6 Image Receptors (2) Flashcards
Radiographic Film Receptors and processing
what is direct action film used for?
intra-oral radiographs
- peri-apical
- bitewing
- occlusal
what are the 4 layers on a direct action film packet?
- outer layer of plastic wrapping
- black paper
- lead foil
- direct action film
what is the purpose of the outer layer of plastic wrapping in a direct action film packet?
- completely sealed to keep film dry, light tight (to prevent fogging)
What side of the direct action film do you want to face the x-ray tube?
the white side, which has a raised bump which should be placed at the crown of the tooth
what is the purpose of the black paper layer in a direct action film packet?
- this helps prevent the film from light leakage
- also helps prevent crimp and pressure marks on the film by providing a bit of support
what is the purpose of the lead foil layer in a direct action film packet?
Lead foil absorbs back scatter
- when powerful x-rays pass through the tooth and hit other structures (e.g. the tongue), irradiating areas which are not required. These photons may then bounce back towards the film (back scatter) and would degrade the image if left unchecked
what are the 4 basic components of radiographic film?
- a base layer (polyester plastic)
- an adhesive layer
- emulsion layers
- protective layer of gelatine (super coat)
what is the emulsion layer of radiographic film comprised of?
- silver halide crystals (usually silver bromide)
- suspended in gelatine
What are the 2 functions of the gelatine in the emulsion layer of radiographic film?
- allows even distribution of the crystals
- absorbs liquid easily which helps during processing
How is the image formed on a radiographic (direct) film?
The x-ray photons sensitise the silver halide crystals that they strike and these senstised silver halide crystals are later reduced to visible black metallic silver in the developer
- the sensitised crystals form the latent image
what is the latent image?
an invisible image that appears on film after being exposed to light or radiation, but before it has been chemically processed.
It is the pattern produced within the emulsion by the sensitising of silver bromide crystals (by light or x-rays)
X-ray film is available in 2 speeds (fast and slow), what is this dependant on?
The speed of the film is the sensitivity of the film to x-rays (how big an exposure is required to produce a certain degree of blackening on an image)
What is the sensitivity of the film dependant on?
The sensitivity of the film is dependant on the size of the crystals in the emulsion
(the larger the crystal the faster the film speed and the lower the amount of x-rays required to produce an image)
- however, the larger the crystals, the less detail you have on the film
What are the most common film sizes?
0, 1, 2, 4
(used for same as digital receptors)
0, 1 - periapical anteriors (adult) and full dentition children
1, 2- adult posteriors or anteriors and bitewings
4 - occlusals
What is indirect film used for?
Extra-oral radiographs
- DPTs
- Lateral cephs
- Other head and neck radiographs
Rare to see now
How is indirect film different from direct film?
Indirect film is sensitive to light rather than x-rays
How does indirect film reduce dose received by the patient?
The x-rays react with the intensifying screens to produce light which then exposes the film.
This reduced the exposure required to produce an image as the screen in front absorbs and converts the low energy photons to light and the screen at the back absorbs high energy photons and converts them to light
The light produced is in direct proportion to the x-rays that hit the screens, true or false?
True
What are the different layers of the intensifying screen of an indirect film?
- base layer (plastic/polyester)
- reflective layer (reflects all the light produced back towards the film)
- phosphor layer (reacts with x-rays to produce the light)
- super coat - protects the phosphor layer from damage
what leads to reduction in fine detail in indirect film?
One x-ray photon will produce several light photons, which in turn exposure large areas of film, which leads to reduction in fine detail
How can pressure damage a radiographic film?
pressure sensitises the silver halide crystals
For intra-oral films, what are the 3 methods of processing?
- automatic processor
- manual processor
- instant processor
what are the basics of an automatic processor?
you place the film between 2 rollers which would then feed the film through the tanks and it pops out developed
what are the basics of a manual processor?
you are responsible for placing the film into the various tanks of chemicals until the image is ready. This means that you have to keep a close eye on the time the film is spent in each tank
What are the basics of instant developing
The chemicals contain bubbles in the pouch which burst and slide around the film
- only tends to be done in disaster situation as it is not very reliable
What are the 5 stages to developing and image?
Develop - where you make the latent image visible
Wash (the first wash only happens in manual processors)
Fix - where you make the image permanent
Wash - stop the fix and remove the residual fixer
Dry - stops the image feeling sticky and prevents damage
What are the 2 developing agents which reduce silver bromide to silver plus bromide
phenidone and hydroquinone
in the developer, what is the activator?
calcium carbonate (controls the activity of the developing agents)
in the developer, what is the restrainer?
potassium bromide (stops the developer working on unexposed crystals)
in the developer, what is the preservative?
sodium sulphite - slows down oxidation
what does the fixing agent do to the image?
changes unexposed silver halide to soluble compound so they can be washed away
in the fixer, what is the clearing agent?
ammonium thiosulphate
in the fixer, what is the acidifier?
acetic acid (maintains pH)
in the fixer, what is the hardener?
aluminium chloride
in the fixer, what is the preservative?
sodium sulphite
how will an under fixed image appear?
green tinge and will not archive well
what is the effect of insufficient washing?
film will feel tacky
may have a green or silvered appearance
will not archive well - will deteriorate
The health and safety at work act 1974 resulted in what legislations being formed?
COSHH (control of substances hazardous to health) regulations
Manual handling at work - risk assessment
what is the potential health effect of the chemical constitute acetic acid?
skin senstation
what is the potential health effect of the chemical constitute gluteraldehyde?
allergic contact dermatitis
what is the potential health effect of the chemical constitute hydroquinone?
occupational asthma
what is the potential health effect of the chemical constitute potassium hydroxide?
persistant cough
what is the potential health effect of the chemical constitute sodium sulphite?
COPD
what is the potential health effect of the chemical constitute phenidone?
possible carcinogen
what is the potential health effect of the chemical constitute aluminium sulphate?
headaches
