RADIOGRAPHIC PROCESSING AND DARK ROOM

Presented by:Pragy MallikRoll no:21Bds 2nd batch

Formation of the latent image When a beam of photons exits an object and exposes an x-ray

film, it chemically changes the photosensitive silver halide crystals in the film emulsion.

These chemically altered silver bromide crystals constitute latent image on the film.

Silver bromide crystal in the emulsion of an x-ray film contains mostly silver and bromide ions in a crystal lattice. There are also free interstitial silver ions and areas of trace chemicals that form sensitivity sites.

Exposure of the crystal to photons in an x-ray beam results in release of electrons, usually by interaction of the photon with a bromide ion. When electrons reach a sensitivity site, they impart a negative charge to this region

Free interstitial silver ions (positive charge) are attracted to the negatively charged sensitivity site.

Silver ions after reaching sensitivity site, acquire an electron and become neutral silver atoms. These silver atoms now constitute a latent image site. The collection of latent image sites over the entire film constitute the latent image.

Film processing Film processing refers to a series of steps that produce a visible

permanent image on a dental radiographs.

Aims

• To convert latent image (invisible) on the film to a visible image.

• To preserve the image so that it is permanent and doesn’t disappear from a radiograph.

Processing solutionsProcedure:i. Immerse exposed film in developer

ii. Rinse developer off film in water bath

iii. Immerse film in fixer

iv. Wash film in water bath to remove fixer

v. Dry film and mount for viewing

Emulsion changes during film processing

Developing solutions Developer reduces all silver ions in the exposed crystals of silver

halide to metallic grains.

To produce a diagnostic image, this reduction must be limited to crystals containing latent image sites.

For this, reducing agents used as developer are catalyzed by neutral silver atoms at the latent image sites.

When an exposed film is developed, initially there is no visible effect, later density increases, rapidly at first and then more slowly.

Development of unexposed crystals results in chemical fog on the film.

Components I. Developer

II. Activator

III. Preservative

IV. Restrainer

Developer Converts the exposed halide crystals into metallic silver.

Developing agents: phenidone and hydroquinone.

Phenidone: first electron donor that converts silver ions to metallic silver at

the latent image site. This electron transfer generates oxidized form of

phenidone.

Hydroquinone: provides electron to reduce the oxidized phenidone back to

its original active state so that it can continue to reduce silver halide grains

to metallic silver.

Activator Developers are active only at ph value around 10.

This ph is achieved by addition of alkali compounds such as sodium or potassium hydroxide.

Theses activators also cause gelatin to swell so that developing agents diffuse more rapidly into the emulsion to reach silver bromide crystals.

Preservative Sodium sulfite is used as a preservative which extends the useful

life of the solution.

Preservative combines with developer to produce a compound that stains image brown if not washed out.

Restrainer Bromide containing compounds are added to restrain

development of unexposed silver halide crystals.

Restrainers act as antifog agent and increase contrast.

Developer Replenisher Developing solutions should be replenished with fresh solutions

each morning to prolong the life of the used developer.

Recommended amount to be added daily: 8 ounces of fresh developer per gallon of developing solution. This assumes development of 30 periapical or 5 panoramic films per day.

Rinsing After development, film emulsion swells and becomes saturated

with developer.

Film are rinsed in water for 30 sec with continuous, gentle agitation before they are placed in fixer.

Use: dilution of developer

slowing development process

removes alkali activator preventing neutralization of acid fixer

Fixing solutionUse: o Removes undeveloped silver halide crystals from the emulsion.

o If not removed, results in dark and non diagnostic radiograph.

o Hardens and shrinks the film emulsion.

Should be replenished daily at the rate of 8 ounces per gallon.

Components I. Clearing agent

II. Acidifier

III. Preservative

IV. Hardener

Clearing agent Aqueous solution of ammonium thiosulphate dissolves the

unexposed silver halide grains.

Forms stable, water soluble complexes with silver ions, which diffuse from the emulsion.

Excessive fixation: gradual loss of film density because the grains of silver slowly dissolve in the acetic acid of the fixing solution.

Acidifier Acetic acid buffer system (ph 4- 4.5) is used to keep the fixer ph

constant.

Acidic ph is used to promote good diffusion of thiosulphate into emulsion and of silver thiosulphate complex out of the emulsion.

Also inactivates any residual developing agents in the film emulsion, blocking continued development of any unexposed crystals while the film is in the fixing tank.

Preservative Ammonium sulfite is the preservative

It prevents oxidation of thiosulphate clearing agent, which is unstable in the acid environment of fixing solution.

Hardener Aluminium sulfate is used.

It complexes with gelatin during fixing and prevents damage to the gelatin during subsequent handling.

It also reduce swelling of the emulsion during final wash.

This lessens mechanical damage to the emulsion and shortens drying time.

Washing After fixing, processed film is washed in water to remove all

thiosulfate ions and silver thiosulfate complexes.

washing efficiency decreases rapidly when the water temperature decreases to less than 60ºF.

Improper washing discolors and causes stains, which are most apparent in radiopaque areas.

DARKROOM AND EQUIPMENTDarkroom Requirements:

• Lightproof: to prevent film fogging and loss of contrast.

• Light tight door or doorless maze: should have lock to prevent accidental opening and ruining of opened films

• Well ventilated: for the comfort of people working in the area and to exhaust moisture from drying films.

• Room temperature: for developing, fixing and washing solutions.

Safelighting Should have both white illumination and safe lighting.

Safe lighting is low intensity illumination of relatively long wavelength(red) that does not rapidly affect open film but permits one to see well enough to work in the area.

Should have 15 watt bulb or a clear 7.5 watt bulb and should be mounted at least 4 feet above the surface where films are handled.

Film handling under a safe light should be limited to about 5minutes because film emulsion shows some sensitivity to light from a safelight with prolonged exposure.

Penny test A radiographic film is sensitive to visible light and x-rays.

Excessive exposure to safe light or an improper safe light condition can lead to exposure of the film resulting in film fog.

Such film appears dark and have a muddy gray appearance.

The safe lighting conditions in the dark room can be evaluated using a coin test, called penny test.

Procedure: I. Open the packet of an exposed film and place the film in the

area where the films are usually unwrapped and clipped on the film hanger.

II. Place a coin on the film and leave it in this position for about 5minutes.

III. Develop the film as usual. If the image of the coin is visible on the resultant film, the room is not light safe.

Photograph demonstrating penny test

Manual Processing Tanks The tank must have hot and cold running water and a means of

maintaining the temperature between 60ºF and 75ºF.

Size: 20cm*25cm (8inches*10inches) that can serve as a water jacket for two removable inserts that fit inside.

Insert tanks hold 3.8 L of developer or fixer and are placed within the outer, larger master tank.

Outer tank holds the water for maintaining the temperature of developer and fixer in the insert tanks and for washing films.

Developer is placed on the left side and fixer is on the right.

All three tanks should be made of stainless steel, which does not

react with the processing solutions and is easy to clean.

Should have a cover to reduce oxidation of processing solutions,

protect developing film from accidental exposure to light, and

minimize evaporation of the processing solutions.

Thermometer Temperature of the solutions should be closely controlled.

A thermometer can be left in water circulating through the master tank to monitor the temperatureand ensure that the water temperature regulator is working properly.

Thermometers are clipped onto the side of the tank.

Thermometers may contain alcohol or other metal, but should not contain mercury because they could break and contaminate the processor or solutions.

Timer X-ray film must be exposed to the processing chemicals for

specific intervals.

An interval timer is indispensable for controlling development and fixation times

Drying Racks

Two or three drying racks can be mounted on a convenient wall for film hangers.

Drip trays are placed underneath the racks to catch water that may run off the wet films.

An electric fan can be used to circulate the air and speed the drying of films, but it should not be pointed at the films.

Manual processing procedures1. Replenish solutions2. Stir solutions3. Mount film on the hangers4. Set timer5. Develop6. Rinse7. Fix8. Wash9. Dry

Temperature (ºF) Development time (minutes)

68 5

70 4½

72 4

76 3

80 2½

Rapid processing chemicals Rapid processing solutions typically develop films in 15seconds

and fix them in 15 seconds at room temperature.

They have same general formulation but concentration of hydroquinone is higher and ph is more alkaline.

These are advantageous in endodontics and in emergency situations, when short processing time is essential.

Visual method It is always recommended to use the time temperature controlled

method of processing films. However, when the facility of temperature controlled processing is not available, the visual method can be used.

Here, no predetermined time for the placement of the film in the developer solution is used. The exposed film is placed in the developer solution and taken out at regular intervals and examined under the safe light for the most calcified/radiopaque structures (enamel cap, restorations, artificial crowns) to be evident.

At this point, films are taken out of the developer solution, rinsed in water and placed in the fixer solution.

Disadvantage: inter examiner errors,

films of poor density and contrast

films can be very light or dark making it unfit for

diagnostic evaluation.

Salvaging dark radiographs• Most common method of reducing,or lightening, dark films is described by E.

Howard farmer in 1884.

Potassium ferrocyanide + silver silver ferrocyanide +potassium ferrocyanide

• Silver ferrocyanide is then made soluble by its reaction with thiosulphate, and thus can be removed from the film.

• However, this reducer is considered dangerous because it contains ferrocyaniode.

• Other reducers: potassium permanganate and potassium dichromate.

• Wakefield in 1970, described a single solution reducer with a very long life.

The reducing solution(Modification of Wakefield solution) Chemicals used are mixed in order they are listed, in a glass or

ceramic container

a. Copper sulphate crystals(5 ml)

b. Sodium chloride (5 ml)

c. Concentrated hydrochloric acid (5 ml)

d. Water (200 ml)

Lightening a film To lighten a overexposed or overdeveloped film,

it should first be soaked in water to soften emulsion. Rinse in the reducing solution• The film will turn a whitish color as silver chloride is produced on

the surface of the film.• Reduction process should take between 4-10 seconds.• Film is rapidly rinsed in cold water fixed washed

dried

Alternate technique of lightening dark radiographs The dark radiograoh if dry Place in the fixer tank for few minutes.

place on an even surface

use sharp Bard Parker blade to scrape away emulsion one side of the film in a even regular strokes.

Rinse under running tap water

Dried

Automatic processing

Automatic film processing refers to the processing of radiographs using machines specifically designed for that purpose.

Advantages:

• Need for dark room is eliminated.

• Human errors is eliminated

• Is a time saving procedure

Disadvantage

• Costly

• Need for regular maintenance and cleaning of the rollers.

Working mechanism Automatic processor are made up of roller mechanism, which is

driven by by chains, belts or gears which carry the film through the developer, fixing and water tanks.

Roller:

• Used to carry the film at a constant preset rate through the processing solutions.

• Help in drying the film as they squeeze the processing solutions out of the film.

References Clinical manual for oral medicine and radiology:

Ravikiran ongole Oral radiology: White and Pharoah