Radiology Flashcards
(197 cards)
1
Q
Why are radiographs useful?
A
- provide ability to see structures within the body. particularly mineralised tissues
- can show normal anatomy and pathology
- aid diagnosis, treatment planning and monitoring
2
Q
Name 3 different types of intra-oral radiographs?
A
- periapical
- bitewings
- occlusal
3
Q
Name 2 different types of extra-oral radiographs?
A
- panoramic
- lateral cephalograms
4
Q
What are the Electromagnetic Radiation properties?
A
- no charge
- no mass
- always travel at the speed of light (3x10^8 ms^-1)
- can travel in a vacum
5
Q
What is the electromagnetic spectrum?
A
different types of EM radiation which have different properties dependent on its (energy/wavelength/frequency)
Typically divided into 7 main groups
6
Q
Name the 7 groups of the EM spectrum from highest energy to lowest energy?
A
- gamma ray
- x-ray
- ultraviolet
- visible
- infrared
- microwave
- radio
7
Q
What is frequency a measure of?
A
- how many times the wave repeats per unit time
- measured in Hz
- one Hz = one cycle per second
8
Q
what speed is all electromagnetic radiation?
A
3x10^8ms^-1
9
Q
What happens if the frequency of EM radiation increases?
A
the wavelength must decrease and vice verse as S= F x W and speed is always 3x10^8
10
Q
What is energy measured in?
A
electron volts (eV)
1V = energy gained by 1 electron moving across a potential difference of 1 volt
11
Q
What is the range of x-ray photon energies?
A
124eV - 124keV
12
Q
What is the difference between hard and soft x-rays?
A
hard x-rays = higher energies (>5keV) and able to penetrate human tissues
soft x-rays = lower energies and easily absorbed by tissues
13
Q
How are x-rays produced?
A
- electrons are fired at atoms at a very high speed
- on collision the kinetic energy of these electrons is converted to EM radiation (ideally x-rays) and heat
- the x-ray photons are aimed at a subject
14
Q
What is the mass of an atom?
A
Mass Number (A) = number of protons + neutrons
15
Q
What is the atomic number of an atom?
A
Atomic number(Z) = number of protons
16
Q
How do electrons fill spaces in there electron shells?
A
- try fill spaces in the inner shells first before moving to the next shell
17
Q
What is the calculation for working out how many electrons each shell can hold?
A
2n^2 where n= shell number
- k=1, L=2 and so on
18
Q
What is electrostatic force?
A
-ve charge of electrons are attracted to the overall positive charge of the nucleus holding the electrons within their shells
19
Q
What is Binding Energy?
A
The amount of energy required to remove an electron from its shell ( must exceed the electrostatic force)
20
Q
What electron shell has the greatest binding energy and why?
A
Electrons in K (inner most) shell have the highest binding energy as they are closer to the nucleus and have a greater electrostatic force
21
Q
What effect does the atomic number have on the binding energy?
A
The higher the Z (more positively charged the nucleus) the greater the electrostatic force and the greater the binding energy
22
Q
What would be the energy required to move an electron to a more outer or inner shell?
A
moving an electron to a more outer shell equals the difference in the binding energies of the 2 shells and if the electron drops to a more inner shell then this specific energy is released( possibly in the form of X-ray photons if sufficient energy)
23
Q
X-ray production requires a unidirectional current but x-ray units are powered by mains electricity which is an alternating current. How is this problem solved?
A
X-ray units have generators which modify AC so that it mimics a constant DC which is a process know as rectification
24
Q
What is a voltage?
A
The difference in electrical potential between 2 points in an electrical field and how forcefully a charge will be pushed through an electrical field
25
What is a transformer and what is there function in the X-ray unit?
- Alter the voltage from one circuit to another
- 2 are found in the x-ray unit
1. mains - x-ray tube (cathode-anode)
2. mains - filament
26
What is the difference between a step up and stepdown transformer in the x-ray unit?
Step up transformer - increases the potential difference across the x-ray tube (60-70kV) and current reduced to milliamps (MA)
step down transformer - decreases the action potential across filament (10V) and current 10 amps
27
What is the X-ray beam made of?
millions of x-ray photons travelling in straight lines diverging from the x-ray source
28
What effects the intensity of the x-ray beam?
number and energy of the photons ie the current in filament (mA) and potential difference across x-ray tube (kV)
29
What occurs to the intensity of the x-ray dose by increasing the distance of the object from the x-ray source?
intensity decreases as beam is divergent so less photons hit the object per unit ^2
30
What is inverse square law in relation to x-ray dose/intensity?
Intensity of X-ray beam is inversely proportional to the square of the distance between the X-ray source & the point of measurement
Intensity 𝖺 = 1/distance^2
31
If a patient standing in the X-ray beam gets a dose of 4 grays at a distance of 1 metre (from the X-ray source), what will the dose be at 4 metres?
0.25Gy
32
What are the 2 main components of the cathode (-) in the x-ray tube head?
filaments and focusing cups
33
What is the filaments in the cathode made of?
coils of wire (tungsten)
34
how are electrons released from atoms in the filament (wire)?
thermionic emission
35
Why is tungsten used to make the filament?
- high melting point (3422 degrees)
- high atomic number (Z=74) therefore lots of electrons per atom
- malleable
36
What is the cathode focusing cup made of?
molybdenum
37
What is the function of the cathode focusing cup?
- negatively charged therefore repels electrons released at the filament
- shaped to point electrons at a small point on the anode target
38
Describe the cathode-anode relationship?
- high voltage electricity passes through x-ray tube (high potential difference between - cathode and + anode)
-electrons released at filament are aimed and attracted towards the positive anode accelerating to half the speed of light
- increasing action potential increases acceleration and therefore the kinetic energy released upon colliding with the anode
39
What does the unit eV stand for and what does it measure?
- Electron volts
- measures the kinetic energy gained per electron as the accelerate from cathode to anode
40
What determines the amount of kinetic energy an electron gains travelling from the cathode to the anode?
-the potential difference across the x-ray tube
- eg if the potential difference is 70kV the kinetic energy gained per electron will be 70keV
41
What material is used for the anode target in an x-ray?
tungsten
42
Why is tungsten used for the anode target?
- high melting point
- produces x-ray photons of useful energies
43
What is the precise area on the anode target where electrons collide and x-rays are produced called?
focal spot
44
What is the function of the heat dissipating block which the anode target is embedded into?
- heat produce by collision at the anode target dissipates into the metal block and reduces the risk of overheating which could cause damage to the target
45
What is the heat dissipating block on the anode target made of?
copper
46
What is the penumbra effect?
blurring of the radiographic image due to a focal spot not being a single point (but rather a small area)
47
Why is the vocal spot on the anode angled?
- <1% of kinetic energy from the electrons is converted to X-ray photons whereas ~99% is converted to heat
↓ focal spot size = ↑ image quality but ↑ heat concentration
Solution: angled target
Increases the actual surface area where electrons impact
↑ better heat tolerance
Reduces the apparent surface area from where the X-ray beam
is emitted
↓ penumbra effect
48
What is the function of the glass envelope that surrounds the cathode and anode?
- supports cathode and anode
- maintains a vacuum (electrons unhindered by gas molecules)
- leaded glass to absorb x-ray photons not travelling in the desired direction ( has small un-leaded window for desired x-ray beam)
49
What is the function of the metal shielding in the x-ray tube head?
- absorbs x-rays
- usually lead
- window where x-ray beam exits
50
what is the function of the oil in the x-ray tube head?
dissipates heat produced by x-ray tube by thermal convection
51
What is the function of aluminium filtration in the x-ray tube head?
- Removes lower energy (non-diagnostic) X-rays from beam as Low energy photons would all be fully absorbed by patient’s tissues & increase patient dose but not contribute to image
52
What is the minimum thickness of aluminium required if x-ray photons are <70kV?
1.5mm
53
What does fsd stand for?
Focus to skin distance
54
What is the function of a spacer cone?
- dictates the fsd ensuring a consistent technique
- indicates the direction of the beam
55
What occurs if you increase the fsd?
- reduces divergence of beam therefore less magnification on image
- reduces intensity of x-ray beam
56
What is the required fsd when using > or = 60kV?
200mm
- measured from focal point on anode
57
What is the function of a collimator on the spacer cone and what are the benefits of using it?
- lead diaphragm attached to spacer cone which crops x-ray beam to match shape and size of x-ray receptor
- reduces patient dose
- convert circular cross section to rectangular cross section
- can reduce radiation surfaces by 50%
- reduces scatter improving image contrast
58
When using a size 2 receptor what area size should the rectangular collimator reduce beam area to?
50mm x 40mm but preferably < 45mm x 35mm
59
What percentage of the electrons bombarding target produces heat and why?
99%
- due to there being a much larger number of outer shell electrons in tungsten
- bombarding electrons reach tungsten outer shells and either
1. Comes into close proximity & is then decelerated & deflected
Note: both negatively charged
2. Collides & is deflected
- bombarding electrons lose kinetic energy which is released as heat
60
How is the heat dissipated in the x-ray tube head?
tungsten target - copper block- oil in tube head-air
61
How are x-rays produced at tungsten target?
- Bombarding electrons pass close to target nucleus, causing them to be rapidly decelerated and deflected
- this loss of kinetic energy is released as x-ray photons (1%)
62
What causes there to be X-ray photons at various different energies to be produced at the target?
- continuous radiation
- the greater the proximity of the electron to the nucleus of tungsten atom the greater the deceleration and deflection therefore the greater energy released
63
How are lower energy non diagnostic x-ray photons removed from the beam?
Aluminium filtration
64
Describe characteristic radiation?
- Bombarding electron collides with an inner-shell electron & either displaces it into a more peripheral shell (excitation) or removes it completely (ionisation)
- The remaining orbiting electrons rearrange themselves to re-fill the innermost shells
- When an electron “drops” to a lower shell it loses energy which is emitted as a photon of specific energy
- Values depend on the element involved (eg. tungsten)
65
In characteristic radiation what does the photon energy equate to?
- the difference in energies of the 2 shells involved when the electron drops to a lower shell
- the energy difference is different for each atom
66
What is the binding energy of the inner most (K) shell of tungsten?
69.5keV
- hence why x-ray tubes operate at 70kV
67
What two types of radiation make up the x-ray beam?
continuous radiation + characteristic radiation
68
what are the key differences in continuous radiation and characteristic radiation?
continuous
- Produces a continuous range of X-ray
photon energies
- Maximum photon energy matches the peak voltage
- Bombarding electron interacts with nucleus of target atom
Characteristic
- Produces specific energies of X-ray photon, characteristic to the element used for the target
- Photon energies depend on the binding
energies of electron shells
- Bombarding electron interacts with inner- shell electrons of target atom
69
What 3 ways can photons in a diagnostic x-ray beam interact with matter?
- Transmission (passes through matter unaltered)
- absorption (stopped by the matter)
- scatter ( changes direction)
70
What is attenuation?
reduction in x-ray intensity
71
What two factors cause attenuation of the x-ray beam?
Absorption (energy absorbed by tissue)
scatter (photon deflected by matter)
72
What primarily effects the number of photons in x-ray beam?
the current in the filament (mA)
73
What primarily effects the energy in the x-ray beam?
the potential difference across the x-ray tube (kV)
74
What two factors effect the intensity of the x-ray beam?
energy and number of photons
75
If there is minimal, partial and complete attenuation of the x-ray beam what colours would you see on the radiograph
minimal - black
partial - grey
complete - white
76
What are the 2 specific attenuation reactions photons in the x-ray beam can have with the subject it is directed at?
- photoelectric effect
- compton effect
77
Describe the photoelectric effect?
- photon in x-ray beam interacts with inner shell electron in subject resulting in complete absorption and creation of a photoelectron
- occurs when energy of the incoming photon is equal to or greater than the binding energy of the inner shell electron
- photon energy overcomes binding energy resulting in inner shell electron being ejected and now called a photoelectron
78
Does the photoelectric effect predominate in high or low energy photons and explain why?
- predominates in low level photons as tissues have relatively low binding energy
79
What is the negative impact that photoelectrons can cause?
photoelectrons can ionise and can cause damage to adjacent tissues
80
What is the calculation for the probability of a photoelectric effect occurring?
photoelectric effect = (p x Z^3) divided by E^3
where
Proportional to atomic number cubed (Z3)
Inversely proportional to photon energy cubed (1 / E3)
Proportional to physical density of material (ρ)
81
Describe the compton effect?
- Photon in X-ray beam interacts with outer shell electron in subject, resulting in partial absorption & scattering of the photon & creation of a recoil electron
- Occurs when energy of incoming photon is much greater than binding energy
of electron
- Some photon energy transferred to electron to overcome binding energy & provide kinetic energy
82
is Compton effect more lightly to happen to high or low energy photons and why?
- high energy photons and outer shell electrons as energy from the photon is much greater than the binding energy of a outer shell electron
83
What is the electron called that is ejected from matter during the compton effect?
recoil electron
- this can ionise and damage adjacent tissues
84
What happens the the photon after it interacts with an outer shell electron in the Compton effect?
- photon loses energy and changes direction (scattered)
- scattered photon can undergo photoelectric effect or compton effect interactions
85
What direction of scatter are high and low energy photons most likely to be deflected?
high energy = forward scatter
low energy = backwords scatter
86
Why is it important that a controlled area is set up around the patient when taking x-rays?
- to avoid unnecessary exposure to the x-ray photons via scattered photons
87
What is the effect of scattered photons on the x-ray image?
- photons that are scattered sideways, backwords or very obliquely forward will not reach the receptor and will not have an effect on the image
- photons that are scattered slightly obliquely forward that reach the receptor cause darkening in the wrong places of the image
- this results in fogging of the image and reduces image contrast and quality
88
What 2 things can effect the probability of the compton effect occuring?
- weakly proportional to photon energy
- proportional to density of material
89
What effect will increasing photon energy have the probability of compton effect and the radiographic image?
- minimal effect on the likelihood of the Compton effect
- increases forward scatter reaching receptor therefore increases fogging of the image
90
What are the benefits of using a collimator when taking x-rays?
1. decreases surface area irradiated
2. decreases volume of irradiated tissue
3. decreases the number of scattered photons produced in tissue
4. decreases scattered photons interacting with receptor
5. decreases loss of contrast on radiographic image
6. reduces patient radiation dose and radiation being released into the surroundings
91
What impact does the photoelectric and compton effects have on radiation dose and image?
photoelectric effect
- deposits all photon energy into tissue
- increases dose but is necessary for imaging
Compton effect
- deposits some photon energy into tissue
- increase dose but increase scatter which does not contribute to image
- increase in dose to operator
92
What effect will lowering the kV in the x-ray unit have?
- lower x-ray tube potential difference
- overall lower energy photons produced
- increase in photoelectric effect
- increase contrast between tissues with different Z
- but increases dose absorbed by patient
93
What effect does raising the kV on x-ray tube have?
- Higher X-ray tube potential difference (kV)
- Overall higher energy photons produced
- ↓ photoelectric effect interactions (+ ↑ forward scatter)
- ↓ dose absorbed by patient
BUT
- ↓ contrast between tissues with different Z
94
What is the UK guidance for kV for intraoral x-ray units?
60kV-70kV
95
How does ionisation radiation directly damage DNA?
Radiation interacts with the DNA molecule or another important part of the cell
96
How does ionisation radiation indirectly damage DNA?
- Radiation interacts with water in the cell, producing free radicals which can cause damage
- Free radicals are unstable, highly reactive molecules
97
What type of radiation usually causes double stranded DNA breaks?
Alpha particles
98
What factors determine the biological effect of DNA damage?
- type of radiation
- radiation dose
- time exposed to radiation dose (dose rate)
- tissue or cell being irradiated
99
Is a high or low dose rate less damaging to a cell and why?
- low as it gives time for the cell to repair any DNA damage before further damage occurs
100
What determines the radio sensitivity of tissues?
- the function of the cells that make up the tissue
- if the cells are actively dividing
101
explain why stem cells are more radio sensitive than differentiated cells?
stem cells divide frequently to produce new cell populations where as differentiated cells do not exhibit mitotic activity
102
What tissues are highly radio sensitive?
- bone marrow
- lymphoid tissue
- gastrointestinal
- gonads
- embryonic tissue
103
which tissues are moderately radio sensitive?
- skin
- vascular epithelium
- lung
- lens of eye
104
Which tissues are least radio sensitive?
- CNS
- bone and cartilage
- connective tissue
105
What are the possible outcomes of a cell after DNA mutation?
- mutation repaired (viable cell)
- cell death
- cell survives but is mutated (cancer)
106
What is the units of absorbed dose?
Gray (Gy)
- measures the amount of energy deposited into tissue
107
What is the calculation and units for equivalent dose?
- absorbed dose multiplied by a weighting factor depending on the type of radiation
- sieverts (Sv)
108
What is the weighting factor of alpha particles?
20
109
What is the weighting factor for beta, gamma and x-rays?
1
110
What model is used to determine the long term effect of radiation on the population?
linear no threshold model (LNT)
111
What does the LNT model presume?
- It assumes the damage is directly proportional (linear) to radiation dose
- It assumes that radiation is always harmful with no safety threshold
112
What are the two types of biological effects of radiation?
Deterministic and stochastic
113
Explain what the deterministic effect is?
- tissue reactions where the severity of the effect is related to dose received
- only occur above a certain threshold
- unusual to see in radiology *dose not high enough)
114
explain what the stochastic effect is?
the probability of occurrence is related to dose received
115
What are the two categories that stochastic effects can be divided into?
somatic - results in disease or disorder (cancer)
genetic - abnormalities in descents
116
What is the effect of radiation dose on pregnancy?
- radiation exposure can kill or damage enough cells for the embryo to undergo absorption
117
What dose would induce lethal effects to an embryo immediately after conception/implantation?
100mGy
118
During organogenesis what radiation dose would cause lethal effects to the embryo?
250mGy
119
Are dental x-rays contraindicated in pregnant patients?
- no because the dose to the foetus is so low
- the foetus must not be irradiated inadvertently nor should the x-ray beam be directed at the abdomen
120
What is the risk of cancer naturally and per 1mGy of exposure in children up to the age of 15?
naturally = 1 in 650
per 1mGy of exposure = 1 in 13,000
fatal cancer per 1mGY = 1 in 40,000
121
What is the estimated annual background dose of radiation?
2.2mSv
122
Name 4 sources of background radiation?
- radon gas from ground
- gamma rays from ground/buildings
- cosmic rays
- food and drink
123
what makes up 50% of background radiation?
radon gas
124
What percentage of background gas is natural and artificial?
84% natural
16% artificial
125
What is the lifetime risk of cancer per intra-oral radiograph (0.005mSv)?
1 in 10million- 1 in 100 million (negligible risk)
126
What distance should a controlled area be from the x-ray tube head?
at least 1.5m surrounding the tube head
127
What are the 3 basic concepts of radiation protection?
justification
optimisation - as low as reasonable practicable (ALARP) taking into account economic and social factors
dose limitation - system of acceptable individual dose limits
128
What methods are used to reduce patient dose during dental x-rays?
- Use E speed film or faster (fewer X-ray photons required)
- Use a kV range of 60kV to 70kV
- The focus to skin distance should be >200mm
- Use rectangular collimation
129
What are diagnostic reference levels (DRL)?
- Legislation requires Employers to have established dose levels for typical examinations for standard sized patients
- They are a comparative standard that is used in optimisation
- They are compared to national reference levels
- Individual X-ray units are compared to the DRLs and national reference levels
130
What is the current DRLs for intra-oral x-rays in adults?
Adult: 0.9mGy (digital sensors) and 1.2mGy (phosphor plates and film)
131
What is the current DRLs for intra-oral x-rays in children?
Child: 0.6mGy (digital sensors) and 0.7mGy (phosphor plates and film)
132
How can you reduce damage and teeth marks on CR plates?
Reduce damage by inserting the plates between two plastic sheets Damaged detectors should be cleaned or replaced if necessary
133
What are the 2 types of digital receptors used in dentistry?
- phosphor plate
- solid state sensor
134
What are the two different type of film receptors in dentistry?
- direct action
- indirect action
135
What is an x-ray shadow?
- when an x-ray beam passes through an object some of the photons are attenuated causing an x-ray shadow
- the image receptor detects this shadow and uses it to create an image
136
What causes the various shades of grey on the x-ray image?
- the x-ray receptor measure the x-ray intensity at defined areas (grid)
- each box on the grid can only be one shade and is given a value usually from 0-255 depending on the intensity of the x-ray beam onto that box
- 0 = black and 255 = white
137
What is the grid of squares called on the x-ray image?
pixels
138
If you increase the amount of pixels on a receptor image what will it improve?
detail, resolution and accuracy of image
139
What are the limitations with increasing pixels size?
- more storage space required to store the digital image (increase cost)
- manufacturing challenges with digital receptors limit how small they can make the pixels
140
Relating to the greyscale bit depth, how many bits are radiographs processed in?
8 bits (2^8)
= 256 shades of grey
141
What is the digital imaging format for radiographic images?
DICOM
- digital imaging and communications in medicine
142
What are the benefits of using the digital imaging format DICOM?
- allows imaging to work between different software machines, manufactures, hospitals and countries with compatibility issues
- can transmit, store, retrieve, print, process and display image
143
What other important information does DICOM store?
- patient ID
- exposure settings
- date of image
144
What system is used in NHS dentistry to store digital images (x-rays)
PACS
- picture archiving and communication system
145
What are the main components of PACS?
- input by imaging modalities ( plain radiographs, MRI, CTs and US)
- secure network for the transmission of patient information
- workstations for interpreting and reviewing images
- archives for the storage and retrieval of images and reports
146
What sort of environment should you view radiographs in?
- subdues lighting
- avoid glare
147
What 4 things on your monitor are important when viewing digital radiographs?
- clean
- adequate brightness
- suitable contrast level
- adequate display resolution
148
What can be used to assess the resolution, contrast and brightness of your monitor?
SMPTE test
- society of motion pictures and television engineers
149
How is an image created using phosphor plates?
Within the patient’s mouth:
1. Receptor exposed to x-ray beam
2. Phosphor crystals in receptor excited by the x-ray energy, resulting in the creation of a latent image
Within the scanner:
3. Receptor scanned by a laser
4. The laser energy causes the excited phosphor crystals to emit visible light
5. This light is detected & creates the digital image
150
Name two types of solid state sensors?
- Charge coupled device (CCD)
- complimentary metal oxide semiconductor (CMOS)
151
How are multiple use digital receptors prevented from cross contamination between patients?
1. single use plastic covers are placed over sensor
- adhesive sealed plastic covers for PP
- long plastic sleeve for wired SSs
2. receptor still disinfected between use
152
how should you hold receptors to prevent damage?
hold them by the edges not the flat surface
153
What occurs on the image if there is finger prints, bending, scratches or tears on the receptor?
white areas where the dame has occurred (no emulsion left)
154
What are the differences between phosphor plates and solid state sensors?
phosphor plates are:
- thinner, lighter and more flexible
- wireless, more stable and comfortable
- latent image needs to be processed in the scanner separately (slower than SSS)
- sensitive to room light
- handling similar to film
Solid-state sensors:
- Bulkier & rigid
- Usually wired
- Smaller active area (for same physical area of receptor)
- No issues with room-light control
- Arguably more durable so replaced less often
- More expensive
155
Describe the structure of the intra oral film packet?
- radiographic film surrounded by protective black paper
- there is a sheet of lead foil at the back of the film
- the film, black paper and lead foil is surrounded by the outer rapper
156
Describe the structure of the radiographic film itself?
- transparent plastic base covered in adhesive which sticks the emulsion to the base (both sides of base)
- there is a protective coat of clear gelatin surrounding the emulsion
157
What type of crystals are embedded in the gelatin layer of the radiographic film?
silver halide crystals (usually silver bromide)
158
How do silver halide crystals in radiographic film make an image?
- the crystals (pixels) become sensitised upon interaction with the x-ray beam (and visible light)
- during processing sensitive crystals are converted to particles of dark metallic silver
- non-sensitized crystals are removed (white areas)
159
What is the function of the lead foil at the back of the film receptor?
absorbs some excess x-ray photons:
- those in the primary beam continuing past the receptor
- those scatter by patient tissues and returning back to film
160
If there was an embossed patter on the film image what would this indicate?
- the receptor was placed the wrong way round and the embossed lead foil has been captured on the image
161
what effect does increasing film speed have on radiation and image quality?
- decreases amount of radiation needed t produce an image
- larger silver bromide crystals are needed to increase film speed which in turn reduces image quality
162
When and why are intensifying screens used?
- indirect action film for extra oral radiographs
- reduce radiation dose but also reduce detail of image
163
What are the different methods of film processing?
- manual
- automated
- self developing
164
What are the 5 common steps in film processing?
1. developing
2. washing
3. fixing
4. washing
5. drying
165
What occurs during each step during film processing?
1. developing- coverts sensitized crystals to dark metallic matter
2. washing - removes residual developer solution
3. fixing - removes non-sensitized crystals
4. washing- removes residual fixer solution
5. drying - removes water so that film is ready to be handled/ stored
166
Describe the process of a manual film processing cycle?
- a person dips film into different tanks of chemicals
- this is done at precise concentration and temperatures for specific periods of time
- must be carried out in a dark room with absolute light tightness and adequate ventilation
167
What are the advantages and disadvantages of using an automated film processing cycle?
- faster
- more controlled
- avoids need for dark room
- more expensive
168
in an automated processing film cycle how is the developer removed from the film?
sponge rollers squeeze it out
169
How do you open a film packet to place into the automated processing machine?
1. disinfect the surface of the packet
2. hold the packet under the hood of the processing unit
3. peel back the flap of the outer wrapper
4. fold back lead foil
5. pull back paper flab
6. hold film by edges
7. insert film into processor slot
170
What are the advantages of a self developing film?
- no darkroom or processing facilities required
- faster
171
what are the disadvantages of a self developing film?
- poor image quality
- image rapidly deteriorates over time
- no led foil
- easily bent
- expensive
- difficult to use in positioning holders
172
what are the potential causes of a pale film image?
- radiation exposure factor too low
Developing issue
- film removed from solution too early
- solution too cold
- solution too dilute
(opposite of these will make the image darker)
173
What cause a radiographic film image to be greenish -yellow or milky looking?
- inadequate fixing ( removal of non-sensitized crystals)
- image will become brown over time
174
What would inadequate washing of the developer cause on a image?
black spots on image that shouldn't be there (image will continue to develop)
175
what would inadequate washing of the fixer cause on a image?
lighter spots on the image
176
What are the advantages of digital images compared to film?
- no need for chemical processing
- easy storage and archiving of images
- easy back up of images
- images can be integrated into patient records
- easy transfer/ sharing of images
- images can be easily manipulated
177
What are the disadvantages of digital imaging compared to film?
- Worse resolution risk of pixelation
- Requires diagnostic-level computer monitors for optimal viewing
- Risk of data corruption/loss (solved by backing up)
- Hard copy print-outs generally have ↓ image quality
- Image enhancement can create misleading images
178
Why can lateral cephalograms be used to monitor changes over time?
- standardised and reproducible
- patient is positioned a set distance from the x-ray beam and receptor
179
What is a cephalostat used for?
- holds head at correct angle
- stabalises head
- establishes correct distances between x-ray forcal spot, patient and receptor
- reduces magnification and distortion of the image
180
How far should the receptor be from the x-ray focal spot when taking a lateral ceph?
1.5-2m
181
Soft tissues show up poorly on a lateral ceph due to exposure settings being set for hard tissues, what is the solution to this problem?
- Place an aluminium wedge filter in the unit to attenuate the specific area of the beam exposing the facial soft tissues
OR
- Use software to enhance the soft tissues post-exposure
182
What 2 pieces of equipment should be used to reduce patient dose when taking a lateral cephalogram?
- collimator
- thyroid collar
183
When would an oblique lateral radiograph be used?
Useful if patient unable to tolerate intra-oral radiographs & unable to stay still or fit in panoramic unit (e.g. young children)
184
When would you used radiographic localisation?
to determine the position of a structure or pathological lesion in relation to other structures
185
What radiographic views are at right angles to each other and can be used for radiographic localisation?
- panoramic and true mandibular occlusal
- periapical and true mandibular occlusal
- CBCT
186
What is parallax?
an apparent change in the position of an object caused by a actual change in the position of the observer
187
What radiographs can be used that involves a vertical or horizontal tube shift that would allow radiographic localisation of a structure?
Horizontal
- 2 periapical
- 2 bitewings
- 2 oblique occlusal
Vertical
- periapical/panoramic and maxillary oblique
- panoramic and lower bisecting angle periapical
188
What is a good numonic for radiograph localisation?
my PAL goes with me
- palatal and lingual structures will move in the same direction as the tube shift
- buccal structures will move in the opposite direction
189
What is the purpose of Quality assurance in dental radiology?
- to ensure consistently adequate diagnostic information while keeping dose to patient and others ALARP
190
What are the 3 QA checks on a digital receptor?
- receptor itself
- image quality
- image uniformity
191
What are common signs of damage to a receptor that show up on a radiograph?
phosphor plates - white lines
solid state sensor - white lines and squares
film - black marks or white if emulsion scraped off
192
What is a way of assessing image quality?
step wedge
- over lapping layers of lead foil exposed to normal clinical exposure
- compared against baseline image
193
What are the 3 parts of QA of image quality?
1. image quality rating
2. image quality analysis
3. reject analysis
194
What percentage of digital images and film images should be diagnostically acceptable?
digital = 95%
film = 90%
195
What are the requirements for a diagnostically acceptable bitewing?
- show entire crowns of upper and lower teeth
- minimal overlap
- distal aspect of canine and mesial aspect of last standing tooth
- adequate contrast, sharpness, resolution and minimal distortion
196
What are the requirements for a diagnostically acceptable periapical?
- entire root
- entire crown
- periapical bone
- adequate contrast, resolution and minimal distortion
197
What can cause an image to be to light/ too dark?
- exposure factors
- developing factors (temp, concentration, duration)
- viewing factors (inappropriate light source or display screen)
