3rd year Flashcards
(407 cards)
1
Q
principles of radiation protection
A
justification
optimisation
dose limitation
2
Q
optimisation
A
ALARP
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
4
Q
source
A
x-ray machine
produces xrays
5
Q
image receptor
A
digital - direct/indirect
film
screen-film combinations
6
Q
processing
A
conversion of latent image into permanent visible image
digital or chemical
7
Q
what energy source do xray machines use?
A
domestic electricity supply
converts to high voltage (to produce X-rays)
8
Q
potential range
A
60-70kV (pan higher)
9
Q
which part of the xray machine creates X-rays?
A
tube
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
11
Q
BWs include?
A
distal of canine posteriorly to include all CPs
one per side unless all premolars and molars
12
Q
true (CS) occlusal
A
plan view of a section of mandible/FOM
13
Q
2 types of occlusal
A
true
oblique
14
Q
ceph
A
view of facial bones
incs ST profile
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
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
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
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
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
20
Q
focus
A
where X-rays produced
21
Q
short FSD
A
bad as produces extensive magnification of the image as diverging beam
22
Q
FSD
A
where X-rays are produced to skin of pt
23
Q
why should you use a long FSD?
A
reduce magnification as near parallel xray beam
at least 20cm
24
Q
reasons for using film holders and BADs
A
dose reduction
better quality
fewer rejects so fewer retakes
25
components of film holders
bite block
BAD and rod
image receptor support
26
blue
anterior PAs
27
yellow
posterior PAs
28
red
BWs
29
green
endo
30
assembly of film holders
look through ring - should see image receptor support right in middle
if not then wrong - get 'coning off' - only part of image has radiograph
31
collimation
"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
32
what material is used for collimation and why?
lead - v good at absorbing xrays
33
which type of collimation is ideal and why?
rectangular - 30% dose reduction compared to circular
34
curve of Spee
AP
curves up posteriorly
produces a happy smile
35
curve of Monson
BL
| influences technique e.g. pan vertical angle is negative to occlusal plane -8 degrees
36
International Commission for Radiological Protection
international, independent, non-gov
recommendations and guidance on radiation protection
volunteer members
37
basic principles ICRP
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
38
International Atomic Energy Authority
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
39
what do IRR17 and IRMER17 come under?
HandS at work act
40
IRR17
occupational exposures and exposure of general public inc staff
41
IRMER17
medical exposures of patients (and some other groups)
42
who is IRR17 enforced by?
HSE
43
IRR17 employer and employee responsibilities
employer - responsible for compliance arrangements
| employee - responsible for following safety arrangements
44
give some components of IRR17
```
staff training
risk assessments
dose limitation - ALARP
dose limits
RPAs
RPSs
controlled areas
set of local rules
```
45
IRR17 licensing
employer must obtain registration from HSE for use of xrays
1 - answer Qs on compliance arrangements
2 - pay £25
46
IRR17 who is responsible for compliance?
NHS
| private - owner responsible as employer
47
RPA
a person meeting HSE requirements to advise on radiation safety
- get certificate issued by 'RPA2000' (renew every 5yrs)
48
give some aspects that an employer should consult an RPA on
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
49
training for staff
basic radiation safety measures
ant specific requirements for that workplace
basic understanding of risks and awareness of regulations
50
annual radiation dose limits
radiation workers = whole body limit 6mSv/year (unclassified staff)
public = whole body limit 1mSv/year
51
carers and comforters
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
52
Radiation risk assessment
what safety features are required?
| what level of radiation exposure could staff receive?
53
controlled area
space nobody should be in while taking radiograph unless absolutely necessary
54
who will advise if need plasterboard/lead in walls?
RPA
55
IO controlled area
1.5m from xray tube and within primary beam
56
CBCT controlled area
entire room
57
controlled area regulations
```
need signage
- entire room
- entrance leads directly in
set off local rules
appoint RPS to oversee arrangements
```
58
who enforces IRMER17?
HIS
| inspectors
59
who does IRMER17 apply to?
```
pts as part of diagnosis/tx
health screening
research
asymptomatic individuals
carers and comforters
individuals undergoing non-medical imaging using medical equipment
```
60
RPS
ensures regulations and training are followed
61
non-medical imaging using medical radiological equipment which does not confer a health benefit to the individual exposed
```
health assessment
- employment
- immigration
- insurance
radiological age assessment
identification of concealed objects within body
```
62
Employer's procedures
set out how regulations are complied with
14 procedures
- pt identification
- entitlement of staff
- info provided to pts e.g. poster - benefits and risks
63
duty holders
referrer
practitioner
operator
employer
64
referrer
refer for imaging
| clinically justify, pt details
65
practitioner
justification (and authorisation)
benefits vs risks
no recent radiographs
ALARP
66
operator
(authorise)
check pt demographics, ALARP, takes exposure, processes and reports
anyone who carries out practical aspects that can affect pt dose
67
employer
legal person, safety
make sure equipment in line with IRR99
staff follow regs
68
what is justification based on?
history and clinical exam
69
process of justification
```
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
70
justification can be a 2 step process
written justification guidelines prepared by practitioner
| authorisation as justified by operator at time of exposure
71
justification - refer back to referrer
insufficient info
| not justified
72
clinical evaluation
legal requirement
each exposure outcome
- can't be justified if known a CE won't be performed
Referrer's responsibility
73
medical physics expert
advice on exposure factors and equipment-related matters
74
optimisation
```
IRMER17
ALARP
responsibility - Practitioner and Operator
considerations
- investigations and equipment
- exposure factors
- QA
- assessing pt dose
- adherence to DRLs
```
75
QA of radiation equipment
test regularly
- working
- expected dose level
routine local tests - staff who normally operate equipment
physics tests - every 1-3yrs by specialist staff
76
which legislations outline tests required and recommended freq?
IPEM 91
CoR
NRPD
77
DRLs
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§
78
occlusal radiographs IR
7x5cm
| 3x4 size 2 PA in children
79
which arch are true CS occlusals taken for?
lower
80
oblique occlusal indications
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
81
bisecting angle technique
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
82
do you need IR holders for bisecting angle technique?
no
83
bisecting angle technique - vertical angle selection
bisect angle between long axis and image receptor
central ray at 90 degrees to bisector - correct length of image
correct due to identical triangles
84
bisecting angle technique - xray beam at 90 degrees to LA of tooth
elongated image
| vertical angulation too small
85
bisecting angle technique - xray beam at 90 degrees to plane of IR
foreshortened image
| vertical angulation too large
86
bisecting angle technique - how much image receptor beyond incisal edge?
2-3mm
87
bisecting angle technique - how is the angle adjusted to adapt to the incisor angulation?
proclined - increase
| retroclined - decrease
88
head position for maxillary occlusal
ala-tragus line parallel to floor
| for a seated upright pt
89
head position for mandibular occlusal
corner of mouth - tragus line parallel to floor
| for a seated upright pt
90
centring point
where the central ray enters the body
91
what should the horizontal angle be?
90 degrees to line of arch to avoid overlaps
92
centring points - PAs
maxilla - on ala-tragus line
| mandible - 1cm above lower border of mandible
93
centring points - oblique occlusals
maxilla - 1cm above ala-tragus line (collimator just above bridge of nose)
mandible - through lower border of mandible
94
how are PP protected?
cardboard/plastic
95
what does the orientation of IR depend on?
size of mouth and pt tolerance
96
oblique occlusals - guideline vertical angles
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
97
indications for a mandibular true occlusal
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
98
true/CS occlusal
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
99
mandibular true occlusals positioning
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
100
errors in pan radiography
```
pt prep
exposure
positioning
processing
film handling
```
101
DPT
method of radiography displaying details of a selected plane (layer/slice) within the body
102
image layer/focal trough
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
103
impact of different size perimeters i.e. distance from rotation centre
further from the rotation centre the faster the beam passage around the circumference
larger circle equivalent to further from rotation centre = faster speed
104
linear tomography - principle of layer formation
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
105
what makes layer formation happen
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
106
layer position and speeds - posterior teeth
posterior teeth further from their rotation centre
- faster beam passage through teeth
- IR movement also fast to match
107
layer position and speeds - anterior teeth
anterior teeth closer to their rotation centre
- slower beam passage through teeth
- IR movement becomes slower to match and prevent distortion
108
xray beam panoramic
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
109
panoramic - movement
wavy lower border of mandible
110
ghost images - common objects
earrings
metal Rxs
anatomical features - esp opp side of mandible
ST calcifications e.g. LNs, salivary calcification
111
what happens to the rotation centre?
it changes continuously
112
what does the distance from rotation centre to teeth affect?
with of layer in focus/focal trough
horizontal distortion if pt in incorrect position relative to machine focal trough
ghost images
113
what is the width of the focal trough/layer in focus dependent on?
width of xray beam - same throughout
distance to rotation centre
- closer to rotation centre (anteriors) = narrower layer
- further away (posteriors) = wider layer
114
pan limitations
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
115
about ghost images
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
116
formation of ghost images
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
117
EO dose reduction in pan
collimation - pan programme selection
rare earth screens: system speed 400 or greater
digital
118
IO dose reduction
60-70kV
rectangular collimation
E or F speed film
digital
119
pan - what must be synchronised to produce an accurate image?
speed of beam through teeth and IR through beam
120
pan magnified horizontally
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
121
pan reduced in width horizontally
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
122
pan uses
```
development of dentition
pathological jaw lesions
mandibular fractures
developmental and acquired abnormalities
surgery = evaluation and review
(caries, pulpal, PDD)
```
123
EM radiation
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
124
properties of EM radiation
no mass
no charge
travels at speed of light 3 x10⁸ ms-1
can travel in a vacuum
125
freq
cycles/secs Hz
126
EM spectrum
different properties dependent on energy, wavelength, frequency
- same type of radiation
gamma, xray, UV, visible, IR, microwave, radiowave
127
radiowave
longer WL
lower freq
lower energy
128
gamma ray
shorter WL
higher freq
higher energy
129
amplitude
distance from midline
130
freq definition
how many times the wave's shape repeats per unit time
Hz
- 1 = 1 cycle/sec
131
wavelength
the distance over which the wave's shape repeats itself
| m
132
speed equation
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
133
photon energy
EM radiation involves the movement of energy as photons
| eV
134
1eV
enery (in J) gained by one electron moving across a potential difference of 1V
135
properties of xrays
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
136
The atom (Bohr model)
```
nucleus
- protons. +. 1.
- neutrons. neural. 1
shells (orbiting)
- electrons. - negligible (0)
```
137
electron shells
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
138
why are X-rays called this?
because of their unknown nature
139
xray photon energies
124eV to 124KeV
140
hard xrays
higher energies
| able to penetrate human tissues
141
soft xrays
lower energies
| easily absorbed
142
what type of X-rays does medical imaging mostly use?
hard X-rays e.g. >5KeV
143
basic production of xrays
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
144
nucleus
collection of nucleous
- protons and neutrons have similar mass
- overall + charge
145
atomic number (Z)
number of protons
| unique to each element
146
mass number (A)
P + N
147
max number of e- in each shell
2n²
| - shell number
148
how are orbiting electrons held in their shell?
by electrostatic force
| negative charge of electrons attracted to + nucleus
149
number of electrons
determines chemical properties of an atom
| "ground state" - neutral e=p
150
ionisation
removing or adding e
151
binding energy
additional energy required to overcome the electrostatic force and remove an e from its shell
152
increased binding energy
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
153
what happens if you lose an electron from an inner shell?
an outer shell e will move in
154
formula to remove an e
if the energy input ≥ BE
155
current
flow of electric charge, usually by the movement of e
156
SI unit for charge
amp, A
| - measure of how much charge flows past a point per sec
157
two directions of current
DC
AC
as long as the e are moving you will be producing energy
158
DC
constant unidirectional flow e.g. batteries
159
AC
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)
160
voltage
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
161
SI unit voltage
Volt, V
162
potential difference
voltage
163
electron movement between shells
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
dental xray unit components
```
tubehead
collimator
positioning arm
control panel
circuitry
```
165
mains electricity supply
AC
| 220-240V
166
rectification of current
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
dental xray unit electricity requirements
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
transformers
alter the voltage (and current) from one circuit to another
169
2 separate transformers required for xray unit
mains to xray tube (cathode - anode)
| mains to filament
170
step-up transformer
increase potential difference across xray tube
usually 60-70kV
current reduced to mA
171
step-down transformer
reduce potential difference across filament
10V
10amps
172
xray beam intensity
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
a particles
stopped by paper
174
B particles
stopped by Al
175
y rays
reduced by thick lead
176
how are a, B, y different to X-rays?
all produced by radioactive decay of unstable atoms - unlike X-rays which are directly man-made
177
xray beam
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
divergence of xray beam
dose decreases with distance from xray source - beam diverges so not all xray photons irradiating them
179
inverse square law
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
when are X-rays produced?
when fast moving electrons are rapidly decelerated
181
xray tube head components
```
filament - cathode
transformer
target - anode
target surround
evacuated glass envelope (shielding)
filtration
collimator
spacer cone
```
182
filament - cathode
negative
tungsten
filament circuit (step-down transformer): low voltage, high current
183
tungsten
W
Z = 74
mp 3410 degrees - can reuse and it won't disintegrate/melt - it will retain its integrity
184
filament function
cathode
low voltage current passed through filament circuit
filament heats up to incandescence
e form a cloud around filament
185
operating potential
new equipment should operate within range 60-70kV
affects
- how X-rays will interact with matter
- pt dose
186
transformer - why hollow centre?
so X-rays can go through it so they don't interact with it
187
step-up transformer process
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
target - anode
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
target interactions
heat production 99% - inefficient
xray production <1%
- continuous spectrum (energy output)
- characteristic spectrum (characteristic to tungsten - material where interactions are happening)
190
target interactions - xray production: continuous spectrum
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
what is continuous spectrum also known as?
Bremstrahlung/braking/white radiation
192
target interactions: heat production
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
target surround
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
why are low energy X-rays not useful?
don't have enough energy to get through the tissues and produce an image
195
describe the appearance of the graph for continuous spectrum of xray energies
```
number of photons (intensity) - y axis
photon energy (KeV) - x axis
straight line decreasing (linear) to 70
```
196
characteristic spectrum of tungsten xray energies
characteristic radiation of tungsten has values of approx
- 8kV - L shell
- 58kV - K shell
- 68kV - K shell
197
filtration
get rid of low energy X-rays that you don't want
198
material used for filtration
Al Z = 13
- high energy X-rays will get through
1. 5mm ≤ 70kV
2. 5mm > 70kV
199
what does the spacer cone do?
control the target FSD
200
where is FSD measured between?
external marker and pt end of cone
201
FSD distances
100mm <60kV
| 200mm ≥ 60kV
202
target interactions - xray production - characteristic spectrum
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
glass envelope
evacuated glass
| vacuum prevents risk of interaction of electrons with air atoms prior to meeting target
204
shielding
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
collimator
lead
circular or rectangular diaphragm
max bean diameter 60mm at pt end of spacer cone
206
what does a long FSD reduce?
magnification
207
xray photons traversing tissue may:
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
production of a radiographic image
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
attenuation
reduction in number of photons (X-rays) within beam
occurs as a result of absorption and scatter
affects number of photons reaching IR
210
effect of photon absorption on image
all photons reach film - black
partial attenuation - grey
complete attenuation - white
211
principal interactions of diagnostic X-rays in tissue
photoelectric effect - absorption
| Compton effect - scatter and absorption
212
what does PE effect result in?
complete absorption of photon energy - photon does not reach film
213
PE effect
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
effect of PE absorption on image
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
occurrence of PE absorption proportional to:
atomic number cubed (Z³)
1/photon energy³ (1/kV³)
density of material
216
PE absorption - atomic numbers and cubes
relatively small differences in Z result in large differences in PE absorption
- good differentiation between tissues
217
Compton effect - first stage
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
Compton effect - what happens to excess energy in the original photon?
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
Compton effect - following scatter events
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
Compton effect - what happens to scattered photons?
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
probability of Compton effect occurring
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
effect of Compton scattered photons
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
reduction of scatter - methods
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
effect of PE absorption on dose
deposition of all photon energy within tissue - increases pt dose but necessary for image quality
225
effect of Compton scatter on dose
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
effect of high kVp on image quality and pt dose
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
absorption of photons more likely if:
object traversed has a high atomic number
object traversed is thicker
photon energy is lower
228
radiographic contrast
difference in density in light and dark areas of radiograph
| image showing both light and dark areas with clear borders - high contrast - ideal
229
when is contrast greatest?
when difference in absorption by adjacent tissues is greatest
230
effect of low kVp on image quality and pt dose
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
what is the chosen kVp a compromise between?
diagnostic quality of the image and dose
| 60-70kV
232
a particle
2p/2n
large particle, travels a few inches
most damaging type of radiation
233
B-particle
e-
| v small particle, travels a few feet
234
y-ray
EM
high energy
travels long distances
235
ionising radiation
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
interaction of radiation with tissues
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
single strand break in DNA
can usually be repaired
238
double strand DNA breaks
more difficult to repair
usually result of a radiation
if the repair is faulty - can lead to mutations which can affect cell fct
239
factors affecting the biological effect of DNA damage
type of radiation
amount of radiation (dose)
time over which the dose is received (dose rate)
tissue or cell type irradiated
240
what is the most significant effect of ionising radiation?
damage to DNA
241
evidence of DNA damage
can be seen in faulty repair of chromosome breaks
242
direct effect DNA damage
radiation interacts with atoms of a DNA molecule or another important part of the cell
243
indirect effect DNA damage
radiation interacts with water in the cell, producing free radicals which can cause damage
free radicals are unstable, highly reactive molecules
244
dose survival curves
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
dose rate
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
possible outcomes after radiation hits a cell nucleus
```
no change
DNA mutation
- mutation repaired - viable cell
- cell death - unviable cell
- cell survives but is mutated - cancer?
```
247
dose quantities - tissue cancer risk
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
what is tissue radio sensitivity dependent on?
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
SCs and tissue radiosensitivity
exist to produce cells for another cell pop - divide freq, v radiosensitive
250
differentiated cells and tissue radiosensitivity
do not exhibit mitotic behaviour, less sensitive to radiation damage
251
highly radiosensitive tissues
```
bone marrow
lymphoid tissue
GI
gonads
embryonic tissues
```
252
moderately radiosensitive tissues
skin
vascular endothelium
lungs
lens of eye
253
least radiosensitive tissues
CNS
bone and cartilage
CT
254
dose
measure of amount of energy that has been transferred and deposited in a medium
255
why have additional dose units been defined?
to quantify the level of biological damage and the overall effect of the dose
256
severity of ionising radiation
effect of ionising radiation on tissue is greater than would be expected from amount of energy involved
257
what might heavily damaged cells be programmed to do?
die
258
absorbed dose
measures the energy deposited by radiation
Gy
= but different types of radiation can cause different levels of damage to tissues
259
equivalent dose
absorbed dose multiplied by a weighting factor depending on the type of radiation
B, y and X-rays - 1
a particles - 20
Sv
260
equivalent dose units
Sv
261
absorbed dose units
Gy
262
what does the LNT model estimate?
the long term biological damage from radiation
263
LNT model assumptions
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
deterministic effects
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
stochastic effects
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
lethal dose
6Sv to whole body
267
subdivision of stochastic effects into 2 categories
somatic - disease/disorder e.g. cancer
| genetics - abnormalities in descendants
268
pregnant pts
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
effects of radiation during early pregnancy
```
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
sources of natural background radiation
```
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
estimated annual background radiation dose
2.2mSv
272
UK pop split of natural and artificial radiation
84% natural (50% of this radon gas)
| 16% artificial
273
IO xray effective dose
0.005mSv
lifetime risk of cancer 1 in 10m to 1 in 100m
negligible risk
274
protection of staff - dose limits to body
employee 20mSv
U18 trainee 6mSv
other 1mSv
275
protection of staff - controlled area
should extend at least 1.5m from the xray tube and pt
| xray beam should always be directed away from staff
276
dose optimisation
```
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
images with minor artefacts or non-uniformities should be saved
refer to these if suspected artefact in clinical image
| can also be used for training purposes
278
CBCT
sectional images
| thin slices, usually 0.4mm or thinner
279
DRLs
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
current DRLs for IO exams - adult
0. 9mGy digital
| 1. 2mGy PP and film
281
current DRLs for IO exams - child
0. 6mGy digital
| 0. 7mGy PP and film
282
what do digital and film radiography differ in?
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
size 0
ant PAs
284
size 2
BWs, post PAs
285
size 4
occlusals
286
receptors
```
digital
- PP
- SSS
film
- direct action film
- indirect action film
```
287
conversion of xray shadow into image
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
digital radiography - xray shadow to digital image
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
the digital image
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
number of pixels
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
greyscale bit depth
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
manipulating digital images
```
software can be used to copy, resize and alter images
contrast/windowing
negative
emboss
magnify
```
293
management of digital images: PACS
Picture Archiving and Communication System
storage and access to images
archives for storage and retrieval
294
viewing digital radiographs
```
env - subdued lighting, avoid glare
monitor
- clean
- adequate display resolution
- high enough brightness level
- suitable contrast level
```
295
format for digital images - DICOM
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
SMPTE test pattern
Society of Motion Picture and Television Engineers
| can be used to assess the resolution, contrast and brightness of your monitor
297
types of digital IO receptor
SSS e.g. CMOS sensor
| PP e.g. PSP plates
298
PP after taking xray
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
image creation using PPs - in mouth
receptor exposed to xray beam
| phosphor crystals in receptor excited by the xray energy - create a latent image
300
image creation using PPs - in scanner
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
types of SSS
CCD (charge-coupled device)
| CMOS (complimentary metal oxide semi-conductor)
302
SSS creation of image
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
SSS components
```
back housing and cable
electronic substrate
CMOS imaging chip
fibre-optic face plate
scintillator screen
front housing
```
304
SSS - CMOS imaging chip
light converted to electrical signals
305
SSS - scintillator screen
emits light when xrays hit
306
identification dot
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
cross-infection control
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
why should you hold receptor by edges not by flat surfaces?
scratches/tears
fingerprints
bending/creases
309
importance of careful handling
certain types of damage will impact every subsequent image obtained from that receptor
- reduce diagnostic value and may render receptor unusable
310
advantages of PPs
thinner and lighter
(usually) flexible - good if limited mouth opening - can bend a bit going into mouth
wireless - more stable and comfortable
311
disadvantages of PPs
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
SSS disadvantages
bulkier and rigid
usually wired
sealer active area (for same physical area of receptor)
£££
313
SSS advantages
no issues with room light control - light can't get through hard plastic
arguably more durable - replaced less often
314
components of radiographic film packet
protective black paper
lead foil
outer wrapper
film
315
components of radiographic film packet - protective black paper
protects film from light exposure, damage by fingers and saliva
316
components of radiographic film packet - lead foil
absorbs some excess xray photons - not contributing to image, will just enter pt and cause damage
317
components of radiographic film packet - outer wrapper
prevents ingress of saliva
| indicates which side of the packet is the front
318
components of radiographic film packet - film
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
radiographic film structure
transparent plastic base
adhesive
emulsion
protective coating of clear gelatin
320
radiographic film structure - transparent plastic base
supports the emulsion
321
radiographic film structure - adhesive
attaches the emulsion to the plastic base
322
radiographic film structure - emulsion
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
radiographic film structure - protective coating of clear gelatin
shields the emulsion from mechanical damage
324
film - silver halide crystals mechanism of action
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
film speed
relates to amount of xray exposure required to produce an adequate image
increased speed - reduced radiation required to achieve an image
326
what is film speed affected by?
number and size of silver halide crystals
| - larger crystals - faster film but poorer image quality
327
what film speed should be used?
the fastest film which still provides satisfactory images
328
comparing E and D film
E is twice as fast as D
- therefore requires half exposure time - half radiation dose
- most commonly used film
329
comparing E and F film
F is 20% faster than E
- 20% reduction in exposure time (and dose)
requires automated processing - not everyone has this in practice
330
if changing to a different film speed must either:
convert settings on xray unit (by a qualified technician)
| install a filter to absorb part of the primary xray beam
331
lead foil
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
what are intensifying screens used alongside?
special "indirect action" film for EO radiographs e.g. pan, ceph
- too bulky for IO use
333
effect of intensifying screens
reduce radiation dose
| but reduce detail - slightly fuzzier as it is being spread out by the cone of visible light
334
why are intensifying screens becoming less commonplace?
digital receptors more common
335
how intensifying screens work
"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
film processing
steps which convert the invisible latent image to a permanent visible image
need controlled, standardised conditions to ensure consistent image quality
337
methods of film processing
manual
automated
(self-developing)
338
film processing common steps
```
1 - developing
2 - washing
3 - fixing
4 - washing
5 - drying
```
339
film processing step 1
developing
| converts sensitised crystals to black silver particles
340
film processing step 2
washing
| removes residual developer solution
341
film processing step 3
fixing
removes non-sensitised crystals
hardens emulsion (which contains the black silver)
342
film processing step 4
washing
| removes residual fixer solution
343
film processing step 5
drying
| removes water so that film is ready to be handled/stored
344
manual (wet cycle) - what happens?
person dips film into different tanks of chemicals
- at precise concs/temps
- for specific times
- washes film after each tank
345
manual (wet) cycle requirements
dark room with absolute light-tightness
| adequate ventilation
346
how long does manual (wet) cycle take?
about 20mins
347
difference in steps between manual and automated cycle
extra washing step in manual
| in automated - sponge rollers squeeze developer solution out of film (instead of washing with water)
348
automated cycle
```
machine
exposed film goes in at one end = processed film comes out the other
developer
fixer
wash
dryer
```
349
pros and cons of automated cycle
faster (5mins)
more standardised/controlled than manual
avoids need for dark room
more £££
350
opening a film packet for automated processing
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
self-developing films
not recommended
| give tube a squeeze and the chemicals go up to where the film is
352
self-developing films pros
no darkroom or processing facilities required
| faster e.g. 1min
353
self-developing films cons
```
poorer image quality
image deteriorates more rapidly over time
no lead foil
easily bent
difficult to use in positioning holders
relatively £
```
354
potential causes of pale image
```
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
processing issues - washing
developer and fixer solution will continue to act if not washed away/off
- fixer - looks like bubbles
- developer - black spots
356
film storage
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
processing issues - developing
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
processing issues - fixing
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
advantages of digital
```
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
disadvantages of digital
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
caries diagnosis methods
```
visual - smooth and occlusal
radiography
elective temporary tooth separation
FOTI
electrical methods
laser fluorescence
calcivis - detects Ca2+ loss from demineralising tooth surfaces
```
362
caries clinically vs on radiograph
always larger clinically than on radiograph
363
cervical burnout
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
PD assessment - selection criteria recommendations
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
which wall of MS don't you see on a pan?
lat wall (see post wall)
366
PD radiography techniques
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
EO radiography definition
xray source and IR outside pt
368
lateral radiography types
true
| oblique
369
true lateral radiography
film and MSP are parallel and xray beam is perpendicular to both
370
oblique lateral radiography
film and MSP are not parallel
| xray beam is not perpendicular to either, but oblique to both
371
OM line
RBL
| outer canthus of eye to centre of EAM
372
Frankfort plane
superior border EAM to lowest point of IO rim
373
difference between RBL and FP
10 degrees
374
cephalometric radiography
standardised and reproducible form of skull/facial bones radiography
used in ortho
lateral or PA projections
375
indications for lat ceph
```
orthognathic surgery
- pre-op assessment and post-op review
implant planning - historically
- anterior mandible - CS image
- now often CBCT
```
376
lat ceph distances
source to pts MSP = 152.4cm (5ft) in traditional equipment
| image receptor to MSP: manufacturer dependent, fixed or adjustable
377
effect of anode-object distance on magnification
longer - less difference in magnification as less divergent xray beam
378
lateral views
lat ceph
lat oblique (mandible)(OJ)
- only shows you one side of pt
bimolar - both sides on one receptor
379
lat ceph
true lateral view of facial bones, base of skull and upper cervical spine
also shows paranasal sinuses and nasopharyngeal STs
380
ortho radiographs - lat ceph
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
set up of lat ceph equipment
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
lat ceph collimation
height and depth of field of view or triangular - adjustable, by programme or visual
383
positioning and preparation for lat ceph
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
why can successive lat ceps be used to analyse changes?
fixed distances so subsequent images will always be able to be directly comparable
385
oblique lateral
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
indications for lateral oblique
generally same as for pan but particularly when pan not available or possible e.g. handicapped pt
no longer done at GDH
387
subjective quality rating - excellent
no errors of pt prep, exposure, positioning or film handling
| target >70%
388
subjective quality rating - diagnostically acceptable
some errors
does not detract from diagnostic utility
target <20%
389
subjective quality rating - unacceptable
errors make film diagnostically unacceptable
needs retaken
target <10%
390
reject analysis
unacceptable radiographs and reasons why?
| may be multiple errors - don't stop looking when you find one
391
what must PA contain?
must contain full length of roots
ideally full crown - but not critical as can examine it clinically
bone around the roots
392
what must BWs contain?
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
QA - prev dental guidance notes definition
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
QA - stages involved
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
coning off
incorrect film holder assembly or collimator orientation
396
density variation
exposure factors
object factors
processing factors
viewing facilities
397
monitoring processing
process test film daily
| compare with reference film
398
reference film options
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
darkroom and daylight loading processors
```
cleanliness
stock control - organisation
light tightness - room and cassettes
safelights - coin test
replenishment
```
400
quality of original - viewing conditions
dim room
transmitted light restricted to film
film sensitive to xrays and pressure
401
image viewing influenced by:
quality of original
equipment
env
knowledge base
402
dark crescents
nail pressure
403
safelight testing
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
elongated teeth - occ and PAs
error is decreased vertical angulation - how the beam is related to the occ plane
405
shortened teeth - occ and PAs
error is increased vertical angulation
406
pale IO image
too long fsd or inadequate development (development creates the dark bits)
407
IRR99 - 5 advised safety features
```
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
```
