Radiology Course page 6 – Film Processing-DoctorSpiller.com

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Note: This page relates nearly exclusively to the processing and technology of radiographic film.  As the popularity of digital sensors grows, more and more dentists are abandoning film for computerized images.  Many offices, however, are still wedded to film and its processing.  Thus, it is still essential that anyone involved in radiographic technique understand this material.

After the films have been exposed, they need to be processed. Even with the best placement technique, a cooperative patient, and the highest quality x-ray machine, a film can be rendered non diagnostic during processing. 

Film

X-ray film consists of a blue tinted plastic base covered in an emulsion. The emulsion contains gelatin and silver halide crystals. The silver halide crystals are energized by radiation exposure. When the film is exposed to x rays, the energy reacts with the crystals and creates a “latent image” depending on the different densities that the x-rays have passed through. (The image is “latent” because it does not appear until the film is developed.)  Where there is a filling in the tooth, the halide crystals have very little stored energy because the metal blocks out almost all the x-ray beam. Conversely, interproximal spaces let most of the radiation through, so the crystals in that area are full of stored energy and will precipitate on the film base as black metallic silver particles when the film is developed. The ability for different tissue densities to absorb radiation is called attenuation. Over time the latent image will disappear, so it is best to process the film as soon as possible after exposure. The film should be stored in a refrigerator to slow attenuation if immediate processing is not possible.

When the x-ray is immersed in the developer chemicals, it soaks into the gelatin and reacts with the silver halide crystals. The energized crystals then form metallic silver and bromide. In metallic form, tiny silver particles appear black.  The silver is deposited onto the film and causes the darker areas. The crystals that were not energized are simply washed away by the fixer and that area of the film remains white. So the developer reacts with the energized crystals to make the black areas, and the fixer removes the unenergized crystals and leaves those areas white. If the film comes out too dark, it is because it is overexposed (too much radiation) or overdeveloped. If the film is too light, it is underexposed, underdeveloped, or over fixed.

Manual Processing

Most offices have an automatic processor and tanks for quick processing. At some time in your career you may be called upon to manually develop x-rays. The chemicals and theory are the same in an automatic processor.

The most important factors to consider for developing are the temperature of the chemical and the amount of time the film is allowed to be in contact with the chemical. The higher the temperature of the solution, the less time needed. The preferred condition for manual processing is 4 1/2 to 5 minutes at 68ºF. Keep a non mercury thermometer and a timer accurate in minutes and seconds in the darkroom to check your solution.

After the film is submerged in the developer for the proper amount of time, it must be rinsed in clean, circulating water for 30 seconds. Then the film is submerged in the fixer for at least 10 minutes. The film is rinsed in a compartment with clean, running water for at least 20 minutes to remove all the chemicals and silver. Then the film can be hung to dry or a commercial drying machine or product can be used.

It is imperative that the chemicals in the darkroom are kept in the same order, developer in the first tank, water bath in the center, and fixer in the third tank. The fixer will have a strong vinegary smell. Stir the solutions before submerging the x-rays to mix and distribute the temperature evenly. Use different instruments to stir the developer and the fixer so the two aren’t mixed. Make sure the liquid levels are adequate to cover the films as they are dipped, and add the appropriate chemical if necessary. The best temperature for the chemicals in manual processing is between 65ºF and 75ºF (18ºC to 24ºC). Adjusting the temperature of the incoming water can regulate this temperature. Given time, the chemicals will be the same temperature as the water. The patient’s name and date of exposure should be secured somewhere on the rack. Make sure to turn off the overhead white light and use the safe light. Clip the films firmly to the hanger. Use a timer, don’t rely on your memory. Rinse in between the solutions. The final wash should be 20 to 30 minutes. If the films are in the water for more than an hour, the emulsion may begin to wash off. If the films are left in water overnight, they will be clear in the morning.

Chemicals should always be handled according to the manufacturer’s directions. The chemicals must be checked every day and replenished as needed. Every day, six ounces of the developer should be removed and replaced with six ounces of fresh developer. Stir the solution to mix it well. The fixer should be replenished daily by removing three ounces and replacing it with three ounces of fresh solution. The chemicals must be completely changed according to the manufacturer’s directions. There are many factors that will determine when it is necessary, to change over solutions, such as how many x-rays are developed, exposure of the chemicals to air, and the amount of water dilution. The daily checker film will be a good indicator of when to change the solutions.

Darkroom

The darkroom should be kept clean. The chemical fumes could affect the emulsion of the film so store unused film in another room. There should be plenty of room to work, especially next to the processing tanks. The best internal temperature is 70ºF to 80ºF at 70% humidity. It should be a totally dark room with no cracks in the door where light might sneak in. To check for light leaks, enter the room and close the door with the lights turned off. After your eyes have adjusted (2 or 3 minutes) look around for light. If you see any light leaks, they must be sealed because it could effect the films during processing.

There should be hot and cold running water near the tanks with mixing valves so the temperature can be regulated. A white light source and a good quality safe light should be available at least 4 feet away from the working surface.

Automatic Film Processing

Automatic film processors develop radiographs more quickly than manual processing with consistently good results if the chemicals are maintained. A series of rollers are inside the unit to guide the film through the chemicals. The processor uses a heating element to keep the solutions at a constant temperature, usually 85ºF to 105ºF. This higher temperature shortens the time needed for processing. The action of the rollers helps to disperse the chemicals evenly over the film. A special roller at the end of each tank squeezes off most of the chemical so there is no mixing or diluting of the chemicals.

The two most frequent causes of failure in automatic processors are dirty rollers and expired chemicals. The chemicals should be replenished at the beginning of the day. After four full mouth surveys or panoramic films, the chemicals will need 4 to 6 ounces of new solution. The rollers should be washed once a week with warm running water and soaked for 10 to 15 minutes. Two large extra oral films should be run through the machine to clean the rollers.

Depending on the rate of use, the solutions should be changed every 2 to 6 weeks. Follow the guidelines and use the solutions recommended by the manufacturer. Empty all the chemicals in an orderly manner so they don’t mix.

Follow the manufacturer’s recommendations carefully regarding lubrication, maintenance schedules, and general use. The cover should be kept slightly ajar when the machine is not in use to let fumes disperse and keep moisture from accumulating on the motor. Feed films in at the recommended rate.  Feeding too fast can cause them to stick together.

Film Duplication

X-ray films may need to be duplicated when the patient moves, is referred to a specialist, for preauthorization of insurance, or any other time a record of the x-rays needs to be sent outside the office. The originals stay in the patient’s chart as a permanent record for the office. The operator can use double films (the type with two films in the same packet) for x-rays that will be sent out. They yield two good quality films while exposing the patient to the same amount of radiation.

Film duplicators can also be used, especially when originals have already been taken. The duplicating film is sensitive to light and becomes lighter when exposed. Regular x-ray film becomes darker when exposed to light.

The duplicating procedure takes place in the darkroom with safelights on. The radiographs to be copied are mounted in a special mount designed for duplication with the embossed (raised) dot side down for optimal contact with the duplicating film. Then these radiographs are placed on the duplicator and the duplicating film is placed on top with the emulsion side against the radiograph originals. Expose according to the manufacturer’s recommendations. The film is processed in the same way as regular x-rays.

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