Image receptors 2 Flashcards
Why is there an outer plastic wrapping on films?
Keeps film dry – saliva free.
Protects film from light damage – fogging.
Indicates the correct orientation of the film in the mouth – white side towards x‐ray tube
Why is there black paper in the film packet?
Protect film from light leakage
Stiffens & supports film. This is to prevent crimp/pressure marks on the film
Why is there lead foil in the film packet?
- Composed of a mixture of lead and aluminium .
- Readily absorbs x‐rays.
- Prevents back scatter.
- Has a distinct pattern embossed into lead.
What does the flim have?
- Direct action.
- Base ‐ plastic (polyester or cellulose)
- Anti‐glare tint – blue
- Adhesive layer
- Double emulsion
- Protective layer of gelatin.
What are the layers of a dental Film?
What is the Emulsion layer?
- Silver halide crystals suspended in gelatin.
- Silver bromide, silver iodide or a combination of the two.
- Gelatin allows even distribution of crystals.
- Gelatin absorbs liquid readily to allow processing.
- Adhesive layer “sticks” the emulsion to the base.
- Super coat – an additional protective layer of gelatin.
How is the image formed?
- Direct action (intra‐oral)
- X‐ray photon hits Silver Halide crystal within emulsion of film
- Silver halide crystal becomes sensitized
- Latent Image
What is a Latent Image?
It is the pattern produced within the emulsion by the sensitizing of silver bromide/iodide crystals, either by light or x-rays.
It is not visible to the naked eye but can be made so by the chemical reactions that take place during processing.
The main reaction being the reduction of the silver bromide crystals to black metallic silver
What is the film speed dependent on?
- Dependent on the size of crystals in the emulsion.
- Larger the crystals the faster the film speed.
- Faster the film speed the lower the amount of x‐rays required to produce an image.
- Larger crystals = reduced detail
What is a Direct action film and an Indirect action film?
Direct Action Film (Intra‐oral)
Indirect Action Film (Extra‐oral)
What is an Indirect Film?
- Indirect film
- Sensitive primarily to light
- Light produced by intensifying screens inside the cassette.
- The light produced is in direct proportion to the x‐rays that hit the screens.
- Reduces exposure required to produce image and therefore the dose received by patient
What is a Intensifying Screen?
- Base – polyester.
- Reflective layer.
- Phosphor layer ‐ fluorescent phosphors, emit light when excited by x‐rays. T
- he light produced is in direct proportion to the energy in the x‐ray photon.
- Supercoat – protects phosphor layer from damage
Allow a reduction in exposure and therefore a reduced dose to patient BUT Reduction in detail in image
How is an image formed in Indirect Action?
Indirect action (extra‐oral)
- X‐ray photon hits phosphor crystal in intensifying screen.
- Gives off light.
- Light hits Silver Halide crystal within film emulsion.
- Silver halide crystal becomes sensitized.
- Latent Image
Where do you store film?
Cool – not too cool
Dry – not too dry
Away from radiation – x‐rays, heat.
Stock rotation to prevent using old film
What are the 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 the film Develop?
- Sensitized silver halide crystals (silver bromide/iodide) are acted on by the developing agents phenidone and hydroquinone which involves the chemical reduction of silver bromide to silver plus bromide
- Silver is in the form of black metallic silver
- Thus giving the blackening on the film
What is in the Developer?
(Developing agents, activator, restrainer, preservative and solvent)
Developing agents ‐ Phenidone & 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
What is The action of the developing agents on the silver halide crystals is very dependant on?
- Time: Too long ‐ dark. Too short ‐ light.
- Temperature: Too hot ‐ dark. Too cold ‐ light.
- Concentration: Too strong ‐ dark. Too weak ‐ light
What is film processing?
THE REDUCTION OF THE EXPOSED SILVER BROMIDE CRYSTALS TO BLACK METALLIC SILVER AND THEN MAKING THIS IMAGE PERMANENT
What is the Developer?
making the image visible
What is the fixer?
Making the image pernament
What does the fixing agents do and what is in a Fixer?
- The fixing agents change unexposed silver halide to soluble compound so they can be washed away.*
- Acid maintains the pH and neutralize the developer.*
Clearing agent ‐ Ammonium thiosulphate
Acidifier ‐ Acetic acid (maintains pH)
Hardener‐ Aluminium chloride
Preservative ‐ Sodium sulphite
Solvent ‐ Water
What is The action of the fixing agents on the silver halide crystals is very dependant on?
Time, temp, concentration?
Not as critical as developer but if over fixed image will be removed from film.
Under fixed will appear to have green tinge and will not archive well.
When do you wash?
Manual ‐ between dev and fix and between fix and dry.
Stops action of developer and reduces carryover
Remove unexposed silver halide crystals once made soluble by fixer
Automatic ‐ only between fix and dry
Remove unexposed silver halide crystals once made soluble by fixer
What are the different methods of film processing?
AUTOMATIC
- Consistent
- Less operator dependant
- Temperature controlled
- Time controlled
- Less chance to damage film
MANUAL
- Very operator dependant
- Done well can be as good as automatic.
- Temp must be monitored
- Time must be accurate
INSTANT
- Chemicals in pouch attached to film
- Very quick
- No large amount of chemicals to be disposed of
- Convenient
- Films do not archive well
What does COSHH stand for in health and safety?
CONTROL OF SUBSTANCES HAZARDOUS TO HEALTH
What is the adequate ventilation for recommended handling?
Adequate ventilation ‐ 10 or more room volumes per hour
