Radiography and Imaging Flashcards
1
Q
What are the two audit qualities of radiographs and what percentage of each is acceptable
A
Diagnostically acceptable = 95%
Diagnostically = 5%
2
Q
What is the focal trough
A
The zone of sharpness that the patient must be placed in (guided by lines of light) to ensure a sharp radiograph
3
Q
How can you tell if a radiograph was taken outside of the focal trough?
A
Long, narrow and sharp incisors AND blurry/out of focus
4
Q
When taking a radiograph what should the patient do with their chest and tongue? And why
A
Press chest forward to minimize the image of the cervical spine and ‘suck on mouth peice’ so tongue goes to the palate to eliminate air over the dorsum of the tongue which would cause radiolucency over upper anterior roots.
5
Q
When taking a radiograph what should the patient do with their chest and tongue? And why
A
Press chest forward to minimize the image of the cervical spine and ‘suck on mouth peice’ so tongue goes to the palate to eliminate air over the dorsum of the tongue which would cause radiolucency over upper anterior roots.
6
Q
What colour is the radiograph request form and what does it need on it
A
yellow date signature sticker details of exactly which radiograph justification for each radiograph
7
Q
What do we write on a radiograph request if we want the patient to leave straight after taking radiographs?
A
patient can go
8
Q
if a patient has toothache but there is no obvious caries, what do we do?
A
Special tests
Bitewing of the symptomatic side or periapical for apical pathology
9
Q
When do we take periapical?
A
if we suspect periapical pathology or when the patient wants to save a tooth by RCT and the symptomatic tooth has been identified
10
Q
How often should caries detection bitewings be taken?
A
High caries risk - 6 months
moderate caries risk - 12 months
low risk - 24 months
11
Q
when would we take all round periapical or OPT? which would be best?
A
if the patient scored 3 s and 4s on BPE for periodontitis detection. All round periapical expose patient to more radiation than an OPT so the patient should get an OPT.
12
Q
Why do we take radiographs of bone with BPE of 3 or 4?
A
to stage and grade periodontitis for monitoring and diagnosis
13
Q
what are the 4 radiographs we take during RCT?
A
All periapical
- EWL radiograph before any treatment and for diagnosis
- AWL with master K file to test working length
- Master GP to ensure apical 1/3 is fully filled
- final fill
14
Q
Are adults or children more susceptible to radiation, by how much and why?
A
children are more susceptible by 3x than adults because they are growing and have much more dividing cells that have the potential to become cancerous.
15
Q
when do we take radiographs on children? (3)
A
- when a child needs teeth extracting
- determine presence of unerupted teeth
- in orthodontic planning for treatment is being done
16
Q
when should we not do an OPT on a child requiring orthodontic treatment?
A
if all teeth 7-7 are present
17
Q
For adults, when do we take radiographs for extraction and why is it rarely done?
A
for impacted 3rd molars as they have unexpected morphology and can have implications with the mandibular canal, nerves and maxillary air sinus. We don’t do them for anything else as even if we found something unexpected e.g. ankylosis, the tooth would fracture anyway and we cannot avoid it so the radiograph has no use.
18
Q
Which radiograph do we use for 3rd molar extraction? is it the same if we are only removing 1 tooth?
A
we use sectional panoramic x-rays for molars on 1 side to view the mandible but if there are molars on the e contralateral side that also need removing, a full panoramic radiograph
19
Q
what should we be able to see in a well taken bitewing
A
the crowns and coronal 1/3 of the root of upper and lower molars/premolars
20
Q
what should be seen in a well taken periapical?
A
the full crown and root of the tooth in question and at least the two adjacent teeth with at least 3mm of alveolar bone apical to the apex. Only upper OR lower teeth.
21
Q
What should a well taken OPT show?
A
all of the teeth, mandible, surrounding hard and soft structure
22
Q
How many bitewings do we need to take to equal the dose of radiation we get from background radiation in 1 day?
A
2 bitewings
23
Q
How do we ensure we are not providing unnecessary radiographs? what checks do we make?
A
- ensure the problem is not diagnosable without radiographs
- ensure a radiograph will improve prognosis
- ensure no recent radiographs can help
- do every other test first e.g. special tests
- follow guidelines
- regular audit quality checks
24
Q
what should be included on a radiograph report?
A
Type of radiograph
Site of radiograph (left/right/posterior/anterior/UL/UR)
Teeth present
Audit quality 1,2 or 3.
Coronal or radicular radiopacities
Coronal radiolucencies (caries/fractures)
Periapical radiolucencies (periapical)
Bone level. For bitewings; judgment of bone loss. For periapicals; estimation of percent of alveolar supporting bone remaining.
Any abnormalities like calculus (white granules on surface of teeth)
25
what are the audit quality criteria and what percent can be achieved?
for digital:
- 95% diagnostically acceptable
- 5% diagnostically unacceptable
for film:
- 90% diagnostically acceptable
- 10% diagnostically unacceptable
26
what is the FGDP
faculty of general dental practicioners
27
what type of intra-oral radiographs can we take
periapicals
bitewings
maxillary occlusal
mandibular occlusal
28
when do we not use a parallel technique for periapical and what do we use instead
we use a bisecting technique if a parallel access is not possible if we cannot place an image receptor holder in the mouth or due to abnormal anatomy
29
what is the parralellling technique for periapicals
- wall mounted xray beam
- image receptor holder placed in mouth parallel to the long axis of tooth
- x-ray beam perpendicular to long axis of tooth
30
what is the bisecting angle periapical technique?
- wall mounted x-ray beam
- no image receptor holder in mouth so film/receptor rests on palate and somewhere in mouth
- the angle that the image receptor makes with the long axis of the tooth is bisected
- x-ray beam is perpendicular to this bisecting line
31
why are radiographs slightly (3%) larger than real images?
the x-rays diverge when they leave the beam so spread out and create a larger image
32
when would a periapical be forshortened or elongated?
during bisecting technique
- if the angle between the top of the bisecting line is LESS than 90 degrees then image foreshortened
- if the angle between the top of the bisecting line is MORE than 90 degrees then image elongated
33
advantages and disadvantages of parallel technique for periapicals
adv:
- little elongation and foreshortening
- accurate and reproducible
- little superimposition of other structures
disadv:
- uncomfortable, often gives gag reflex
- holders need to be sterilized or thrown away
- sometimes not possible to fit holder in or painful
34
advantages and disadvantages of bisecting technique for periapicals
Adv:
- less sterilization needed as no holder
- more comfortable as no holder in mouth
Disadvan:
- more likely to get elongation/foreshortening
- not reproducable
- bone levels not clearly shown
- zygomatic butress superimposition during maxillary molar radiographs
35
why are bisecting techniques more likely to cause foreshortening/elongation of images?
we have to guess the bisecting angle of the long axis of tooth and the receptor and receptor is not held by anything stable, just patients oral structures
36
how do we set up a bitewing radiograph receptor and holder
- holder bite platform between teeth to get equal maxillary and mandibular imaging
- receptor in sulcus with mesial and distal ends equidistant from lingual aspects of teeth getting it as parallel as possible to teeth
37
what radiographic pre-assessment do we take before PD treatment?
level of periodontal bone support;
the full extent of any associated bone pathosis – i.e. the entire border of any lateral or periapical radiolucencies must be visible;
the location and proximity of any relevant anatomical structures such as maxillary antrum, mandibular nerve etc.;
number of roots, their morphology and location; curvature
size, position and patency of the pulp chamber;
patency of and root canals with evidence of any obstructions;
the presence of any existing root canal filling and the quality thereof.
38
with a trauma patient, what images would you take
take a few at 90 degrees to each other to check all dimensions for fractures.
May also include MRI or Ct to check brain and soft tissues
39
if someone has TMJ pain and it is not going away, what scans do we do? why?
open mouth panoramic to detect normal bony structures and rule out aggressive tumour that would also be palpable. This is good for detecting hard tissues e.g. bone
MRI to check the position of the disc as good contrast and high resolution with soft tissues
40
if you were trying to see a tooth or bone fragmented in soft tissue, what would you do to the xray?
reduce its exposure
41
when viewing a radiograph, how can you make sure that your view is not impaired and that you make proper diagnosis?
-shut blinds and remove sunlight. want twilight setting
-know the natural anatomy to be able to find abnormalities
-understand 3D objects will be 2D
-developed a system to check everything. Don't miss anything
-
42
why is it important that we don't miss anyting on a radiograph?
-if we miss a major artefact e.g. tumour that leads to worsened prognosis e.g. longer in hospital/death, fractures or failed treatment this is negligence and can lead to medico-legal issues.
43
what is the IRR2017 act
ionising radiation regulations 2017 act is a document about the protection of the operator from a radiation machine
44
what is a referrer, practitioner, employer and operator
All registered healthcare professionals and all should comply with employers procedures
referrer can refer someone to a practitioner to have a radiograph taken
practitioner takes responsibility for individual exposure e.g. is it justified?
operator can apply a radiation dose
employer is responsible for IRR2017 exposure to all employees, keeps records of all radiography equipment and training history
dentist can be all 3
45
What is IRMER 2017
Ionising radiation medical exposure regulations 2017
| legislation accounting for the saftey of all patients undergoing ionising radiation
46
what is involved with an IRR2017 risk assessment
identify hazards with potential of radiation accident
evaluate nature and magnitude of risks
record risks
identify provisions - information, training and equipment needed
review and revise frequently
must be written down
47
when do we do an IRR2017 risk assessment
When any new procedure, equipment or location is introduced
48
What is ALARP
```
As
Low
As
Reasonably
Practicable
Provide the least exposure possible that is still clinically relevant
```
49
How can we enforce ALARP
Hierarchy of controls
- engineering controls e.g. doors, walls, switches
- administrative controls e.g. signs, rules, lights
- PPE e.g. lead aprons, radiation badge
50
What is a radiation badge and what do we do if its limit is exceeded
a badge that an operator wears and it records the exposure gained from radiation of procedures.
If their Sv limit is exceeded a report should be sent to HSE - health and saftey executive
51
When should we contact the HSE
health and safety executive - registering a practice for ionising radiation
if an operators exposure is higher than the standard amount
52
what is the maximum annual dose for workers and public on the skin (1cm^2) or extremities
500mSv for workers
| 150mSv for general public
53
what is the annual maxiumum dose of radiaiton to the whole body for workers and public
20mSv for workers
| 1mSv for public
54
what is the annual maximum dose of radiation for public and workers for the eyes
20mSv for workers
| 15mSv for public
55
when does a radiation danger sign need to be on a room
when the room experiences over 6mSv annually
56
when is a radiograph justifiable
| when should we be more careful taking radiographs
when the benefits outweigh the risk and provide clinical relevance
Be more careful if a woman is pregnant or breastfeeding
57
What is the risk of doing an OPT
expose salivary glands and brainstem to radiation
| radiation scatter to other radiosensitive organs like thyroid and cornea
58
what makes an organ radiosensative
IF it is prone to cancer due to high cell turnover rate e.g. glands
59
what does a radiograph justification include
factors related to pt dose e.g. cancer risk, pregnancy, breastfeeding
reason for referral, does it outweigh the risk?
60
What is optimisation of radiograph taking?
ALARP as low as reasonably practicable
use the right equipment and procedure and radiograph type
assess patient dose
DRLs
61
What are DRLs and expand
diagnostic reference levels
determined by the employer
help determine if an exposure if abnormally high/low for set procedure
62
How do we set DRLs
in units that help calculate patient dose e.g. exposure time, current etc.
63
When might we have a radiation exposure incident and who do we report it do
```
accidental exposure
equipment fault
wrong exposure
wrong xray type
wrong patient
Report to CQC care quality comission
AND HSE health safety executive
```
64
Who are the CQC
care quality commission responsible for enforcing IRMER
65
What is a photon
a packet of energy released from electrons when moving down an energy level
can be thought of as a single particle of xray
66
what is an xray beam
An emission of lots of photons targeted to an area
67
what is the energy and name of the first and second shell and why is this significant
E=10 on K shell and E=30 on L shell
electrons on these shells have exactly E=10 or E=30
if they do not, they must release/take in energy to join one of the shells
68
what is ionisation
when we give an electron enough energy to free it from the electromagnetic pull of the nucleus leaving a positive ion and a free electron
69
explain alpha radiation
type of particulate radiation
an unstable radiative nucleus emits 2 protons and 2 neutrons to reduce the atomic number by 2
a helium nucleus is released with very high ionising power due to size and enegry
70
what would stop the travel of alpha radiation
10mm of air or les than 1mm of matter
71
What is beta radiation and what is a beta particle
type of particulate radiation
beta particle is an electron
Unstable radioactive nucleus converts a neutron to a proton and electron
very ionising
72
what would stop a beta particle and how penetrating is it compared to alpha radiation
more penetrating than alpha radiation
| a few mm of aluminium
73
what is electromagnetic radiation
beams of photons, not charged, released from atoms
travel at speed of light
ionising power relates to energy of photons
74
what is particulate radiation
radioactive small particles (alpha or beta) released by radioactive decay of unstable atoms
speed is determined by the energy of particles, not necessarily speed of light
75
breifly explain the electromagnetic spectrum
```
radiowaves
microwaves
infared
ultraviolet
soft xrays
hard xrays
gamma rays
increasing eneegy of photon
increasing frequency
decreasing wavelength
```
76
what is gamma radiation
type of electromagnetic radiation
released from excited nuclei going back to resting state
released from beta and alpha particulate radiation
less ionising than particulate radiation
very penetrating e.g. Pb
77
Explain the production of an xray beam
within a vaccum
current pases through a filaemtn, causing it to give up electrons
a high voltage is set up between anode and cathode
electrons are drawn to the anode and accelerate toward tungsten target
Braking and characteristic radiation takes place
photons are released at energy of xrays (100KeV to 100eV - WL 0.01nm to 10nm)
Focusing device (Lead sheet) directs the photons to specific area
78
what is the range of wavelengths and energys of xrays
100KeV to 100eV
| 0.01nm to 10nm
79
How much energy is lost as heat in xray production
99%
80
why is tungsten used in x-ray beam (2)
very high atomic number - more efficient x-ray production
| very high melting point - doesn't melt under high heats produced
81
what is the typical voltage between anode and cathode in xray tube
60kVp (maximum energy of photons produced is 60kVe)
82
what is the glass envelope for (during xray production)
keeping the vaccum sealed
83
what is the copper block for in xray production
```
transferring heat from the target
filtering out low energy photons
reduces intensity and exposure
increases mean energy oh photons
increases contrast
```
84
what is breaking radiation
where there is a rapid deceleration (changing direction) of electrons passing close to a target nucleus
Very likely to get lots of low energy photos rather than few of the high energy
85
What is characteristic radiation
where an electron is knocked off of the K shell and hits the electron off. To replace this, an electron moves down from the L shell and emits a photon x-ray.
86
how do we find the energy of a photon from characteristic radiation
energy of shell that the electron comes from e.g. E=30
minus
energy of the shelll that the electron moves down to e.g. E=10
30-10 = E20
87
what is the energy equation used for radiation
```
E = hv
E= energy
v= wavelength
h = Planck constant
```
88
what are the differences between ionising radiation and particulate radiation
ionising radiation has a spectrum of energies, no particles released (no mass), speed of light
particulate radiation released particles with set energies, not speed of light
89
why cant we use alpha or beta radiaiton for scans
too ionising
| wont make it through to other side of tissue therefore won't help detect structures
90
what happens if we increase voltage of xray tube
higher energy, shift up the spectrum
| more penetrating to get through harder structures e.g. skull in OPT
91
What happens if we use a metal with higher atomic number in xray tube
more photons released
92
what is attenuation
ratio of energy photons going into a tissue related to the photons coming out the other side
93
what is the half value layer value?
the thickness of a material in which the number of photons halves when a beam passes through it
94
What is beam hardening why should we not over do it
take advantage if attenuation
Pass photons through a thin layer of material to absorb any low energy photons to increase average photon energy of beam
If we do this too much, only very high energy photons will get through which will all pass through body tissue so will just give a black image
95
what is the inverse square law in relation to xrays
when we move x meters away from the source of xrays
amount of photons that hit us reduced by x squared
due to dispersion of xrays travelling in all directions and being absorbed by the air
96
what is the photo electric effect
where a photon hits the atom of a patients tissue causing ionisation and another much lower energy photon to be released and absorbed (due to difference in atomic number to tungsten)
gives good contrast between high and low atomic mass of atoms within patient tissue
97
when does photoelectric effect occur and what are its positives and negatives
10-100KeV - low energy beam
+ high contrast
- worse picture as not many photons make it through at low energy and underexposed
98
what is the compton scatter effect, when dose it occur and what is its relevence
a photon of high energy ionises and scatters off of many atoms
occurs at higher energies near 1000KeV
scatters image therefor makes blurry
99
what is the only factor/control of xray beam that alters energy of xray beam
KvP kilovoltage peak
100
what KvP = 100keV
100KvP
101
what are KeV
kiloelectro volts - measurement of energy of photons
102
with increased KvP we get...
increased dose (more photons)
increased penetration therefore
increased exposure (15% increase KvP = 2x exposure)
increased energy and speed
decreased contrast (less photoelectric effect)
103
what are the 4 prime exposure factors
KvP tube voltage
tube current
exposure time
distance from tube
104
an image is darker but with the same level of contrast. what has changed and what has caused this change
intensity
| number of electrons and photons caused by KvP
105
an image is lighter but also has higher contrast, what has caused this?
increased quality of electrons
higher energy photons
lower KvP
106
what is contrast in radiograph
how many grey levels are shown on the image
107
what does the exposure time of a radiograph change and how easy is it to change
easiest factor to change
| alters intensity of image
108
if exposure time is too high or low what happens to the radiographic mage
too high = dark image, overexposed
| too low = light image, underexposed, noisy
109
what happens if we change the current of the filament in the xray beam and how easy is it to change
usually cannot change current
doesn't increase energy just the intensity
too high = too dark, overexposed
too low = too light, underexposed
110
what is the density of an image
darkness
111
what happens when we change KvP of an xray beam
changes intensity and energy of beam
too high = low contrast, darker, comptom scattering
too low = high contrast, lighter, more photoelectric absorption
112
what is collimation and what effects and what is its maximum diameter
directing of the photon beam by a lead covering
reduces unnecessary patient exposure
reduces scattering noise therefor increases image quality
no more than 6cm diameter
113
how far should the operator stand form the source of radiation
at least 6 ft
114
what three distances are important in radiology
source to object SOD
source to image SID
object to image OID
115
what affects does SOD and SID have on the image (think of a flashlight and pencil)
any increase in distance decreases intensity
increased SOD, increased sharpness
decreased SID, increased sharpness and decreased magnification
116
what ideal distances do we consider when taking a radiograph
highest possible SOD and lowest possible SID within reason
| balance overall OID with intensity and dose
117
what is umbra and penumbra
umbra is the centre shadow where no light reaches
| penumbra is the side shadow where it is blurry - some light reaches, some does not
118
how do we reduce penumbra and why do we want to reduce it
recues side shadowing and increases contrast and resolution, reduced blurriness
decrease the focal spot size (size of beam)
decrease OID
increase SOD
119
what two factors alter contrast of any radiographic image
increased tube voltage KvP decreases contrast
| increased filtration increases contrast
120
what is a Gray
absorbed dose of radiation
121
How do we get from Greys to Sieverts
absorbed dose (Gy) x suseptability weighting factor
122
what is annual background radiaiton
2.7mSv from CMBR
123
what are siverts
unit of radiation weighted for the harmfullness to particular tissues
124
if we apply 2 grays to one part of the body and 2 grays to a different part of the body, will they experience the same Sv
not necessarily
| depends on their susceptibility to ionising radiation and their weighted factor
125
how does radiation effect DNA (2)
hit the DNA directly ionising atoms
| ionise water forming free radicals that attack DNA
126
what's the difference between somatic and genetic radiation effects
```
somatic = accumulation of radiation dose form a persons life
genetic = problems arising in the offspring of someone who experienced radiation dose
```
127
what are deterministic effects involving radiation
direct consequences of doses higher than the threshold for that particular tissue
increased radiation dose increases the severity of effect (when above threshold)
e.g. burn on skin
128
what are stochastic effects involving radiation
increase in likelihood but not severity with increasing dose
no minimum threshold
e.g. risk of cancer increases as we increase dose but severity of the cancer remains the same
129
what is the difference between effective dose and dose equivalent
dose equivalence is the amount of radiation to 1 organ weighted by the type of radiation and sensitivity of that organ to radiation
Effective dose is calculated for the whole body, summing the dose equivelence
130
what is the sum of all weighting factors of the organs in the body
1
131
which parts of the body hold highest weighting factor
bone marrow, breats, stomach, lung
132
how do we get from greys to dose equivelence (mSv)
weighting factor x Gry
133
how do we get from Gry to effective dose?
Gy x 1 (as weighting factor of whole body is 1)
134
where dose most radiation come from
radon gas, food, sun and CMBR
135
what is the effective dose (whole body) required for chromosomal changes, radiation sickness, possible death and certain death?
chromosomal changes: 0.1Sv
radiaiton sickness = >1Sv
Possible Death= >3Sv
Definite Death= >10Sv
136
what is the absorbed dose locally needed to form erythema and desquamation
```
erythema = >5
desquamation = >20
```
137
how much background radiation do we experience in 1 day, what assumptions have you made
10 microseiverts or 0.01mSv
| assuming no flight, average radon exposure
138
how much radiation are we exposed to in an intra-oral radiograph and related to daily background radiation. What do we say if a patient is worried?
0.3-21.6 microseiverts
average the same as 1 days worth of background radiation
very little risk
obviously there is risk but there is 1 in 1000,000 chance of it causing cancer. higher chance of winning lottery.
139
even though there is a tiny chance of radiation causing cancer from intra-oral exams and OPTs why must we only take them IF they are needed?
even though very small risk, 20Million oral radiographs and 3Milion OPTs are taken a year so there is still significant cancers caused by these radiographs
140
how much radiaiton are we exposed to during an OPT
2.7 -38mSv
141
where to we wear dose badges and for how long
between shoulder and waist NOT LANYARD
| for 3 months a year
142
what are the whole body limits of radiaiton in 1 year for staff?
20mSv
143
what is the heirarchy of controls
a way of preventing radiation incidents
- engineering: shielding within x-ray tube, walls, doors, locks
- Administrative: controlled areas, signs, lights, rules
- PPE : lead aprons
144
what is the CE marking
marking stating that the product adheres to european health, safety, and environmental protection standards and can be sold in the EU
145
what is a radiation protection advisor and when are they needed
can advise employers on safe and compliant use of radiation
| needed when setting up a practice to help shielding advise for the rooms in which radiation machines will be
146
what is a radiation protection supervisor
appointed by the employer to oversee radiation work and make sure local rules are followed.
147
what is a medical physics expert
Role under IRMER to assist with optimisation – set exposure parameters/RDLs to give best images for lowest dose
May be same person as RPA, but separate responsibilities
148
what does radiation shielding involve and who advises this
```
thick walls
material the wall is made out of
how much lead in the door
shielding in the xray tube
Radiation protection advisor
```
149
how can shielding be implemented into existing buildings
Lead or barium panels implemented into the walls
150
when do we take an OPT
When a lesion/unerupted tooth is of such a size or position that it cannot be demonstrated fully with intra-oral films
Pathology in all 4 quadrants of the jaws
For periodontal disease when pockets > 6mm in all quadrants
Assessment of third molars prior to surgical removal
As part of an orthodontic assessment in the mixed dentition
Following trauma
For implant planning
Open panoramic if a TMJ symptomatic click
151
describe the structure of x-ray film
translucent blue plastic base for integrity and structure of film
either side of this; adhesive coating to protect
the emulsion containing silver halide
covered by protective layer made of gelatin to help chemistry of film
152
what is the protective layer of a film made of
gelatin
153
why is there emulsion both sides of an x-ray film
to have more blackening for the same dose therefor requiring less dose
154
describe the structure of an x-ray film screen
x-ray film in the middle
either side a transparent protective sheet
phosphor layer that converts x-ray to light which amplifies the energy
reflective layer to reflect rays back to the phosphor/film
plastic base outer
155
how does an x-ray film screen reduce dosage given to patient (3)
x-ray film has emulsion either side of base to increase blackening for a set dose
phosphor layer converts x-rays to light. X-rays have more energy so the energy amplifies
reflective layer outside the phosphor reflects x-rays back to the x-ray film
156
why does a phosphor layer reduce resolution
x-rays are converted to light rays which have less energy so they amplify and converge so spread out from interaction point increasing the area of blackening
157
what is 'speed' in terms of x-ray film
the amount of film blackening for a given x-ray dose. For a fixed dose, the blacker the screen the faster the speed. The faster the speed, the lower dose needed for an image.
158
if we had larger crystal size in film xrays what would this affect
more blackening, worse resolution
159
how does an xray emulsion work
silver halide ions in emulsion
photons hit the halide ions and provide enough energy for another photon to be released and form a negatively charged crystal
crystal activation
this crystal attracts positive silver ions from the crystal to form silver atoms
crystal acts as a trap for other ions
forms small deposits of silver
this image is still invisible
160
what is a developing solution used for within dental xrays
reducing agent
converts remaining silver ions to silver atoms
begins at already formed crystals to enhance the sensitivity specs
cant leave for too long or whole film will become blackened
161
what is a developing solution used for within dental xrays
reducing agent
converts remaining silver ions to silver atoms
begins at already formed crystals to enhance the sensitivity specs
cant leave for too long or whole film will become blackened
162
what is the fixer solution in xrays and what needs to be removed before its use
acidic solution that removes any unreacted silver halide ions
remove developing solution as they will react
163
what 4 washes do we do after x-ray exposure to a film
developing solution (reducing agent to react with silver halide crystals)
wash to remove excess developing solution
fixer solution (acidic to remove any unreacted silver halide crystals)
final wash to remove fixer solution as this will react with light and form brown marks
164
compare digital and film radiography
digital:
- less time
- less radiation
- no chemicals
- image enhancement
- less cost
- less waste (fixer, developing solutions)
- less space (no dark room)
film:
-better image quality - contrast
165
why is silver halide used
sensative to x-ray photons and visible light photons
166
which xray film would need more exposure: speed B or speed D
speed B as speed increases from A-F
| faster speed, less exposure time
167
what affects speed of xray film
whether film is double emulsion
larger crystals (come with less resolution)
radiosensitive dyes added to emulsion
phosphor layer
168
what is a latent xray film
invisible film with reacted crystals that needs to be developed to form an image
169
what converts a latent image to a visible image
devloping solution (reducing agent) reduces crystals to silver atoms forming grey metallic specs
170
what speed film is used in dentistry
400 speed
171
what is fog and when do we get it on dental films
fog is background radiation ionising some of the phosphor on film screens causing very slight 'fogginess'
we get it with aged films
172
why must we not use an old film for xrays
fog will be high and may give false readings/diagnosis
173
what does fog alter
contrast as it alters the ratio between blackened and non-blackened crystals
174
why do we get magnification of x-rays
x-rays have a point source and disperse/diverge
pass through objects and diverge more before hitting the receptor
image larger than object
175
why do we have a point source in xrays
smaller point source have higher resolution and less image spreading
176
at what exposure do we get movement blurriness
1/10 seconds
177
how do we reduce fogging
keep the film cold and use new films
178
if a film is brown what has happened
not enough film washing and daylight has been absorbed
179
if a xray is very pale, what has gone wrong
not developed enough
180
if an xray is too dark, what has happened (digital and film)
overexposed
| over-devloped
181
what are some causes of unsharpness
geometric: object too far from film
motion: exposure over 1/10
absorption: not having sharp edges on teeth
resolution: crystal size
182
why is digital processing better than film processing radiography
improved dynamic range allowing us to alter contrast, exposure on computer
digital processing is much faster than devloping, fixing, washing
Digital storage, retrieval & transport (PACS) so we don't lose the image allows cooperation with other dentists
computer aided detection
183
why is film radiography better than digital
continuous spectrum of grey scale
digital has a discrete grey scale
therefor film has better contrast
184
what happens after image is captured with digital radiography
information is transformed into binary code (0s and 1s)
185
what are the two types of digital sensor used in digital xrays
CMOS/CCD - charged comp device
| CR - computed radiography
186
explain CR digital xray receptors
photons pass through patient at different energies
hit the phosphor layer (commonly PSP photostimuable phosphor)
phosphor stores energy of photons
laser stimulation released photons in form of visible light (blue)
light passes through photomultiplier tubes to measure intensity
intensity of light is directly related to intensity of photons
This information is relayed to the CPU and stored
187
what is PSP
Photostimuable Phosphor
barium flour halide doped with europium
used in Computer Radiography CR to capture and store energy of x-ray photons
188
what is CCD/CMOS
digital radiography
silicon sensor chip to capture x-rays with light emitting phosphor
rapidly converts to electric charge proportional to flash of photons
charge pattern forms image on CPU
189
what limitations do we have of CMOS/CCD
can only be made to size of 5cm^2 so limited to small, intra-oral radiographs
quite thick lading to gagging and discomfort
190
what is a line pair and how is it related to resolution
a line pair is 1 pair of dark (radiolucent) and light (radio-opaque) line
how many line pairs that fit into 1mm of image gives us resolution
lp/mm
191
how is resolution of digital images measured
in lp/mm
| how many line pairs are found within 1mm of image
192
what is the price relativeness of film, CCD/CMOS and CR
film < CR < CCD/CMOS
193
what is a digital image usually divided into
512 x 512 pixels
194
how is information stored in a digital pixel
stored in binary relating to its intensity - series of 0s and 1s
195
what controls the number of grey levels in a digital image? expand.
bit depth
if bit depth was 1 then there would be 1 or 0 (white or black - 2 options)
if bit depth was 2 then there would 11,01,10,00 (4 options)
if bit depth was 3 then there would be 111,110,101,011.... (8 options)
2 to the power of bit depth
e.g. bit depth of 13 would be 2^13 options
196
what bit depth do we usually have and therefor how many options for colour do we have
bit depth 12
| 4096 grey scale options
197
why are all bit values not used in images? how many are used? why?
we usually have 12 bit image with 4096 options
this would lead to very poor contrast between images
256 grey scale values are displayed over a set pixel range (window)
centred around a level
198
what is a window and level in digital radiographic images
window is a set range of pixel values that the 256 greyscale is spread over
centred on a set level
199
what do we get if we alter the window of an image
grey scale is spread over more of the 4096 pixel levels
| therefore less contrast if window increased
200
what do we get if we increase the level of an image
if we lower the level, we lower the midpoint of the pixel window
therefor see lower level pixels
therefor lower level photons
therefor more visible soft tissues/less dense
201
if there is a small radio-opaque perfect circle on a digital radiograph, what has gone wrong
The receptor has a zinc circle on the back
it has been taken back to front
will also be the wrong side of the face
202
how can we tell if a digital laser has malfunctioned
if there are straight, irregular lines going down the image
203
if we get a rigid radioaque line on the short edge of the image, what has happened
PSP delamination, started to come off of the receptor after repeated use
204
if there are straight, slightly white lines crossing the image, what has happened to the image receptor
PSP has bent
205
if there is a thin, regular radiolucency running under a radio-opaque restoration, what is the cause of this? what would be a mis-diagnosis
could be seen as recurrent caries however this is not regular and thin
caused by edge enhancement algorithm that intensifies difference in grey scale
206
what is PACS and what are its advantages
picture archieving communication system
Images can be instantly available in any location, not just the hospital
Images can be viewed simultaneously at different locations
Images cannot get lost
Film stores are eliminated
Imaging can be integrated with other electronic records
207
what is a key advantage of PACs regarding other imaging
it can store images of different origin e.g. xrays/CT//MRI/Ultrasound/siologram all in one format that can be viewed on any computer
DICOM - digital imaging and communication in medicine
208
what is DICOM
digital imaging and communications in medicine
| storage format of medicinal imaging including xrays on PACS
209
what is RIS
radiology information system
| stores data regarding previous imaging investigations allowing comparisons
210
if we were to use the fastest film speed, how much more radiation dose do we give with film than digtial
even with the fastest F speed film, this is still 2x more dose than CCD/CDAS
211
how can we improve radiographic quality assurance
keep record of mistakes/poor audit quality
when doing radiograph report record audit quality
yearly calibration of machines
check PSP plates for scratches
use correct techniques for patient placement
use correct dosage for set radiographs
212
where would we expect to find the MAS on a radiograph
maxillary air sinus
| above the roots/apices of upper premolars/molars
213
what are small well circumscribed 1mm diameter radiopacities as the root of premolars/molars? sometimes spikey
dense bone islands
214
how demineralized must a lesion be to be picked up on a radiograph?
30-40%
215
how much larger is a lesion compared to its radiographic size
~25%
216
what pulpal defect often accompanies caries?
deposition of secondary reactionary dentine = receeding pulpal horn
217
why is occlusal caries hard to detect on bitewing radiographs
superimposition of cusps makes it hard to see the fissure pattern (where caries occurs)
218
if we can see a circular radiolucency in the middle of the tooth interacting with the pulp however the pulpal chamber has a well defined wall, what is this?
smooth surface caries (buccal or lingual/palatal)
219
what is cervical burnout and how can we tell root caries
the edge enhancement between crown and root forms a small radiolucency around the crown giving impression of caries
if there is still the curvature of the root with integrity, this is not root caries
220
what is the earliest sign of periapical periodontitis
widening of the periodontal ligament followed by loss of lamina dura
221
what is the thin white line that circumscribes a tooth root and what is the dark radiolucency between this and the root
lamina dura
| periodontal ligament
222
how long after PDL inflammation does it take to see radiographic periodontal spcae widening
10 days
223
a seemingly spreading radiolucency/radiopacity around the apex of an infected root. what is this? which is more common
rarefying osteitis - dissolution of bone due to inflammation
sclerosing/condensing osteitis - trying to protect
outcome of inflamed peri-apical periodontium
rarefying osteitis is 95% of non vital teeth, 5% sclerosing osteitis
224
a 1cm diameter well defined radiolucency surrounds the apex of a tooth, what is this? why has this occurred
periapical granuloma
| chronic inflammation of periapex causes fibrovascular granulation tissue to be stimulated
225
a well defined radiolucency, larger than 1cm in diameter, circumscribed with a radiopaque line at the apex of a dead tooth is what?
a radicular cyst - result of untreated periapical granuloma from chronic inflammation of the periapical periodontal tissue
226
what is osteomyelitis and how does it present radiographically
infection of the marrow of the mandible leading to radiolucencies dotted around the mandible
227
radiographically how big should the gap between alveolar crest and CEJ be~ in health periodontium?
1.5mm
228
for staging bone loss radiographically, where do we measure from and how much below this point classes as stage 1
CEJ
<2mm or <15% reduction
therefor 3.5mm under CEJ is acceptable for stage 1
229
if we can see a radiolucency in the middle of the alveolar bone between teeth, what is this
interdental crater
| crater between lingual and buccal plate
230
what is preferential bone loss of lingual and buccal cortices and how does this represent radiographically. How would you tell which (lingual or buccal) cortical bone is more resorbed
where either the lingual or buccal cortical bone has resorbed more
2 different lines of contrast showing where there is 1 or 2 cortical bones present
cant tell radiographically, obvious with a periodontal probe
231
adjacent to a tooth we can see radiographically two separate lines of radiolucency. what is this
preferential bone loss of either lingual or buccal cortical plate
232
where would we often find supernumery teeth
small, at midline of maxilla radiographically
233
we can see a 90 degree bend in a tooth, what is this?
dilaceration
234
we can see short roots, long crowns and pulp chambers, low lying furcations. What is this
taurodontism (or dentinogenesis)
235
we can see very thin enamel radiographically and clinically the enamel seems to be flaky. what is this and what causes it
amelogenesis imperfecta
| amelogenin defect dominant autosomal defect
236
we can see lots of small radiolucent 'blobs' near the root of a forming tooth, what is this?
compound odontoma
237
we can see a large radiopaque mass around a forming tooth. What is this and where does it normally occur
complex odontoma
| posterior mandible
238
what radiograph captures lower 3-3? what is often seen in the bone below lower incisors
mandibualr anterior peripaical radiograph
| lingual foramen
239
why would we take a CT over an OPT
gives a 3D image to gain better understanding
240
how much exposure time do we give for a adult/child anterior/posterior PA/BW
adult post: .16s
adult ant: .12s
child post: .12s
child ant: .1s
241
what might a radiolucency on the mesial of the 4 be?
canine fossae so less bone structure
242
what is an artefact on a radiograph
something of unknown origin - may not be there, may be an unknown object
243
what is a J shaped lesion indicative of
vertical root fracture
244
what is cephalometry
Cephalometry is the measure of the planes of the skull. There is the horizontal, vertical and transverse plane of the head but cephalometry only allows us to measure horizontal and vertical, not transverse.
245
what are the standard distances for a cephalometric image
5ft STO and 1ft OTI
246
what are some cephalometry validity and reproducibility errors
validity:
- positioning of head
- superimposition
- magnification as 2D image of 3D object
reproducibility:
- thickness of pencil
- blurring due to movement
- variation of film contrast
- inconsistency of identifiable landmarks
247
what do we do firstly after we have taken a lateral ceph radiograph
trace the hard and soft tissues with a thin pencil
248
what do we trace on a lateral ceph
```
border outline of soft tissues
mandible
pituitary fossa
nasal spine (ANS_PNS)
maxillary/mandibular incisor
nasal bone
```
249
on a lateral ceph, what is the point: S
sella, midpoint of pituitary fossa
250
on a lateral ceph, what is the point: N
Nasion
| most anterior part of the frontonasal suture (top of nasal bone)
251
on a lateral ceph, what is the point: A
deepest concavity of the anterior maxilla
252
on a lateral ceph, what is the point: B
deepest point in the concavity of the mandible
253
on a lateral ceph, what is the point: ME or M
menton
| lowest part of the mandibular symphysis
254
on a lateral ceph, what is the point: Go
consturcted point of the intersection between tangents of the ascending ramus and the mandibular symphysis
most inferior point of the mandibular symphysis
255
on a lateral ceph, what is the point: U1 and L1
tip of upper and lower incisors
256
what does the SN line go between and signify
S point = midpoint of pituitary fossa
N point = most anterior point of frontonasal suture
SN = cranial base line
257
on a lateral Ceph; what is the average SNA angle and what doe this signify
between midpoint of pituitayr fossa (S), N - anterior part of frontnasla suture and A, deepest concavity of the maxilla
81 degrees +/- 2 degrees
relationship between cranial base and maxilla
258
what is the ANB angle, what is its average and what does it signify
between A (deepest concavity of maxilla), B (deepest concavity of mandible) and N (most anterior part of frontonasal suture)
average 2-4 degrees
signifies relationship between mandible and maxilla
259
what is the SNB angle, average angle and what does it signify
angle between S (midpoint of pituitary fossa), N (most anterior part of the frontonasal suture) and B (deepest concavity of mandible)
average 78 degrees -/+ 2 degrees
signifies mandible relationship with cranial base
260
what is the MMPA on a ceph and how do we find it and what should it be
mandibular maxillary plane angle
find intersection between ANS-PNS line and lower border of mandible
27 degrees
261
what should the angle between maxillary plane and upper incisors be (on a ceph)
109 degrees
262
what should the mandibular plane form with the lower incisors
92 degrees
263
which teeth do we trace on lateral cephs
central incisors
| NOT laterlas or canine
264
why might we radiograph sound dentition with an impacted molar
impacted molar is a risk factor for caries
| interproximal caries cannot be seen clinically
265
what is the normal recall for bitewings for sound dentition
2-3 years
266
what is the recall for impacted molars
every year
267
What standard exposure does a pt get from a bitewing
0.005 mSv
268
What is the radiation from an OPT and BW
0.01mSv OPT
| bitewing 0.005mSv
269
What is the maximum annual dose for public, non classified workers and radiation workers
Workers 20mSv
Non classified 6mSv
Public 1mSv
270
How do we decrease dose for ALARP
```
Quickest possible film speed
Filtration/attenuation
Lead lined column
Collimation
Optimised kEv and mAh
```
