Radiology Flashcards
What are the types on intra-oral radiographs?
- Peri-apical
- Bitewing
- Occlusal
What are the types on extra-oral radiographs?
- dental panoramic tomogram (DPT)
- lateral cephalogram
- postero-anterior mandible
- lateral oblique mandible
- occipital-mental views of facial bones
What does a peri-apical radiograph show?
crown to apex, clear distinction between teeth
What does a horizontal bitewing show?
distal edge of 4 to mesial edge of 8, need to see bone levels but not the whole root
What does a vertical bitewing show?
more of the the bone than a horizontal bitewing, but still not the whole root
What does a maxillary occlusal radiograph show?
anterior part of maxilla
What does a mandibular occlusal radiograph show
(lower submandibular occlusal) - shows a plane view of the tooth bearing position of the mandible and the floor of the mouth
What does a DPT do?
X-ray tube rotates around the patient’s head with a constant long exposure of 14 seconds, forming a panoramic image of the patient’s teeth and supporting structures
How well are DPTs tolerated by patients?
can be tolerated by the majority but patient’s body shape can make it difficult
What is a lateral cephalogram?
standardised and reproducible form of radiography used extensively in orthodontics to asses the relationship of the teeth to the jaws and the mandible to the rest of the facial skeleton
can also see soft tissue pattern of nose and lips which is useful in some surgical planning
What is a postero-anterior mandible radiograph useful for showing?
a fracture of the mandible
What is a postero-mandible view usually requested in conjunction with?
a DPT
How is a postero-anterior mandible view taken to show the full extent of a fracture?
2 views taken at right angles to one another
When is a lateral oblique mandible most commonly taken?
in the dental hospital for children that can’t tolerate a bitewing, also on adults with mandibular fracture if a DPT is not available
What does an occipito-mental view show?
fractures of the orbits, maxilla, and zygomatic arches
How is an occipito-mental view taken?
2 views taken - beam angled at 10 degrees, and beam angles at 30 degrees
What is the benefit to taking films erect in occipito-mental views?
can demonstrate fluid levels in the antra
Why do intra-oral views show more detail of the teeth than extra-oral views?
the closer the object is to the receptor, the more detail on the image
Why would you take a peri-apical radiograph?
- detect apical inflammation/infection to include cystic changes
- assess periodontal problems
- trauma-fractures to tooth and/or surrounding bone
- tooth morphology pre-extraction
- presence/position of unerupted teeth
- endodontics
- pre/post apical surgery
- evaluation of implants
What are the 2 intra-oral radiograph techniques?
- paralleling technique
- bisected angle technique
What is the standard intra-oral technique?
paralleling technique
When is a bisected angle technique used?
when patient can’t tolerate a holder in their mouth
- can ask them to hold film in their mouth with their finger (not ideal as exposing finger to radiation
- can also use holder that looks like a lolly pop stick (can also be used during endo procedures)
What are the differences between paralleling and bisected angle techniques?
paralleling:
- uses holders to facilitate positioning
- receptor parallel to tooth
- accurate/reproducible image
bisected angle:
- can be done without a holder
- operator dependent
- not reproducible
What are the 7 main points of paralleling technique?
- uses holders to facilitate positioning
- allows accurate geometry of image
- receptor parallel to tooth
- x-ray beam perpendicular to tooth/receptor
- minimises magnification
- accurate/reproducible image
- holders are bulky and may not be tolerated by patient. can reduce dose to patient by reducing repeats and does not expose patients fingers (unlike bisected angle)
What are the 4 coloured holders, and what are they used for?
blue - anterior
yellow - posterior
red - bitewings
green - endodontic
What are holders made up of?
- a bite-block - retains the receptor
- an indicator arm/rod - fits into the bite-block
- an aiming ring - slides onto the arm to establish alignment of collimator with receptor
In paralleling technique, what is the receptor-tooth relationship?
- the vertical plane of the film should be positioned so that it is parallel to the long axis fo the tooth/teeth
- the horizontal plane of the film must be parallel to the dental arch under examination
What is the effect of the film and tooth not being paralleled vertically?
tooth will appear elongated and roots projected off the top of the receptor
What is the effect of the film and tooth not being parallel horizontally?
teeth appear overlapped, obscuring pathology
In paralleling technique, what is the effect of the x-ray beam being angled too far up?
elongation- teeth will appear elongated
In paralleling technique, what is the effect of the x-ray tube being angled too far down?
fore-shortening - the teeth will appear short and stubby
In paralleling technique, what is the effect of incorrect horizontal angulation of the x-ray tube?
teeth will appear overlapped (same as when the receptor isn’t in the correct horizontal plane)
collumnator (rectangle at end of x-ray tube) should be lined up with aiming ring of the receptor holder
Magnification - what things affect image size?
- x-ray source (focal spot) to receptor distance
- object (tooth) to receptor distance
What is the effect of changing the x-ray source to receptor distance?
further away - image doesn’t diverge as much, more accurate depicition size wise
What is the effect of changing object to receptor distance?
having the object closer to the receptor reduces the divergence of the beam, making the image appear more size accurate
What is the ideal receptor, object and x-ray source distancing?
short tooth-film distance, long source-tooth distance
What are some barriers to good positioning?
- mouth size
- gag reflex
- film size
- digital sensor size and shape
What are the 4 most common film sizes?
0, 1, 2 and 4
What film size would you use for an adult anterior periapical?
0, 1
What film size would you use for an adult posterior periapical?
2
What film size would you use for an adult bisecting angle periapical?
2
What film size would you use for an child anterior periapical?
0
What film size would you use for an adult posterior periapical (deciduous and permanent)?
deciduous - 0
permanent - 2
What film size would you use for an adult bitewing?
2
What film size would you use for an child bitewing (under 10yo and over 10yo)?
under 10yo - 0 or 1
over 10yo - 2
What is the domestic electricity supply (volts, hertz, amp)?
220/240 volts
50 hertz
13 amp current (usually)
In an x-ray machine, where is the domestic electricity supply converted?
the tube head
What is the filament - cathode?
very fine wire made of tungsten - high melting point, high tensile strength (can be pulled into fine wire)
What current is passed along the cathode? How is this made possible
8-10mA
13amp current needs to pass through a step down transformer - coil of copper wires, in tube head, about he size of a small fist
Why is heat given off during the production of x-rays?
as current passes along a wire the electrons in its atoms become excited and they vibrate - wire gets hot, may give off light
Why are electrons lost from from the outer shells/orbits around the nucleus?
the electrons aren’t held very tightly within their orbit
What do lost electrons form around the cathode?
lost electrons come together to form an electron cloud around the cathode
What is the anode?
small tungsten target embedded in copper
Why is tungsten used for the anode?
it gives rise to x-rays in the wavelength that we require for dental imaging
What is the potential different between the anode and cathode?
usually between 50-90kV, usually 60-70kV
What needs to happen to the domestic electricity supply voltage for the production of x-rays?
domestic electricity supply voltage of about 240V so this needs increased (e.g. to 70kV) - step up transformer in tube head made out of coils of copper
What happens when the electrons from the cathode(-ve) are pulled over to the anode(+ve)?
these electrons are attracted to the positive charge of the anode nuclei, they have high amounts of energy and come to a sudden stop or decelerate and their energy changes form (99% heat, 1% x-rays)
What are the 2 types of x-ray spectra?
- continuous spectrum
- characteristic spectrum
What type of radiation is continuous spectrum?
Bremsstrahlung/breaking radiation
What is the main factor of continuous spectrum radiation?
variety of different wavelengths of x-rays produced
- some of the x-ray photons will have very little energy whereas some will have a maximum amount of energy that this particular tube can produce
What is characteristic spectrum radiation dependant on?
the material used in the anode (e.g. Tungsten)
In characteristic spectrum radiation, what are the x-rays emitted by?
x-rays are emitted by the loss of electrons from the K and L shells
What happens during the production of Bremsstahlung radiation?
a negatively charged electron from the cathode is attracted to the positively charged atom of tungsten within the anode
as it moves round the nucleus, it loses energy (may not lose all of its energy)
much of this energy is given off as heat, as well as some Bremmstahlung radiation
What is scattering?
random change in direction after hitting something
What is absorption, and what does it represent?
deposition of energy in tissues, represents the dose of radiation that the patient receives
What is intensity?
number of x-ray photons in a defined area of the beam
What is the relationship between intensity and distance from the x-ray source?
the further we are from the source of x-ray radiation, the intensity of the photons will decrease
What is attenuation?
reduction in intensity of beam due to scattering and absorption
(weakening)
What is ionisation?
removal of electron from neutral atom to give -ve (electron) and +ve (atom) ions
What is penetration?
the ability of photons to pass through or into tissues/materials
What 4 interactions can occur when x-ray photons hit objects/patients?
- completely scattered with no loss of energy
- absorbed with total loss of energy
- scattered with some absorption and loss of energy
- transmitted unchanged
What is internal scatter?
when radiation is scattered to move down into the patient’s body
Although their overall properties are similar, what is the difference in the way light and x-rays scatter?
when x-ray scatter they go in unpredictable directions once they hit something, whereas light goes in a predictable manner- angle that the light hits is equal to the angle of reflection
What is radiation dose?
the radiation dose is the amount of radiation absorbed by the patient.
low energy photons often are absorbed by soft tissues
What are more likely to cause biological damage, low or high energy photons?
low energy photons as they are absorbed more by soft tissues, whereas high energy photons penetrate more
What type of x-ray spectra is Bremsstrahlung/breaking radiation?
continuous spectrum
What causes characteristic radiation to happen?
an incident electron must have a direct hit with an electron in the k shell
What is an electron that has been knocked out of the K shell during characteristic radiation called?
the ejected orbital electron
What happens after a K shell electron has been knocked out (during characteristic radiation)?
- K shell is now deficient of one electron (unstable)
- an electron from the L shell drops down into the K shell
- the electron from the L shell has too much binding energy so it gets rid of the excess energy as an x-ray photon
- the gap in the L shell then needs to be filled and so an electron from the M shell will fall down into it and so on until we get to the outer shells of the atom
(electrons keep dropping into the shell below until outer shell is reached)
What is the characteristic spectrum characteristic for?
characteristic of the anode atom - in this case Tungsten
What do the line spectra in characteristic radiation relate to?
the K and L shells
What line spectra are of diagnostic important (K or L shell), and why?
K lines are of diagnostic important with photon energy levels of 58-69.5kV
L lines have a photon energy less than 10kV and would be absorbed within the x-ray tube by the lead shielding before reaching the patient
What kV does an x-ray tube need to be operating above for characteristic spectrum to be produced?
above 69.5kV
if operating between 60-65kV only Bremsstrahlung radiation will be produced
What 2 types of radiation can the EM spectrum be divided into?
ionising and non-ionising
What is an image receptor?
the item the x-ray image is formed on, could be a film, plate or digital sensor
What is ‘fogging’ caused by?
photons not having enough energy to make a useful interaction with the receptor, this scatter can degrade the image (fogging)
What are the 2 types of image receptors?
film and digital
What are the 2 types of film receptors?
direct action film and indirect action film
What are the 2 types of digital receptors?
solid state sensors and photo-stimulable phosphor (PSP)
What is direct action film, and what is it used for?
Direct action film is an actual piece of film with silver halide crystals which are sensitive to x-rays, and that is wrapped in a packet. You still may come across direct action film in some general dentist practices.
Used for dental intra-oral radiographs.
What is indirect action film, and what is it used for?
Indirect action film is a film inside a cassette which contains intensifying screens. The x-ray photons react with the intensifying screens to produce light photons, which expose the silver halide crystals in film emulsion to produce the image.
Used for extra-oral radiography.
What are the 2 categories of solid state sensors (digital)?
CCD (charged-coupled device) and CMOS (complimentary metal-oxide semiconductor)
How do digital solid state sensors work?
These sensors work by converting light into electrons. The information is then collected by a computer programme and transformed into the image.
How do PSPs work?
Latent mages are produced by the interaction of x-rays with the phosphor layer on the plate, which is then scanned by a laser to produce the image.
What type of image receptors are used in the DDH radiography department?
PSPs (photostimulable phosphor plates)
What has better resolution, solid state or phosphor plates?
solid state
What is better tolerated by patients, solid state or phosphor plates?
phosphor plates (solid state can be bulky)
Describe a PSP (the different sides etc.)
A pale side which has the phosphor coating (e.g. barium fluoride). This is the side on which the image is formed.
The other is side is black and shows the size of the film and the orientation dot. This is the back of the plate.
The plate is then placed in a protective bag before being used. You should be able to the see the black side of the plate through the window of the bag.
What are the stages of using a PSP?
The stable excited state - the imaging plate is placed into the patient’s mouth and the phosphor coating is exposed to x-rays which causes a reaction within the phosphor.
The unstable excited stage - the plate is then dropped into the vista scan unit where it is scanned by a red laser.
The blue light which is then emitted is collected and then converted to an image.
How is the latent image produced in PSPs?
The phosphor layer on the plate is exposed to x-ray photons, this energy is then stored in the electrons of the phosphor crystals - this is known as the latent image
After a latent image has been produced on a PSP, what happens to the plate?
The plate is inserted into the scanner and the phosphor layer is scanned by a red laser which causes the electrons to drop to lower energy levels by emitting blue light.
This light is then detected by a photodetector and sent to a signal digitiser. This is called an Analogue to digital convertor (ADC).
How does an analogue to digital convertor work (ADC)?
The ADC converts the light to a digital signal, which is basically a numerical value assigned to each pixel according to the intensity of the light detected.
Each pixel’s numerical value corresponds to a different shade of grey which forms the image on the monitor - the grey-scale.
After an image is produced, the PSP still has residual trapped energy in the phosphor electrons, how is the plate erased?
The plate is erased by exposing the phosphor to bright light which releases any remaining trapped energy in the phosphor electrons, and the plate is then ready to reuse.
What are the 4 layers of a CCD sensor?
- a front cover
- a scintillator layer (converts x-ray energy to light)
- a silicon wafer (converts the light into an electrical signal)
- a back cover incorporating a cable to carry the signal to a PC.
How does a CCD work?
X-rays hit the scintillator layer, which is either caesium iodide or gadolinium oxysulphide, and the reaction gives off light which hits the photosensitive cells within the silicon wafer - these make up the pixels of the image.
Electrons within each cell (pixel) are released and these form a charge (voltage) which is converted to the image.
Each cell is connected to its neighbour and the signal converted to the image is from lines of neighbouring cells.
Is the back cover incorporating cable to carry signal to PC in every CCD plate?
No, the most recent digital detectors are wireless, so do not have to connect directly to the computer. This makes it easier for the patient and the image appears within seconds.
CMOS are very similar to CCD, what is the only difference?
the photocells are electrically isolated therefore a signal (voltage) is sent from each individual cell (pixel) rather than lines of cells (pixels).
What is one issue with digital images?
No orientation dot, easy to turn image the wrong way etc.
CCD vs CMOS - what are pros and cons of each in comparison (quality, cost, reliability, power used etc.)?
- CCD possibly better quality image but CMOS catching up
- CMOS cheaper to manufacture
- CCD been around longer, possibly more reliable
- CMOS uses less power
CMOS is like a mobile phone camera, whereas CCD is like a high quality digital camera
What are 6 advantages of digital receptors?
- No chemicals
- Faster processing times
- Easy archiving
- Easy image transfer
- Image manipulation
- Dose reduction
What are 6 disadvantages of digital receptors?
- Expensive - damage
- Reduction in resolution due to pixel size
- Archiving - back-up, software issues etc
- Easy image transfer - security
- Image manipulation
- Dose reduction
Why is easy archiving both an advantage and disadvantage?
easy archiving:
+ almost instant access to the image, won’t get lost in transit or misfiled.
- issues accessing the archive? Power cuts, software issues and cyber terrorism could prevent you from seeing your images.
Why is easy image transfer both an advantage and disadvantage?
easy image transfer:
+ can send the image to anyone anywhere in the world, which has great benefits for teaching and also if you require expert diagnosis
- also easy to send an image to the wrong place or person and this would be a breach of patient confidentiality. The information is also open to hacking from external parties.
Why is image manipulation both an advantage and disadvantage?
image manipulation:
+ you can do almost anything you want to the image, make it bigger, shrink it, flip it, darken it, lighten it, write on it.
- you can do so much to an image now it can end up looking nothing like the way it started which could lead to incorrect diagnoses. Can make you lazy and guilty of bad practice, can over rely on your equipment to think for you as it compensates for poor exposure selection.
Why is dose reduction both an advantage and disadvantage?
dose reduction:
+ advances in computer software have allowed exposure factors to be reduced and consequently the need for repeats to be done because a film has been over or under exposed.
- the shorter exposure times afforded by digital systems also means a drop in resolution on the image.
What does an image which is too dark suggest about the exposure?
a high exposure, too much radiation given
What does an image which is too light suggest about the exposure?
a low exposure, not enough radiation given
If an image is flat, with very few shades of grey and little contrast, what does this suggest?
too high an exposure, the high radiation has caused too much light to be produced in each pixel, which means there is little variation in the electrical signals which are converted to form the image.
If there is white mottling on an image what does this suggest?
too low an exposure , not enough radiation has hit the receptor, no reaction to produce light can occur, therefore no signal from that pixel will be produced and the computer cannot guess and make better what is just not there
In dental practice how are images stored?
stored on a local server, but there must be some form of back up e.g. CD, DVD, Remote Hard Drive
What do most NHS hospitals upload images too?
PACS (Picture Archiving and Communication System)
- in NHS Tayside uploaded to local PACS then transferred to national PACS
- virtually impossible to lose an image
- image accessible from anywhere in Scotland
On PACS what do images taken at DDH start with?
T113H
What size do solid state digital receptors come in?
usually only one size - size 2
What are the 2 types of biological effects of radiation?
Deterministic (non stochastic) - those we know WILL occur
Non-deterministic (stochastic ) - those which MAY occur
What is the relationship of radiation dose and deterministic effects?
deterministic effects definitely occur with specific doses, below threshold the effect does not occur
What is the relationship of radiation dose and non-deterministic effects?
occur at random, no threshold dose
What are the 2 types of deterministic effects?
acute and chronic
What are the consequences of acute deterministic effects?
- radiation sickness: 2-10 Sv whole body irradiation, would begin to have symptoms within a few hours
- death: >10Sv whole body irradiation, would usually occur within 24hrs
What are the consequences of chronic deterministic effects?
- hair loss
- cataracts
- sterility
- obliterative endarteritis
Chronic deterministic effects usually less dramatic than acute deterministic effects but can nevertheless cause severe problems to the patient over a long period of time
What are the 2 types of non-deterministic effects?
somatic effects - development of malignancy
genetic effects - congenital abnormality which may include malignancy (for genetic effects to occur, the reproductive organs of the patient would need to be exposed to radiation)
Which type of effects are we likely to have in dentistry?
non-deterministic
What factors affect dose of radiation?
- type of radiation - we are interested only in x-rays
- tissues being irradiated - different tissues may have different sensitivities to radiation
- age of the patient - younger patients generally more susceptible to changes within their tissues than older patients
What are the dose limits per annum for classified workers, non-classified workers, and the general public?
classified worker - 20mSv
non-classified worker - 6mSv
general public - 1 mSv
What dose limit per annum should dentists try to comply with?
general public - 1mSv
What does ALARP stand for?
As
Low
As
Reasonably
Practicable
patients should only be exposed to radiation if it’s clinically necessary
What is the correlation of age and risk of developing adverse effects from radiation?
The younger the patient is, the greater the risk of developing adverse effects form radiation
What are some practical means of dose reduction?
- avoid unnecessary radiographs
- use of selection criteria
- film speed - preferable use F speed (highest speed possible)
- kV of machine - higher the kV, lower the dose
- rectangular collimation
- collimated DPT views
- regular servicing of machines
- knowledge and understanding
What is the importance of intensity and the inverse square law?
Photons get spread over a bigger area the further they are
This change in the intensity of the radiation is applied to the inverse square law
Intensity of radiation is proportional to one/distance squared
The further we are from the source of radiation, the less likely we are to be exposed to many x-ray photons
What is the diameter of the control area in a machine working at <70kV?
1.5m
BUT size depends in local rules, DDH stand 2m away for all machines or behind appropriate shielding
What are the 4 layers of a direct action film packet?
- outer plastic wrapping
- black paper
- lead foil
- film
What is the purpose of the outer plastic wrapping in a direct action film packet?
- keeps film dry - saliva free
- protects film from light damage - fogging
- indicated the correct orientation of the film in the mouth - white side towards x-ray tube,bump places at crown of tooth
What is the purpose of the black paper in a direct action film packet?
- protect film from light leakage
- helps prevent crimp and pressure marks on the film by providing support
What is the purpose of the lead foil in a direct action film packet?
- mixture of lead and aluminium
- readily absorbs x-rays
- prevents back scatter
- has a distinct pattern embossed into the lead, will see this on the image if film placed back-to-front
What are the features of the film in a direct action film packet?
- base - plastic (polyester or cellulose)
- anti-glare tine - blue
- adhesive layer
- double emulsion
- protection layer of gelatin
What is the emulsion layer in a direct action film for?
The emulsion is the layer that reacts with the x-rays to form the image. It is comprised of silver halide crystals, usually silver bromide, suspended in gelatin.
The gelatin performs 2 functions- it allows even distribution of the crystals and it also absorbs liquid easily which helps during processing.
What is the purpose of the adhesive in direct action film?
sticks the emulsion to the base layer and the super coat helps protect the emulsion from physical damage
How is a latent image formed on direct action film?
x-ray photons hits silver halide crystal within emulsion of film, the silver halide crystal then becomes sensitised to produce the latent image
Describe the correlation between film speed, crystal size, and the image produced
larger crystals = faster film speed = lower resolution image (less detail)
What are indirect films sensitive too?
primarily to light - not x-rays
How do indirect films work?
The x-rays react with the intensifying screens to produce light which then exposes the film.
The light produced is in direct proportion to the x-rays that hit the screens.
This system allows you to reduce the exposure required to produce an image and therefore the dose received by the patient.
What are the layers of an intensifying screen? (indirection action film)
- base - plastic or polyester
- reflective layer - reflects all the light produced back towards the film
- phosphor layer - reacts with x-rays to produce the light (the light produced is in direct proportion to the energy in the x-ray photon)
- supercoat - protects the phosphor layer from damage
How do intensifying screens allow a significant reduction in the radiation exposure to the patient?
the screen in front absorbs and converts the low energy photons to light and the screen at the back absorbs the high energy photon and converts them to light, making the system extremely efficient.
How does the use of indirect action film effect image quality?
reduces detail seen in the image due to one x-ray photon producing several light photons, in-turn exposing large area of the film
What are the key points about how/where film should be stored?
- cool - not too hot, not too cold
- dry - but not too dry
- away from radiation - x-rays, heat
- if box is opened, store in darkened conditions (e.g. hopper)
- stock rotate to ensure not using old/out-of-date film
What does ‘film processing’ describe?
the reduction of the exposed silver bromide crystals to black metallic silver and then making this image permanent
What are the 3 methods of film processing?
- automatic
- manual
- instant
What are the 5 stages of film processing?
- develop - make latent image visible
- wash - stop development and remove dev from film (only in manual processing)
- fix - make image permanent
- wash - stop fix and remove residual fixer
- dry - easier handled, prevent damage
How does an automatic processor work?
film over between tanks by rollers, the journey through each tank takes the exact amount of time required for the chemical reactions to take place
What does the ‘developing’ stage of film processing involve?
Placing the film in a tank of developer allows the developing agents phenidone and hydroquinone to act upon the sensitised silver halide crystals.
This causes the chemical reduction of the silver bromide to silver plus bromide.
The silver is in the form of black metallic silver, which gives the blackening you can see on the film.
What are the components of developer in film processing?
- developing agents - phenidone and hydroquinone
- activator - calcium carbonate (controls the activity of the developing agents)
- restrainer - potassium bromide (stops developer working on unexposed crystals)
- preservative - sodium sulphite (slows down oxidation)
- solvent - water
each developer has its own optimum working temperature
What 3 things is the action of the developing agents on the silver halide crystals dependant on?
- time: too long- dark, too short- light
- temperature: too hot- dark, too cold- light
- concentration: too strong- dark, too weak- light
What does the ‘fixing’ stage of film processing involve?
the fixing agents change unexposed silver halide to soluble compound so they can be washed away
acid maintains the pH and neutralise the developer
What are the 5 components of fixer?
- Clearing agent - ammonium thiosulphate
- Acidifier - acetic acid (maintains pH)
- Hardener - aluminium chloride
- Preservative - sodium sulphite
- Solvent - water
What happens to silver halide crystals during fixing?
unexposed silver halide crystals are removed during the fixing process
left with the silver halide crystals which have been developed and fixed
What happens to an image that is under-fixed?
will appear to have a green tinge, won’t archive well -will degrade over time until it is undiagnostic
What is the purpose of washing in both manual and automatic film processing?
to remove unexposed silver halide crystals once made soluble by fixer
In manual film processes, there is an additional ‘wash’ step, when is this and what is it’s purpose?
between developing and fixing, as well as between fixing and drying (as in automatic)
stops action of developer and reduces carryover
What are the effects of insufficient washing?
- film will feel tacky
- may also have a green or silvered appearance (cloudy)
- will not archive well - image will deteriorate
What is the purpose of drying during film processing?
- ensures the film is dry before it is handled
- reduces the possibility of damage to emulsion
When is instant film processing beneficial?
if you have to process images away from a power source
In health and safety, what does COSHH stand for?
control of substances hazardous to health
How much ventilation should a film processing room have?
adequate ventilation - 10 or more room volumes per hour
How often must the chemicals in a film processor be changed, and the processor stripped and cleaned?
every 2 weeks
In bitewing radiography, what happens to the image when their is an upward angulation of the x-ray beam?
elongation
In bitewing radiography, what happens to the image when their is an downward angulation of the x-ray beam?
fore-shortening
Why are bitewings taken?
- detect caries
- monitor caries progression
- assess periodontal status
- assess existing restorations
What teeth should horizontal bitewing radiographs show?
distal 4 to mesial 8
What teeth should vertical bitewing radiographs show?
pre-molars and molars
How much of the teeth do horizontal bitewing radiographs show?
crowns and 1/3 roots
How much of the teeth do vertical bitewing radiographs show?
more of the roots than horizontal bitewings
When would you take a vertical bitewing over a horizontal bitewing?
when you need to see more of the root and supporting bone during a perio assessment
For a bitewing radiograph, there is a notch in the middle of the bite block. Where should you place this to be in the right position?
the centre of the 6 (1st molar)
What are the 3 positioning requirements for a bitewing radiograph?
- film and object parallel
- film close to object
- x-ray beam perpendicular to object and film
What colour holder for a bitewing?
red
What are the 2 holder types for a bitewing, and what are their main pros and cons?
rigid plastic
- holds film accurately
- assists x-ray tube positioning
- uncomfortable
paper tab
- comfortable
- x-ray tube positioned by eye
- inaccurate positioning
What happens if the film and x-ray rube are not parallel in the horizontal plane?
images with overlap of the teeth, could lead to missing early carious lesions
What happens if the receptor and x-ray tube aren’t parallel in the vertical plane?
bone levels projected off the receptor, and distortion of teeth leading to separation of the cusps
Where should the dot on a bitewing radiograph go?
dot to the palate
What 3 things can reduce human error?
- simple systems, SOPs
- improve working environment
- encourage reporting - without blame
What 2 laws are in place surrounding radiography in the UK, and who do they protect ?
- IR(ME)R 2017 - protects the patient
- IRR 2017 - protect staff and public but also deals with patient protection in relation to equipment
What are the 4 roles outlined in IR(ME)R 2017?
- employer - the boss
- practitioner - justification
- operator - anyone involved in the production of a radiograph
- referrer - one who refers the patient for radiographs
dentists are quite unique - can be every one of these roles
How much CPD specific to radiation safety does every practitioner and operator involved in dental radiography need?
5 hours every 5 years
What does a Quality Assurance Programme include?
- named person - in charge of overseeing compliance, normally the practice RPS
- details of procedures involved
- frequency procedures carried out
- frequency records will be audited
- all the above must be put in writing
What is looked at in a QA programme?
- image quality
- x-ray equipment
- processing (film and digital)
- working procedures
- training
- audit
What percentage of radiographs should you be aiming to be rated Acceptable (for digital system and for film)?
more than 95% rated A if using a digital system
more than 90% rated A if using film
As well as keeping a record of the number of N rated radiographs taken, what else about them should be recorded?
reason the image was rejected
During QA, what are some categories considered during reject analysis?
was the image rejected due to:
- poor exposure factors
- an error in positioning
- a processing fault
- did the patient move?
- operator error?
- equipment fault?
How often does x-ray equipment needed to be tested?
preferably annually but minimum of every 3 years
During QA, how is the radiation output from x-ray units checked?
by carrying out a series of exposures over a dosemeter which tells you an exact measurement of equivalent dose
How is QA of processing (film and digital) done?
- storage and stock rotation
- monitoring of processor performance
- processor maintenance
- monitoring performance of digital system
How should PSP receptors be stored?
- cool and not too humid
- avoid direct sunlight and UV
- preferably in light protection/cross infection barrier envelope
- if not used for more than 24hrs after plate erased (exposure to bright light) it should be erased again
What does sensitometry compare?
compares film processed wit fresh chemistry with images produced as developer gets exhausted
What does exhausted developer cause
exhausted developer = pale image
What are the steps of checking sensitometry?
- make a simple step-wedge (a radiographic phantom made from differing thicknesses of metal)
- place step-wedge on dental film packet and expose
- process film in fresh chemistry
- expose a step wedge film daily
- check films for obvious change in densities e.g. drop of one step from standard reference film
What are the differences between step wedge films vs pre-exposed test film?
step wedge:
- cheap - uses intra-oral film
- operator variables can cause discrepancies in production
- results variable depending on viewer
pre-exposed:
- expensive
- easy to use
- no discrepancies in production - every film should be the same
- results not dependant on viewer
What are some common problems during film problems during film processing caused by?
damage due to:
- poor handling - bends, crimps
- insufficient training - overlapped
- light - fogging
What test do you carry out to test film for fogging?
the coin test
How do you carry out the coin test?
- open an intra-oral c-ray packet and remove film - while hands are inside glove box or in darkroom under safelight conditions
- place a coin on the film
- leave coin on film for a specified amount of time (5 mins or avg. working time)
- remove coin and process film
- check and processed film for light fogging
- repeat test for every different type and speed of film used in the practice
- act on your findings
On a radiograph, what can be mistaken for caries?
- cervical burnout or translucency
- visual perception - problem of contrast below dense metallic restoration
- air/lip shadow in premolar region
- dentine surrounding radio-opaque zone under amalgam
- radio lucena restorations
How often should bitewing radiographs be taken in children (caries risk assessment)?
high risk child - 6 monthly
moderate risk child - annually
low risk child - 12-18 monthly for deciduous teeth, 24 months or more for permanent teeth
What is the trabecula pattern like in the mandible, and in the maxilla?
mandible - thick, close together, horizontally aligned
maxilla - finer, more widely spaced, no obvious alignment pattern
What are the 3 most important features in radiology and peri-radicular disease?
- radiolucent line representing the periodontal ligament space
- radiopaque line representing lamina dura
- trabecula pattern and density of surrounding bone
What is the radiographic appearance of initial acute inflammation?
no apparent changes, or possible widening of periodontal ligament space
What is the radiographic appearance of initial spread of inflammation?
loss of lamina dura at apex
What is the radiographic appearance of further inflammatory spread?
periapical bone loss
What is the radiographic appearance of initial chronic inflammation?
no bone destruction seen, or dense sclerotic bone periapically (sclerosing osteitis)
What is the radiographic appearance of chronic inflammation - long standing?
circumscribed, well defined, radiolucent area periapically with sclerotic bone surrounding
radiolucency sometimes described as rarefying osteitis
What are the 3 positioning landmarks?
- radiographic base line
- frankfort plane
- maxillary occlusal plane
Describe the radiographic base line
line from outer canthus of eye to EAM (ext. auditory meatus) - represents base of skull
Describe the frankfort plane
IOB (inf. orbital border) to upper border EAM (ext. auditory meatus) - also known as the anthropological base line
Describe the maxillary occlusal plane
ala of most to tragus of ear
What landmark is used when taking a DPT?
frankfort plane
What positioning landmark is used often in cone beam CT?
maxillary occlusal plane
What is scatter radiation?
This is when weaker x-ray photons are deviated off track as they do not possess enough radiation to pass all the way through to the receptor and make a useful interaction.
What does scatter cause on the image?
fog
What does an anti-scatter grid do?
- stops photons scattered in patient reaching the film
- avoids degrading image and reducing contrast
What is an anti-scatter grid made of?
narrow strips of lead alternating with plastic
- can be either fixed/stationary or moving/oscillating
What are the indications for a PA mandible radiograph?
- fractures - show medio-lateral displacement
- cysts and malignancy causing medio-lateral expansion or bone destruction
- good visualisation of posterior body and ramus
however: - limited visualisation of head/neck of condyle
- midline can be obscured by spine
requested along with a DPT
What external landmarks are used to find the mid-line of a patient?
front: generally between the eyes
back: external occipital protuberance
Why do we take an oblique view of the mandible instead of a lateral view?
if it was truly lateral, the 2 halves of the mandible will be superimposed and as the x-rays pass through both rami you will see both on the final image. The superimposition will make it difficult to make sense of anything that you can see.
What are some possible indications for an oblique mandibular radiograph?
- fracture of body, ramus and condyle
- pathology e.g. cysts
- assessment of wisdom teeth (DPT would be requested first)
- dental assessment in special needs patients
- caries in children (who can’t tolerate bitewings)
Describe isocentric positioning of a patient
- patient supine
- position patient for area to be imaged
- rotate machine into the horizontal plane
- angle 25 degrees towards the head
- tilt top of patients head towards the film
Describe vertical angulation (for oblique mandibular radiographs)
- patient holds cassette against and parallel to the are a under examination
- tube head is positioned beneath the lower border of the body of the mandible that is not under examination
- aim the tube towards the teeth under investigation
- angle the tube head slightly upwards
- this view will project the opposing body of mandible up and therefore away from the area of interest
Describe horizontal angulation (for oblique mandibular radiographs)
- patient holds cassette against and parallel to te area under examination
- tubehead is positioned aiming along the occlusal plane just below the ear towards the maxillary and mandibular teeth that are the be examined
- this aims through the radiographic keyhole which is the triangular space between the back of the ramus and the cervical spine
