6 - Image Receptors 2 Flashcards
barrier wrapped film: what does the barrier provide?
infection control
outer plastic wrapping: 3 uses?
- keeps film dry & saliva free
- protects film from light damage: fogging
- indicates the correct orientation of the film i the mouth: white side towards xray tube
black paper: uses?
- protect film from light leakage
- stiffens and supports film, to prevent crimp/pressure marks on the film
lead foil: composed of? uses?
- composed of a mixture of lead and aluminium (has distinct pattern embossed into lead)
- readily absorbs xrays
- prevents back scatter
film: what are the 5 layers?
- base: plastic (polyester), blue anti glare tint
- 2 adhesive layers
- double emulsion layers
- protective layer of gelatine
emulsion: what is suspended in the gelatin? what is it made of? what does the gelatin allow? adhesive layer: what does it stick? supercoat: consists of?
- silver halide crystals; made of silver bromide, silver iodide or both
- allows even distribution of crystals
- gelatin absorbs liquid readily to allow processing
- sticks emulsion to the base
- consists of a protective layer of gelatin
image formation: on direct action (intra oral film) - how is latent image produced?
x-ray photon hits silver halide crystals within emulsion of film
silver halide crystal becomes sensitised, thereby producing the latent image
what is the latent image?
how is it made visible to the naked eye?
what is the main reaction?
- the pattern produced within the emulsion by the sensitizing of silver bromide/iodide crystals, either by light or xrays
- done by chemical reactions that take place during image processing
- the reduction of silver bromide crystals to black metallic silver
what is film speed?
what does it mean when the film is “fast”?
- the exposure required to produce a given amount of blackening (optical density) on an image
- it means that less exposure is required for a given film blackening and therefore lower radiation dose to the patient
film speed:
dependent on?
what is compromised with fast film speed?
- film speed is dependent on the size of crystals in the emulsion.
- larger crystals, faster speed
- larger crystals mean faster speed, but also reduced detail in the x-ray
indirect film: sensitive to? light produced by? relationship between light produced and x-rays that hit the screen? how is exposure affected?
- sensitive primarily to light
- light produced by intensifying screens inside the cassette
- more light produced, more x-rays hit the screens
- amount of radiation required to expose the film is reduced, meaning that exposure is reduced.
intensifying screen - layers? what is each made of?
- base: polyester
- reflective layer
- phosphor layer: fluorescent phosphors, emit light when excited by x-rays
- supercoat: protects phosphor layer from damage
radiographic film susceptible to damage by? how is the damage specifically done?
- pressure marks - crimp/bend marks
- pressure sensitises the silver halide crystals
best ways to handle film and prevent damage?
handle film with care:
- hold by corners/sides
- beware of leaving fingerprints on image
- wet or dry emulsion easily scratched
- support extraoral film when feeding into processor
film storage: ideal conditions?
- cool; not too cool
- dry; not too dry
- away from radiation: xrays, heat
- stock rotation to prevent using old film
image formation: direct action?
- xray photon hits silver halide crystals within emulsion of film
- silver halide crystal becomes sensitised
- latent image produced
image formation: indirect action?
- xray photon hits phosphor crystal
- gives off light
- light hits silver halide crystals within film emulsion
- silver halide crystals sensitized
- latent image produced
processing of image - FILM:
what are the 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 developer from film (manual only)
- fix: make image permanent
- wash: stop fix and remove residual fixer
- dry: easier handled, prevent damage
components of automatic image processor?
- feed in rollers
- developer rack
- fixer rack
- wash rack
- dryer
developing:
sensitised silver halide crystals are acted on by what substances in the developing agent?
what is the chemical reaction involved?
how is blackening on the film achieved?
- silver crystals are acted upon by phenidone and hydroquinone
- silver bromide undergoes reduction into silver plus bromide
- silver is in the form of black metallic silver; therefore producing blackening
developer: developing agents? activator + function? restrainer + function? preservative + function? solvent?
- phenidone and hydroquinone
- calcium carbonate. it controls the activity of the developing agents
- potassium bromide. it stops developer from working on unexposed crystals
- sodium sulphite. it slows down oxidation
- water
action of developing agents on silver halide crystals is dependent on?
- time: if too long, image will be dark. if short, image will be light.
- temperature: too hot, image too dark. too cold, image too light
- concentration: too strong - dark. too weak, image too light
fixing: what do the fixing agents do?
- change unexposed silver halide to soluble compound so they can be washed away (wash stage)
- acid maintains the pH and neutralizes the developer
fixer: clearing agent? acidifier + function? hardener? preservative? solvent?
- ammonium thiosulphate
- acetic acid (maintain pH)
- aluminium chloride
- sodium sulphite
- water
action of fixing agents on silver halide crystal is dependent on?
how is it different from the developing stage?
what happens when image is over or under fixed?
- time, temperature, concentration
- not as critical as developing stage
- over fixed: image will be removed from film
- under fixed: image will have green tinge and will not archive well
wash: when to carry out for the manual process?
what does it do? x2
- between development & fix,
- between fix & dry stages
- stops action of developer, reduces carryover
- remove unexposed silver halide crystals once made soluble by fixer
wash: when to carry out for automatic stage?
what is the purpose?
- only between fix & dry
- washes away unexposed silver halide crystals made soluble by the fixer
wash: what happens when wash is insufficient?
- film will feel tacky
- will/may also have a green or silvered appearance
- will not archive well, image will deteriorate
drying: why should image be dried well
- reduce possibility of damage to emulsion
automatic processing: advantages? x5
- consistent
- less operator dependent
- temperature controlled
- time controlled
- less chance to damage film
manual processing: advantage?
disadvantages? x3
- if done well can be as good as automatic
- very operator dependent
- temp must be monitored
- time must be accurate
instant processing: 4 advantages and 1 disadvantage?
- chemicals in pouch attached to film
- no large amount of chemicals to dispose of
- very quick
- convenient
- films do not archive well
what are the 3 steps to correct processing?
- develop correct density of image: not too dark or light
- fix & wash: for good archiving
- dry: so film is undamaged
health & safety: what does COSHH stand for?
control of substances hazardous to health
manufacturers must provide what for potentially hazardous substances?
Material Safety Data Sheet
developer: how harmful? possible risk of? skin contact causes?
inhalation?
- limited evidence of carcinogenic effect
- irreversible effects
- may cause sensitization
- inhalation considered low hazard
fixer: harmful? what to beware of? releases what potentially harmful substances upon contact with strong acid or alkali?
- not hazardous
- is corrosive
- can release sulphur dioxide or ammonia on contact with strong acid/alkali, potentially harmful
recommended handling for image processing agents?
- adequate ventilation: 10 or more room volumes per hour
- PPE: googles, respirator, apron and gloves both chemical resistant
