge from the xray source - do not travel in parallel

178
Q

divergence of xray beam

A

dose decreases with distance from xray source - beam diverges so not all xray photons irradiating them

179
Q

inverse square law

A

intensity of xray beam is inversely proportional to the square of the distance between the xray source and the point of measurement
intensity proportional to 1/distance squared

so doubling the distance will quarter the dose

180
Q

when are X-rays produced?

A

when fast moving electrons are rapidly decelerated

181
Q

xray tube head components

A 
filament - cathode
transformer
target - anode
target surround
evacuated glass envelope (shielding)
filtration
collimator
spacer cone
182
Q

filament - cathode

A

negative
tungsten
filament circuit (step-down transformer): low voltage, high current

183
Q

tungsten

A

W
Z = 74
mp 3410 degrees - can reuse and it won’t disintegrate/melt - it will retain its integrity

184
Q

filament function

A

cathode
low voltage current passed through filament circuit
filament heats up to incandescence
e form a cloud around filament

185
Q

operating potential

A

new equipment should operate within range 60-70kV

affects

  • how X-rays will interact with matter
  • pt dose
186
Q

transformer - why hollow centre?

A

so X-rays can go through it so they don’t interact with it

187
Q

step-up transformer process

A

240eV domestic input
60-70KeV high voltage output
huge attraction of e (mA) from cathode towards anode (target)
flow of e about 7-15mA
want to pull e over towards positive side of xray tube - need high V

188
Q

target - anode

A

positive
tungsten
effective area 0.7mm²
20 degree slope i.e. not parallel to filament - increases efficiency
referred to also as a focus or focal spot

189
Q

target interactions

A

heat production 99% - inefficient
xray production <1%
- continuous spectrum (energy output)
- characteristic spectrum (characteristic to tungsten - material where interactions are happening)

190
Q

target interactions - xray production: continuous spectrum

A

incoming e passes close to nucleus of a target atom
e rapidly decelerated and deflected
amount of deceleration and deflection proportional to E loss
E loss in the form of EM radiation has a continuous spectrum of energies
max E is applied kV e.g. 70

191
Q

what is continuous spectrum also known as?

A

Bremstrahlung/braking/white radiation

192
Q

target interactions: heat production

A

incoming e
- deflected by a cloud of outer shell tungsten e or collides with an outer shell e displacing it
small loss of energy (E) - in the form of HEAT

removed through copper block, oil then air

193
Q

target surround

A

tungsten target set into a block of copper which is v good at conducting heat away
copper Z = 29 mp = 1080 degrees - effective heat conductor

194
Q

why are low energy X-rays not useful?

A

don’t have enough energy to get through the tissues and produce an image

195
Q

describe the appearance of the graph for continuous spectrum of xray energies

A 
number of photons (intensity) - y axis
photon energy (KeV) - x axis
straight line decreasing (linear) to 70
196
Q

characteristic spectrum of tungsten xray energies

A

characteristic radiation of tungsten has values of approx

  • 8kV - L shell
  • 58kV - K shell
  • 68kV - K shell
197
Q

filtration

A

get rid of low energy X-rays that you don’t want

198
Q

material used for filtration

A

Al Z = 13

  • high energy X-rays will get through
    1. 5mm ≤ 70kV
    2. 5mm > 70kV
199
Q

what does the spacer cone do?

A

control the target FSD

200
Q

where is FSD measured between?

A

external marker and pt end of cone

201
Q

FSD distances

A

100mm <60kV

200mm ≥ 60kV

202
Q

target interactions - xray production - characteristic spectrum

A

incoming e collides with an inner shell target e
target e displaced to an outer shell or completely lost from atom
target atom unstable
orbiting e rearranged to fill vacant orbital slots to return atom to neutral state
difference in E between orbits is released as characteristic radiation, of known E values
same mechanism as PE absorption

203
Q

glass envelope

A

evacuated glass

vacuum prevents risk of interaction of electrons with air atoms prior to meeting target

204
Q

shielding

A

lead Z=82
- high atomic no means good absorber of X-rays
to ensure dose rate in vicinity not >7.5u Sv h -1

205
Q

collimator

A

lead
circular or rectangular diaphragm
max bean diameter 60mm at pt end of spacer cone

206
Q

what does a long FSD reduce?

A

magnification

207
Q

xray photons traversing tissue may:

A

pass through unaltered - no energy loss
change direction with no energy loss (scatter)
change direction losing energy (scatter and absorption)
be stopped, depositing all energy within tissue (absorption)

208
Q

production of a radiographic image

A

xray photons pass from tube, and some through pt to reach image receptor
interaction with different tissues alters number of photons exiting pt
- diff spread of energy levels
variation in number of photons reaching IR produces radiographic appearance of different tissues

209
Q

attenuation

A

reduction in number of photons (X-rays) within beam
occurs as a result of absorption and scatter
affects number of photons reaching IR

210
Q

effect of photon absorption on image

A

all photons reach film - black
partial attenuation - grey
complete attenuation - white

211
Q

principal interactions of diagnostic X-rays in tissue

A

photoelectric effect - absorption

Compton effect - scatter and absorption

212
Q

what does PE effect result in?

A

complete absorption of photon energy - photon does not reach film

213
Q

PE effect

A

xray photon interacts with inner shell e (usually K)
photon has energy just higher than the binding energy of electron
- only happens if this is true
xray photon disappears
most of photon energy is used to overcome BE of e, remainder gives e KE
electron is ejected (photoelectron)
atom has ‘hole’ in electron shell: + charge
ionised atom is unstable
e drops from outer shell, filling void
diff in energy between 2 levels is emitted as light/heat (characteristic radiation)
- to the elements and the shells
outer voids filled by ‘free’ e

214
Q

effect of PE absorption on image

A

complete absorption of photon
prevents any interaction with active component of IR
image appears white if all photons involved, grey if some photons not involved

215
Q

occurrence of PE absorption proportional to:

A

atomic number cubed (Z³)
1/photon energy³ (1/kV³)
density of material

216
Q

PE absorption - atomic numbers and cubes

A

relatively small differences in Z result in large differences in PE absorption
- good differentiation between tissues

217
Q

Compton effect - first stage

A

xray photon interacts with loosely bound outer shell e
photon energy considerably greater than e BE
e ejected taking some of photon energy as KE: recoil e
atom is then positively charged

218
Q

Compton effect - what happens to excess energy in the original photon?

A

following collision, photon has lower energy (longer wavelength)
called a scatter photon
undergoes a change of direction - related to how much energy it has lost

219
Q

Compton effect - following scatter events

A

atomic stability regained by capture of free electron
recoil electron can interact with other atoms in tissue
scatter photon, dependent on energy and position of bound electron involved, can be involved in more Compton or PE interactions

220
Q

Compton effect - what happens to scattered photons?

A

can travel in any direction
direction of scatter is affected by energy of scatter photon
- high energy - forward direction
- backward direction - low energy
full range of directions between the two extremes dependent on energy

221
Q

probability of Compton effect occurring

A

proportional to density of material (e density)
independent of atomic number
not related to photon energy, although forward scatter more likely with high energy photons

222
Q

effect of Compton scattered photons

A

scattered photons produced before the IR is reached, and scattered backwards, do not reach IR and do not contribute to the image
scattered photons produced beyond IR, and scattered back towards it, may reach IR producing darkening
- as their path is randomly altered they do not contribute useful info to the image
- results in fogging (general increased darkness) of image, reducing contrast (between adjacent materials) and image quality

223
Q

reduction of scatter - methods

A

collimation - reduce area and vol irradiated

  • reduce number of scattered photons produced as well as reducing pt dose
  • smallest area compatible with diagnostic outcomes

lead foil within film packet prevents back scattered photons from oral tissues reaching film (also absorbs some of energy in primary beam)
- not used with digital receptors - inherently more sensitive so use lower dose anyway

224
Q

effect of PE absorption on dose

A

deposition of all photon energy within tissue - increases pt dose but necessary for image quality

225
Q

effect of Compton scatter on dose

A

deposition of some photon energy within tissue
adds to pt dose but doesn’t give useful info
may increase dose to operators (only if standing too close to pt)

226
Q

effect of high kVp on image quality and pt dose

A

high tube kVp produces higher energy photons
PE interactions are reduced
contrast is reduced
dose absorbed by pt is reduced

no point reducing dose so much that image is of no diagnostic quality

227
Q

absorption of photons more likely if:

A

object traversed has a high atomic number
object traversed is thicker
photon energy is lower

228
Q

radiographic contrast

A

difference in density in light and dark areas of radiograph

image showing both light and dark areas with clear borders - high contrast - ideal

229
Q

when is contrast greatest?

A

when difference in absorption by adjacent tissues is greatest

230
Q

effect of low kVp on image quality and pt dose

A

low tube potential difference (kVp) produces lower energy photons
PE interactions are increased
contrast between different tissues increases
BUT dose absorbed by pt is increased

231
Q

what is the chosen kVp a compromise between?

A

diagnostic quality of the image and dose

60-70kV

232
Q

a particle

A

2p/2n
large particle, travels a few inches
most damaging type of radiation

233
Q

B-particle

A

e-

v small particle, travels a few feet

234
Q

y-ray

A

EM
high energy
travels long distances

235
Q

ionising radiation

A

atoms have e=p, ions don’t
ionising radiation has enough energy to turn atoms into ions
- “knocks” away e orbiting the nucleus of an atom

236
Q

interaction of radiation with tissues

A

when radiation passes through matter - ionises atoms along its path
each ionisation process will deposit a certain amount of energy locally, around 35eV
- greater than the energy involved in atomic bonds (4eV)

237
Q

single strand break in DNA

A

can usually be repaired

238
Q

double strand DNA breaks

A

more difficult to repair
usually result of a radiation
if the repair is faulty - can lead to mutations which can affect cell fct

239
Q

factors affecting the biological effect of DNA damage

A

type of radiation
amount of radiation (dose)
time over which the dose is received (dose rate)
tissue or cell type irradiated

240
Q

what is the most significant effect of ionising radiation?

A

damage to DNA

241
Q

evidence of DNA damage

A

can be seen in faulty repair of chromosome breaks

242
Q

direct effect DNA damage

A

radiation interacts with atoms of a DNA molecule or another important part of the cell

243
Q

indirect effect DNA damage

A

radiation interacts with water in the cell, producing free radicals which can cause damage
free radicals are unstable, highly reactive molecules

244
Q

dose survival curves

A

low doses of radiation produce less damage

linear relationship for a particles, which in turn kills more cells than a similar dose of X-rays would

245
Q

dose rate

A

radiation delivered at a low dose rate is less damaging
cells can repair less serious DNA damage before further damage occurs
at high dose rates, the DNA repair capacity of the cell is likely to be overwhelmed

246
Q

possible outcomes after radiation hits a cell nucleus

A 
no change
DNA mutation
 - mutation repaired - viable cell
 - cell death - unviable cell
 - cell survives but is mutated - cancer?
247
Q

dose quantities - tissue cancer risk

A

following large radiation exposures - higher incidences of cancer in certain tissues
most medical exposures do not irradiate the body uniformly
- risk will vary depending on organ that receives the highest dose

248
Q

what is tissue radio sensitivity dependent on?

A

the fct of the cells that make up the tissues

if the cells are actively dividing - the more rapidly a cell is dividing the greater the sensitivity to radiation

249
Q

SCs and tissue radiosensitivity

A

exist to produce cells for another cell pop - divide freq, v radiosensitive

250
Q

differentiated cells and tissue radiosensitivity

A

do not exhibit mitotic behaviour, less sensitive to radiation damage

251
Q

highly radiosensitive tissues

A 
bone marrow
lymphoid tissue
GI
gonads
embryonic tissues
252
Q

moderately radiosensitive tissues

A

skin
vascular endothelium
lungs
lens of eye

253
Q

least radiosensitive tissues

A

CNS
bone and cartilage
CT

254
Q

dose

A

measure of amount of energy that has been transferred and deposited in a medium

255
Q

why have additional dose units been defined?

A

to quantify the level of biological damage and the overall effect of the dose

256
Q

severity of ionising radiation

A

effect of ionising radiation on tissue is greater than would be expected from amount of energy involved

257
Q

what might heavily damaged cells be programmed to do?

A

die

258
Q

absorbed dose

A

measures the energy deposited by radiation
Gy

= but different types of radiation can cause different levels of damage to tissues

259
Q

equivalent dose

A

absorbed dose multiplied by a weighting factor depending on the type of radiation
B, y and X-rays - 1
a particles - 20
Sv

260
Q

equivalent dose units

A

Sv

261
Q

absorbed dose units

A

Gy

262
Q

what does the LNT model estimate?

A

the long term biological damage from radiation

263
Q

LNT model assumptions

A

damage directly proportional (linear) to radiation dose
radiation always harmful with no safety threshold
response linearity - several small exposures would have same effect as one large exposure
the effective dose is directly proportional to the risk of cancer

264
Q

deterministic effects

A

tissue reactions
can only occur above a certain (threshold) dose
severity of the effect is related to the dose received
unusual to see in radiology although possible in high dose areas e.g. interventional radiology
often effects won’t show immediately but several days after exposure
e.g. erythema, tissue damage, skin injury

265
Q

stochastic effects

A

no known threshold - no dose below which the effects will not occur
cannot predict if these effects will occur in an exposed individual or how severe they will be
- likelihood of the effect occurring increases as the dose increases
effects can develop years after exposure

266
Q

lethal dose

A

6Sv to whole body

267
Q

subdivision of stochastic effects into 2 categories

A

somatic - disease/disorder e.g. cancer

genetics - abnormalities in descendants

268
Q

pregnant pts

A

don’t need to take into account for dental X-rays because the dose to the foetus is so low
foetus must not be irradiated inadvertently nor should the xray beam be directed towards pts abdo
- if this is unavoidable then a protective lead apron (0.25mm) must be worn

269
Q

effects of radiation during early pregnancy

A 
radiation exposure could damage/kill enough of the cells for the embryo to undergo resorption 
lethal effects induced by doses of 100mGy before or immediately after implantation of the embryo into the uterine wall
during organogenesis (2-8wks post-conception) when the organs are not fully formed, doses >250mGy could lead to growth retardation
doses for these abnormalities are >1000x greater than an IO
270
Q

sources of natural background radiation

A 
cosmic rays
internal radionuclides from diet
radionuclides in air e.g. radon 
external y radiation e.g. soil, rocks and building materials
air travel
271
Q

estimated annual background radiation dose

A

2.2mSv

272
Q

UK pop split of natural and artificial radiation

A

84% natural (50% of this radon gas)

16% artificial

273
Q

IO xray effective dose

A

0.005mSv
lifetime risk of cancer 1 in 10m to 1 in 100m
negligible risk

274
Q

protection of staff - dose limits to body

A

employee 20mSv
U18 trainee 6mSv
other 1mSv

275
Q

protection of staff - controlled area

A

should extend at least 1.5m from the xray tube and pt

xray beam should always be directed away from staff

276
Q

dose optimisation

A 
ways to reduce pt dose
use E speed film or faster (fewer xray photons required)
use a kV range of 60-70kV
FSD >20cm
rectangular collimation
277
Q

images with minor artefacts or non-uniformities should be saved

A

refer to these if suspected artefact in clinical image

can also be used for training purposes

278
Q

CBCT

A

sectional images

thin slices, usually 0.4mm or thinner

279
Q

DRLs

A

established dose levels for typical examinations for standard sized pts
a comparative standard that is used in optimisation compared to NRLs
individual xray units compared to DRLs and NRLs
- identify units giving higher doses

280
Q

current DRLs for IO exams - adult

A
  1. 9mGy digital

1. 2mGy PP and film

281
Q

current DRLs for IO exams - child

A
  1. 6mGy digital

0. 7mGy PP and film

282
Q

what do digital and film radiography differ in?

A

how the xray beam is dealt with after it has interacted with the pt
ie how it is captured, converted into an image, stored

283
Q

size 0

A

ant PAs

284
Q

size 2

A

BWs, post PAs

285
Q

size 4

A

occlusals

286
Q

receptors

A 
digital
 - PP
 - SSS
film
 - direct action film
 - indirect action film
287
Q

conversion of xray shadow into image

A

when xray beam passes through an object some of the xray photons are attenuated “xray shadow”
image “info” held by photons after an xray beam has passed through an object
image receptor detects this xray shadow and uses it to create an image

288
Q

digital radiography - xray shadow to digital image

A

detector measures the xray intensity at defined areas (arranged in a grid)
each area given value relating to xray intensity
- typically 0-255
- 0 - high intensity
each value corresponds to a different shade of grey
- 0 = black
- 255 = white

289
Q

the digital image

A

displayed as a grid of squares - pixels
each pixel can only display one colour at a time
the more pixels you have the more detailed/accurate your image can be

290
Q

number of pixels

A

more pixels = better detail = higher resolution
will provide a more diagnostic image up to a limit
- eventually will not provide any meaningful clinical benefit
need more storage space - increased costs
digital receptors limited in now small they can make the pixels because of manufacturing issues (film - substrate of microscopic crystals - don’t have to create a grid)

291
Q

greyscale bit depth

A

radiographs typically processed in at least 8 bits
refers to the number of different shades of grey available
8 binary digits = 2⁸ = 256 shades of grey

292
Q

manipulating digital images

A 
software can be used to copy, resize and alter images
contrast/windowing
negative
emboss
magnify
293
Q

management of digital images: PACS

A

Picture Archiving and Communication System
storage and access to images
archives for storage and retrieval

294
Q

viewing digital radiographs

A 
env - subdued lighting, avoid glare
monitor
 - clean
 - adequate display resolution
 - high enough brightness level
 - suitable contrast level
295
Q

format for digital images - DICOM

A

Digital Imaging and Communications in Medicine
international standard format for handling digital medical images
- used to transmit, store, retrieve, print, process and display images
essentially alternative to jpeg etc
allows imaging to work between diff software, machines, manufacturers, hospitals and countries without compatibility issues
stores other important data alongside image e.g. pt ID, exposure settings, date

296
Q

SMPTE test pattern

A

Society of Motion Picture and Television Engineers

can be used to assess the resolution, contrast and brightness of your monitor

297
Q

types of digital IO receptor

A

SSS e.g. CMOS sensor

PP e.g. PSP plates

298
Q

PP after taking xray

A

not connected to a computer

after receptor is exposed to xrays it must be put in a scanner and ‘read’ to create final image

299
Q

image creation using PPs - in mouth

A

receptor exposed to xray beam

phosphor crystals in receptor excited by the xray energy - create a latent image

300
Q

image creation using PPs - in scanner

A

receptor scanned by a laser
laser energy causes the excited phosphor crystals to emit visible light
light is detected and creates visible image

(phosphor plate scanners are connected to computer)

301
Q

types of SSS

A

CCD (charge-coupled device)

CMOS (complimentary metal oxide semi-conductor)

302
Q

SSS creation of image

A

connected to computer
- usually wired but can be wireless
latent image created and immediately read within the sensor itself
- final image created virtually instantly

303
Q

SSS components

A 
back housing and cable
electronic substrate
CMOS imaging chip
fibre-optic face plate
scintillator screen
front housing
304
Q

SSS - CMOS imaging chip

A

light converted to electrical signals

305
Q

SSS - scintillator screen

A

emits light when xrays hit

306
Q

identification dot

A

located in corner of receptor to aid orientation of image
only effective if receptor was positioned correctly during exposure
BWs - dot to top
PAs - dot towards crown

307
Q

cross-infection control

A

IO receptors have single use covers to prevent saliva contamination e.g. adhesive sealed plastic covers for PPs, long plastic sleeves for wired SSSs
receptor still disinfected between uses
need to dry after disinfect - bubbles on receptor will show on image

308
Q

why should you hold receptor by edges not by flat surfaces?

A

scratches/tears
fingerprints
bending/creases

309
Q

importance of careful handling

A

certain types of damage will impact every subsequent image obtained from that receptor
- reduce diagnostic value and may render receptor unusable

310
Q

advantages of PPs

A

thinner and lighter
(usually) flexible - good if limited mouth opening - can bend a bit going into mouth
wireless - more stable and comfortable

311
Q

disadvantages of PPs

A

variable room-light sensitivity
- risk of impaired image
- left in sunlight too long can bleach sensor
latent image needs to be processed in scanner separately
handling similar to film

312
Q

SSS disadvantages

A

bulkier and rigid
usually wired
sealer active area (for same physical area of receptor)
£££

313
Q

SSS advantages

A

no issues with room light control - light can’t get through hard plastic
arguably more durable - replaced less often

314
Q

components of radiographic film packet

A

protective black paper
lead foil
outer wrapper
film

315
Q

components of radiographic film packet - protective black paper

A

protects film from light exposure, damage by fingers and saliva

316
Q

components of radiographic film packet - lead foil

A

absorbs some excess xray photons - not contributing to image, will just enter pt and cause damage

317
Q

components of radiographic film packet - outer wrapper

A

prevents ingress of saliva

indicates which side of the packet is the front

318
Q

components of radiographic film packet - film

A

material in which the actual image is formed
sensitive to both xray photons and visible light photons
photons interact with emulsion on film to produce latent image which only becomes visible after chemical processing

319
Q

radiographic film structure

A

transparent plastic base
adhesive
emulsion
protective coating of clear gelatin

320
Q

radiographic film structure - transparent plastic base

A

supports the emulsion

321
Q

radiographic film structure - adhesive

A

attaches the emulsion to the plastic base

322
Q

radiographic film structure - emulsion

A

layered on both sides of the plastic base
silver halide crystals embedded in a gelatin binder (usually silver bromide)
microscopic crystals
what become the ‘pixels’ of the final image
- film generally higher resolution than digital

323
Q

radiographic film structure - protective coating of clear gelatin

A

shields the emulsion from mechanical damage

324
Q

film - silver halide crystals mechanism of action

A

usually silver bromide
become sensitised upon interaction with xray (and visible light) photons
- change slightly and become excited
during processing - sensitised crystals converted to particles of black metallic silver (dark parts of final image)
non-sensitised crystals removed (light parts of final image)

325
Q

film speed

A

relates to amount of xray exposure required to produce an adequate image
increased speed - reduced radiation required to achieve an image

326
Q

what is film speed affected by?

A

number and size of silver halide crystals

- larger crystals - faster film but poorer image quality

327
Q

what film speed should be used?

A

the fastest film which still provides satisfactory images

328
Q

comparing E and D film

A

E is twice as fast as D

  • therefore requires half exposure time - half radiation dose
  • most commonly used film
329
Q

comparing E and F film

A

F is 20% faster than E
- 20% reduction in exposure time (and dose)
requires automated processing - not everyone has this in practice

330
Q

if changing to a different film speed must either:

A

convert settings on xray unit (by a qualified technician)

install a filter to absorb part of the primary xray beam

331
Q

lead foil

A

in packet, lying behind the film
absorb some excess xray photons
- those in primary beam continuing past the film
- those scattered by pts tissues and returning back to film
embossed pattern to highlight (on image) if receptor was placed wrong way round
- embossed so you don’t think too low exposure used and you repeat

332
Q

what are intensifying screens used alongside?

A

special “indirect action” film for EO radiographs e.g. pan, ceph
- too bulky for IO use

333
Q

effect of intensifying screens

A

reduce radiation dose

but reduce detail - slightly fuzzier as it is being spread out by the cone of visible light

334
Q

why are intensifying screens becoming less commonplace?

A

digital receptors more common

335
Q

how intensifying screens work

A

“indirect action” film placed inside cassette with an intensifying screen on either side
screens release visible light upon exposure to xrays - this visible light creates latent image on film
- designed only to interact with visible light photons

336
Q

film processing

A

steps which convert the invisible latent image to a permanent visible image
need controlled, standardised conditions to ensure consistent image quality

337
Q

methods of film processing

A

manual
automated
(self-developing)

338
Q

film processing common steps

A 
1 - developing 
2 - washing
3 - fixing
4 - washing
5 - drying
339
Q

film processing step 1

A

developing

converts sensitised crystals to black silver particles

340
Q

film processing step 2

A

washing

removes residual developer solution

341
Q

film processing step 3

A

fixing
removes non-sensitised crystals
hardens emulsion (which contains the black silver)

342
Q

film processing step 4

A

washing

removes residual fixer solution

343
Q

film processing step 5

A

drying

removes water so that film is ready to be handled/stored

344
Q

manual (wet cycle) - what happens?

A

person dips film into different tanks of chemicals

  • at precise concs/temps
  • for specific times
  • washes film after each tank
345
Q

manual (wet) cycle requirements

A

dark room with absolute light-tightness

adequate ventilation

346
Q

how long does manual (wet) cycle take?

A

about 20mins

347
Q

difference in steps between manual and automated cycle

A

extra washing step in manual

in automated - sponge rollers squeeze developer solution out of film (instead of washing with water)

348
Q

automated cycle

A 
machine
exposed film goes in at one end = processed film comes out the other
developer
fixer
wash
dryer
349
Q

pros and cons of automated cycle

A

faster (5mins)
more standardised/controlled than manual
avoids need for dark room
more £££

350
Q

opening a film packet for automated processing

A

disinfect surface of packet and wipe off
hold packet under hood of process or unit
peel back flap of outer wrapper
fold back lead foil
pull back paper flap
hold film by edges (not surfaces) and slide out
insert film into processer slot/shelf

351
Q

self-developing films

A

not recommended

give tube a squeeze and the chemicals go up to where the film is

352
Q

self-developing films pros

A

no darkroom or processing facilities required

faster e.g. 1min

353
Q

self-developing films cons

A 
poorer image quality
image deteriorates more rapidly over time
no lead foil
easily bent
difficult to use in positioning holders
relatively £
354
Q

potential causes of pale image

A 
exposure issue
 - radiation exposure factors too low
developing issue
 - film removed from solution too early
 - solution too cold
 - solution too dilute/old
(opp will result in dark)
355
Q

processing issues - washing

A

developer and fixer solution will continue to act if not washed away/off

  • fixer - looks like bubbles
  • developer - black spots
356
Q

film storage

A

takes up room
- have to keep films for 11yrs for medico-legal
need to be accessible and safe from damage
require a reliable organisation system
- to allow images to be found easily
- to reduce risk of images being lost/mixed up

357
Q

processing issues - developing

A

chemical reaction
- sensitised silver halide crystals to black silver (oxidised in air)
reaction affected by time, temp and solution conc
developer solution oxidises in air
- becomes less effective over time
- needs to be replaced regularly (irrespective to how many films have been developed)

358
Q

processing issues - fixing

A

chemical reaction - removes non-sensitised crystals and hardens the remaining emulsion
inadequate fixing - non-sensitised crystals left behind
- image greenish-yellow or milky
- image becomes brown over time

359
Q

advantages of digital

A 
no need for chemical processing
easy storage and archiving of images
easy back-up of images
images can be integrated into pt records if digital
easy transfer/sharing of images
images can be manipulated
360
Q

disadvantages of digital

A

worse resolution - risk of pixelation
- digital perfectly good nowadays
requires diagnostic-level computer monitors for optimal viewing
risk of data corruption/loss (solved by backing up)
hard copy print outs generally worse quality
image enhancement can create misleading images

361
Q

caries diagnosis methods

A 
visual - smooth and occlusal
radiography
elective temporary tooth separation 
FOTI
electrical methods
laser fluorescence
calcivis - detects Ca2+ loss from demineralising tooth surfaces
362
Q

caries clinically vs on radiograph

A

always larger clinically than on radiograph

363
Q

cervical burnout

A

phenomenon caused by relative lower xray absorption on the M/D aspect of teeth, between the edge of the E and the adjacent crest of alveolar ridge
B-L dimension of tooth less at IP area - diff amount of xray energy getting through
because of the relative diminished xray absorption, appear relatively radiolucent with ill-defined margins
may mimic root surface caries
- should be detectable clinically
exposure-dependent
saucer-shaped radiolucencies

364
Q

PD assessment - selection criteria recommendations

A

radiography secondary to clinical exam and full mouth PD assessment
pocketing 4-5mm: horizontal BWs
pocketing ≥6mm: vertical BWs and PAs if bone not shown
irregular: may supplement with PAs
panoramic useful for overview of all teeth, supplemented by PAs if required or full PAs
PAs for suspected endo-perio lesions

365
Q

which wall of MS don’t you see on a pan?

A

lat wall (see post wall)

366
Q

PD radiography techniques

A

if pan chose orthogonal projection (P4)
beam angulation crucial
horizontal angle 90 degrees to line of arch
- avoids overlaps of adjacent teeth
vertical angle 90 degrees to LA of tooth
pockets may be difficult to show - consider GP point
clinical pocket depth exam crucial

367
Q

EO radiography definition

A

xray source and IR outside pt

368
Q

lateral radiography types

A

true

oblique

369
Q

true lateral radiography

A

film and MSP are parallel and xray beam is perpendicular to both

370
Q

oblique lateral radiography

A

film and MSP are not parallel

xray beam is not perpendicular to either, but oblique to both

371
Q

OM line

A

RBL

outer canthus of eye to centre of EAM

372
Q

Frankfort plane

A

superior border EAM to lowest point of IO rim

373
Q

difference between RBL and FP

A

10 degrees

374
Q

cephalometric radiography

A

standardised and reproducible form of skull/facial bones radiography
used in ortho
lateral or PA projections

375
Q

indications for lat ceph

A 
orthognathic surgery 
 - pre-op assessment and post-op review
implant planning - historically
 - anterior mandible - CS image
 - now often CBCT
376
Q

lat ceph distances

A

source to pts MSP = 152.4cm (5ft) in traditional equipment

image receptor to MSP: manufacturer dependent, fixed or adjustable

377
Q

effect of anode-object distance on magnification

A

longer - less difference in magnification as less divergent xray beam

378
Q

lateral views

A

lat ceph
lat oblique (mandible)(OJ)
- only shows you one side of pt
bimolar - both sides on one receptor

379
Q

lat ceph

A

true lateral view of facial bones, base of skull and upper cervical spine
also shows paranasal sinuses and nasopharyngeal STs

380
Q

ortho radiographs - lat ceph

A

pts with skeletal vertical or AP discrepancy
need fixed/fct appliance therapy, for labiolingual movement of incisors
requiring orthognathic surgery and ortho
- do CBCT now instead don’t do both

381
Q

set up of lat ceph equipment

A

cephalostat (free standing/attached to pan machine)
ear rods
CCD/CMOS sensor or cassette holder (PP or intensifying screens)
(anti-scatter grid - but higher dose to pt - not often used)

382
Q

lat ceph collimation

A

height and depth of field of view or triangular - adjustable, by programme or visual

383
Q

positioning and preparation for lat ceph

A

select
press button to line up xray tube head and cephalostat with receptor
hinge nasion rest up and sideways, nasion marker
thyroid collar on
FP horizontal
MSP vertical and parallel to casette
MSP correct distance from cassette if adjustable
teeth together - in centric occlusion or as requested
ear rods in EAM - move symmetrically
nasion support in space
programme selection (height and width adjustment) or move triangular collimation
automatic exposure adjustment or Al ST filter, preferably pre-pt
magnification scale
automatic facial contour in direct digital machines OR Al wedge filter - ideally at tube head
- allow you to see STs?

384
Q

why can successive lat ceps be used to analyse changes?

A

fixed distances so subsequent images will always be able to be directly comparable

385
Q

oblique lateral

A

film and MSP not parallel
xray beam not perpendicular to either MSP or film
EO view of jaws - R and L sides separately
uses dental or EO xray set
limited use now due to pan

386
Q

indications for lateral oblique

A

generally same as for pan but particularly when pan not available or possible e.g. handicapped pt
no longer done at GDH

387
Q

subjective quality rating - excellent

A

no errors of pt prep, exposure, positioning or film handling

target >70%

388
Q

subjective quality rating - diagnostically acceptable

A

some errors
does not detract from diagnostic utility
target <20%

389
Q

subjective quality rating - unacceptable

A

errors make film diagnostically unacceptable
needs retaken
target <10%

390
Q

reject analysis

A

unacceptable radiographs and reasons why?

may be multiple errors - don’t stop looking when you find one

391
Q

what must PA contain?

A

must contain full length of roots
ideally full crown - but not critical as can examine it clinically
bone around the roots

392
Q

what must BWs contain?

A

from mesial of first premolar distally to last tooth
U and L teeth equally
critical - to see ADJ
desirable - no overlap
- but some overlap (as long as you can see ADJ) doesn’t make it 3

393
Q

QA - prev dental guidance notes definition

A

to ensure consistently adequate diagnostic info whilst radiation doses are controlled to be ALARP
“the establishment of procedures, at every stage of image formation and utilisation, to ensure optimum image quality and max acquisition of info”

394
Q

QA - stages involved

A

selection criteria - right view when needed
production of xrays - correct kV
image geometry - film holders with BAD
image receptor - fastest film/digital
image processing - test tool
image viewing - light box or monitor quality
reject analysis

395
Q

coning off

A

incorrect film holder assembly or collimator orientation

396
Q

density variation

A

exposure factors
object factors
processing factors
viewing facilities

397
Q

monitoring processing

A

process test film daily

compare with reference film

398
Q

reference film options

A

clinical film
standard object e.g. extracted tooth
ideal object e.g. Al or Pb step foil wedge - test tool and film - use BW exposure, in contact
wooden spatula

399
Q

darkroom and daylight loading processors

A 
cleanliness
stock control - organisation
light tightness - room and cassettes
safelights - coin test
replenishment
400
Q

quality of original - viewing conditions

A

dim room
transmitted light restricted to film
film sensitive to xrays and pressure

401
Q

image viewing influenced by:

A

quality of original
equipment
env
knowledge base

402
Q

dark crescents

A

nail pressure

403
Q

safelight testing

A

need to ensure processing in safe env that doesn’t damage the film
in dark, place coins at intervals on an EO film
cover completely with card
turn on safelights
uncover each coin
- at 30/10s intervals, leaving last coin covered
- which is the first coin to be seen

404
Q

elongated teeth - occ and PAs

A

error is decreased vertical angulation - how the beam is related to the occ plane

405
Q

shortened teeth - occ and PAs

A

error is increased vertical angulation

406
Q

pale IO image

A

too long fsd or inadequate development (development creates the dark bits)

407
Q

IRR99 - 5 advised safety features

A 
controlled area
warning sign for controlled area
sign lights up when equipment on
light and audible sound during exposure
exposure with continuous pressure only
exposure stops automatically

radiology (5 decks)

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