Image Receptors 2 Flashcards
What is the purpose of the barrier wrapped film?
Outer plastic wrapping?
Barrier wrapped film:
- good infection control and protects film from saliva
- torn open on completion of x-ray and disposed of in clinical waste, leaving clean film packet ready to handle
Outer plastic wrapping:
- completely sealed to keep film dry from saliva
- keeps film light tight to prevent fogging
- completely white side faces x-ray source
- raised bump on white side –> placed at crown of tooth
What is the purpose of the black paper?
Lead foil?
What are the layers of direct action film?
Black paper:
- prevent from light leakage
- stiffens and supports film to prevent crimp and pressure marks
Lead foil:
- composed of a mixture of lead and aluminium
- readily absorbs x-rays, prevents back scatter
- has a distinct pattern embossed into lead
Direct action film:
- polyester base layer, anti-glare tint, emulsion protected by a layer of gelatine
What is film emulsion?
What is the purpose of gelatine?
Adhesive layer?
Emulsion - layer which reacts with the x-rays to form the image, comprised of silver halide crystals suspended in gelatine
Gelatine: allows even distribution of crystals and it absorbs liquid easily which helps during processing
Adhesive layer: sticks the emulsion to the base layer and the supercoat helps protect the emulsion from physical damage
What is the latent image?
Latent image:
- pattern priduced by emulsion by the sensitising of silver bromide crystals, either by light or x-rays
- not visible to the naked eye but can be made visible during processing
- main reaction being the reduction of the silver bromide crystals to black metallic silver
What is film speed?
What is it dependent on?
Film speed: sensitivity of the film to x-rays (how big an exposure is required to produce a certain degree of blackening on an image)
- dependent on size of crystals in the emulsion - the larger the crystals, the faster the film speed and the lower the amount of x-rays required to produce an image
- but the larger the crystals, the less detail you have on the image (lower resolution)
What can a size 0 film be used for?
1?
2?
4?
0 - anteriors and children (deciduous teeth)
1 - canines
2 - posteriors and BW for children over 10
4 - occlusals
What is an indirect action film?
- sensitive to light rather than x-rays
- x-rays react with intensifying screens to produce light which exposes film
- light produced in direct proportion to x-rays that hit the screens
- allows reduction in exposure required to produce an image and reduced dose to patient
What are the layers of an intensifying screen?
- base layer - plastic or polyester
- reflective layer - reflects all the light produced back towards the film
- phosphor layer - reacts with x-rays to produce light, the light being produced being in direct proportion to the energy in the x-ray photon
- supercoat - layer of gelatine to protect the phosphor layer from damage
Why is the use of intensifying screens beneficial?
Are there any downsides?
- allows significant reduction in radiation exposure as the screen infront absorbs and converts low energy photons to light and the screen at the back absorbs the high energy photons and converts them to light, making the system extremely efficient
- reduction in detail of image
How is an image formed using intensifying screens?
- x-ray photon hits phosphor crystal in intensifying screen
- gives off light
- light hits silver halide crystal within film emulsion
- silver halide crystals become sensitised –> latent image
Define film processing:
What are the methods for film processing?
Film processing: the reduction of the exposed silver bromide crystals to black, metallic silver and then making this image permanent
Methods of film processing:
- automatic
- manual
- instant
What are the stages of processing?
- Develop: make latent image visible
- Wash: stop development and remove excess developer (only in manual)
- Fix: where you make image permanent
- Wash: stop the fix and remove residual layer
- Dry: stops the image feeling sticky and prevents damage
What is in the developer?
- 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 sulphate slows down oxidation
- solvent: water dilutes chemicals
The action of the developing agents on the silver halide crystals is dependent upon what?
- time: too long = dark, too short = too light
- temperature: too hot = dark, too cold = light
- concentration: too strong = dark, too weak = light
What is fixing?
What is removed during fixing?
What components make up the fixer?
Fixing - making image permanent
Unexposed silver halide crystals are removed during fixing
- fixing agents change unexposed silver halide ions to soluble compound so they can be washed away
- clearing agent: ammonium thiosulphate
- acidifier: acetic acid maintains pH
- hardner: aluminium chloride
- preservative: sodium sulphate
- solvent: water
