4. DEFINITION
Processing is a collective title given to a series of
operations carried out in the dark room, which effect
chemical
changes
in
the
exposed
radiographic
film, making the invisible latent image, contained in the
sensitized film emulsion into a visible, permanent
radiographic image
5. LATENT IMAGE
A radiographic film is a recording medium used in dental
radiography.
When
this
film
is
exposed to the
information carrying beam of photons exiting an
object, the photosensitive silver halide crystals in the
film emulsion interact with these photons and are
chemically changed. These chemically altered crystals
are said to constitute the latent (invisible) image of
the film
6.
These chemical changes in the crystals increase the
liability of crystals to chemical action of the developing
process that converts the latent image into manifest
(visible) image
7. FORMATION OF THE LATENT IMAGE
The film emulsion is made of silver bromide crystals and
silver iodide crystals that is precipitated in gelatin and
layered on a thin sheet of transparent base
The silver halide crystals are chemically sensitized by
the presence of sulphur compounds which cause
physical irregularities in the crystal produced by iodide
ions , and these are called latent image sites
8.
The function of latent image site is to begin the process
of image formation by trapping the electrons generated
when the emulsion is irradiated
When the silver halide crystals
are irradiated , the
electron released changes bromide ion into bromine
atom. This will produce kinetic energy with which it
moves in the crystal and strikes the image site imparting
a negative charge to that region
9.
Free positively charged interstitial silver ions are
attached to the negative latent image site and neutralize
the image site with the result that an atom of metallic
silver is deposited at the site. After exposure e of a film
to radiation, the aggregate of silver atoms at the latent
image sites, comprises the latent image. It is the
metallic silver at each latent image site that catalyses
the development of the halide crystal in which it formed
and renders the crystal sensitive to development and
image formation
10. FILM PROCESSING
The primary action of processing solution is to convert
the crystals with latent image into black metallic silver
grains that can be visualized and to remove the
unexposed silver bromide crystals
Latent image is made visible through the following
processing procedures
The film is placed in a chemical known as the
developing solution for a specific amount of time and at
a specific temperature
11.
Developer distinguishes between unexposed and
exposed silver halide crystals
Reduces exposed silver halide crystals into metallic
silver and creates black areas in the radiograph
Unexposed remains unaffected
Rinsed in water to remove remaining developer
solution
12.
Next , the film is placed in a special chemical known as
fixer solution
Fixer solution removes the unexposed silver halide
crystals and creates white or clear areas on dental
radiograph
Following the fixing process , the film is washed in water
to remove any remaining traces of chemical solution
Drying : after rinsing the film , it is dried. The film is
placed in a drying cabinet or hung up in a well ventilated
dust free room
13. FILM PROCESSING SOLUTIONS
These may be obtained in the following forms :
Powder
Ready to use liquid
Liquid concentrate
The special chemical solutions are :
Developer solution
Fixing solution
14. DEVELOPER SOLUTION
REDUCING AGENTS
Hydroquinone : - It is concerned with the production of high
contrast in the radiograph
Metol or Elon :- It helps develop the shades of gray on the
film and brings out the details
When used together hydroquinone and metol produce an
adequate contrast and detail, at 20 degree C
Metol phenidone :- this serves as the first electron donor
that converts silver ions to metallic silver at the latent image
site
15.
PRESERVATIVE
Sodium sulphite :- this inhibits the tendency of
the developing agent to combine with the oxygen
dissolved in water or in the air. Therefore acts as a
preservative and keeps the solution in an usable
condition for several weeks
Oxidation of the developing agents forms colored
substances which would stain the film and add to
the film fog
16.
ACTIVATOR
Potassium carbonate or sodium carbonate :provide and maintain the degree of alkalinity in
which the developing agent can function. Also
known as accelerator
RESTRAINER
Potassium bromide :- it slows down the reduction
action of the developing agents
17.
HARDENER
Glutaraldehyde :- to prevent the emulsion from
softening and sticking to the rollers
FUNGICIDE :- to prevent bacterial growth
BUFFER :- to maintain p H
SOLVENT :- water
18. FIXING SOLUTION
CLEARING AGENT
Ammonium thiosulphate :- removes silver bromide
PRESERVATIVE
Sodium sulphite :- prevents oxidation of clearing agent
ACIDIFIER
Acetic acid :- keep the fixer pH constant
HARDENER
Aluminum chloride :- form complex with gelatin
SOLVENT
Water
19.
REDUCTION
A photographic reducer contains an oxidizing
agent, potassium ferricyanide which oxidizes the
silver to silver ferrocyanide , which in turn is
dissolved by the solution of sodium thiosulphate.
This is known as the farmer’s reducer and consists
of two solutions
Solution A : potassium ferricyanide 75 grams
Solution B : sodium thiosulphate crystals 240
grams
20.
CHEMICAL INTENSIFICATION OF
RADIOGRAPHS
In – 4 chromium intensifier
In -5 silver intensifier
Copper iodide intensifying solution
XR -10 intensifying solution
Line toner solution
22. GENERAL
LAYOUT
Size of the darkroom :- 3 feet x 3 feet for an
individual dentist and 16 to 20 square feet for a
group
Size will vary depending on :-
Volume of radiographs processed
Number of persons using darkroom
Type of processing equipments
Space required for duplication of film and storage
23.
REQUIREMENTS OF DARK ROOM
Sufficient space
Should be 3 feet away from processing tank
Should be ventilated
Temperature of 70 degree and humidity of 50-70%
is maintained
Should include hot and cold running water
24. ILLUMINATION
Complete darkness and must exclude all visible
light- light tight or light proof is accomplished by :exclusion of all external lights
use of light tight door
Use of both white light and safe light
White light illumination is required during cleaning
tanks and preparing the solutions
25. SAFE
LIGHT ILLUMINATION
Should be of low intensity
3 zones :i.
dimmest zone
ii.
medium zone
iii.
bright zone
Excessive exposure of film to safe light illumination
will result in fog, 3 factors :-
26.
Type of filters:-
Moralite filter
Wratten series 6 B filters
Red GBX-2 safe light filter
Intensity of illumination :-
Wattage of bulb should be 7 ½ to 15 watts
The distance of the safe light above the work area
should be 4 feet
Time of exposure :- more the film is exposed to
safe light, more chance of film fogging
27. TESTS
FOR CHECKING UNSAFE
ILLUMINATION
Coin test / penny test :- evaluate fogging caused by
inappropriate safe light conditions
Check for light leak
28. PROCESSING
EQUIPMENT
MANUAL / HAND / TANK PROCESSING
Simplest and most efficient procedure for developing with
accurate control
Processing tank consists of :-
Master tank
Insert tank
Tanks are made of :-
Stainless steel ( ISI type 316 SS with 23 % Mo )
Enamel
Earthenware
Hard rubber
29. OTHER
REQUIREMENTS INCLUDE :
Thermometer
Timer
Drying racks
Stirring rod or stirring paddle
Plastic apron
30. METHODS OF PROCESSING
Manual method
Time temperature method
Visual method
Rapid processing method
Automatic method
Monobath method
Day light method
Digitized processing method
Self developing method
31. TIME
TEMPERATURE METHOD
Mass processing of radiographs
Method
Replenish solutions
Stir the solutions
Mount the film on hangers
Processing is carried out at a temperature of 6870degree F and timer is fixed
Dry the film
32. VISUAL
METHOD
Advantage :- film can be developed to the contrast
and detail desired for the particular subject
Disadvantage
:-
film
has
to
be
individually and is very time consuming
processed
34.
AUTOMATIC METHOD
Automatic dunking models : produces a washed film that
still has to be dried
Miniature roller type : produces a dried film
Advantages :-
Process takes less than 4- 7 minutes
Uniformity
Less floor space required
No wet films to be handled
Density and contrast are consistent
35.
Disadvantages
Quality is not as high as manually developed
radiograph
More grain is evident in the final image
High cost of equipment and maintenance
Mechanism
An in line arrangement consisting of a transport
system
Function of roller
Move the film through developing solutions
Motion keeps solutions agitated
36.
MONOBATH METHOD
Developer and fixer are combined in one solution
Advantage : It is ideal for root canal treatment or in cases of
quick spot diagnosis
Disadvantages :Alkaline type of fixer very rapidly oxidizes under
atmospheric conditions
Results are not satisfactory as in conventional
processing as the fixing starts while the developing
process is in progress
37.
DAY LIGHT METHOD
No need of darkroom
Emulsion consists of yellow dye and the film
appears yellow and black
38.
DIGITIZED PROCESSING METHOD
CR system : IP cassette is used instead of cassette
with an X-ray film
DR system : cassette is replaced by a sensor which
is directly connected to the workstation
39.
SELF DEVELOPING FILMS
Advantages :No dark room is required
Time saving
Disadvantages :Poor image quality
Image deteriorates with time
No lead foil inside the packet
Film packet is flexible and easily blent
Films are difficult to use in positioning holders
