Nematodes

Processing of Xray film

PROCESSING THE RADIOGRAPH

THE STAGES IN THE PRODUCTION OF THE RADIOGRAPH

Many dentists who utilize manual processing, intentionally overexpose patients and under process the radiograph in an attempt to save time resulting in radiographs that are inferior in diagnostic quality because of incomplete development. When an X-ray film has been exposed, it must be processed in order to produce a permanent visible radiographic image that can be kept without deterioration for a number of years. Processing transforms the latent image into a visible image. The term for the several procedures that collectively produce the visible, permanent image is processing and consists of procedures:

1. Exposure - Latent image created.

2. Development - Converts latent image to black metallic silver.

3. Wash [stop bath] - Removes excess developer.

4. Fixing and Hardening - Dissolves out unexposed silver halide crystals.

5. Washing - Removes products of processing.

6. Dry - Removes water.

For manual processing a floating thermometer, a timer, and the time-temperature chart is essential.

1. LATENT IMAGE FORMATION.

The latent (invisible) image formation is the ionization of the exposed silver bromide crystals (by photon energy that emerges from the patient) occurring in the emulsion layer before processing occurs. The primary interaction with the bromide crystals is by Compton and photoelectric interactions, thereby knocking out electrons. Thus, a physical change occurs when the radiograph is exposed. When X-ray photons [or light photons] strike the silver bromide crystals in the emulsion, minute amounts of silver ions are formed on the surface of the crystal, and bromine is liberated and is absorbed by the gelatin. Crystals are purposely constructed with electron traps (sensitivity specks) consisting of sulfur impurities but also because of the addition of silver iodide. Electrons are trapped by the sulfur in the sensitivity specks giving it a negative charge. When this situation is created a latent image is produced in the film emulsion.

AgBr + X-ray photons = Ag+ + Br-Silver bromide Silver ions + Bromine ions

The latent image is formed by deposits of free (ionized) silver ions that cannot be seen or detected by any physical test devised as yet. It remains in the emulsion of the X-ray film until it is changed into a visible silver image by chemical processing procedures. The free electrons move through the crystal until they are attracted to a sensitivity site where they become trapped and impart a negative charge to the site.

2. PROCESSING THE EXPOSED FILM

Exposed radiographs that contain a latent image should be processed as soon as possible as they are more sensitive to energy. Film packets are only to be opened in the darkroom or under safe-light conditions. [in a daylight loader] The developer solution is the first solution into which the films are placed. The developer chemically reduces the energized ionized silver bromide crystals by donating electrons, removing the halides, and precipitating metallic silver in the emulsion layer. The negative charge attracts positively charged free silver ions and is reduced to black metallic atoms. This precipitation corresponds to the black (radiolucent) areas on the radiograph. The concentration of the developer slowly weakens due to the number of films processed, [a chemical reaction], and with time by oxidation of the developer by exposure to air. Traditionally, the developer tank is placed on the left side of the other chemicals solutions

3. RINSING PROCESS/STOP BATH (WASHING)

When the film is removed from the developer the gelatin emulsion is soft and swollen and contains chemicals that are removed by placing the film in a water bath. By rinsing the film in the water the soluble chemicals are removed, the development reaction is stopped, and the alkalinity of the residual developer is reduced. The unexposed silver halide crystals are not water-soluble and will not be washed away. The film should be rinsed for 10-15 seconds in a bath of fresh, running water. The temperature of the water must be as close as possible to the temperature of the developer and fixer to avoid reticulation - uneven expansion and contractions of the emulsion layer. If this step were omitted, the alkaline developer retained by the film would soon neutralize the acid of the fixer. The fixing and hardening action of the fixer would be impaired and as a result, brown stains will be produced on the radiograph within a few weeks. Because the emulsion layer (gelatin) is soft when wet, the film scratches easily. Safe-light conditions must be maintained when transferring the film from the developer to the wash tank and then to the fixing tank to avoid fogging. For automatic processing, there are "squeegy" rollers that remove the chemicals and thus the film goes from the developer solution straight into the fixer.

4. FIXING

The acidic fixing solution removes the unexposed and undeveloped silver bromide crystals from the film emulsion and re-hardens the emulsion that has softened during the development process. For manual processing, if the film is placed in the developer solution for X amount of time it should be placed in the fixer for 2X and in the final rinse for 3X amount of time. "X" is determined by the time-temperature chart. The ideal time to process radiographs in the developer is 680 F for 5 minutes.

However, films may be removed from the fixing solution after five minutes for viewing only in cases of emergency - this procedure is known as wet reading \ viewing. The film must then be placed back in the fixer. If these unwanted silver bromide crystals are not removed, the resultant film will discolor after a few months. If the film is only partially fixed the film will turn brown in color with age. The gelatin protective coating is hardened by the potassium alum so the film will resist abrasion/scratching

5. FINAL WASH

The purpose of the final wash is to remove residual fixer chemicals i.e. acid, thiosulfate, and silver salts from the film. Insufficient washing results in the film turning brown as all the chemicals have not been washed away. If the temperature difference between a developer and / OR fixer and water exceeds 15 F, there is a possibility of unequal swelling and shrinkage of the emulsion layer, commonly referred to as reticulation. Also, prolonged washing tends to make the emulsion soft, and it then scratches more easily.

6. DRYING

In most offices, films are dried merely by hanging them on a rack in the darkroom above a drip tray designed to catch the run-off excess water. Others use a fan to dry the film. The fan should not blow directly on the films. Cabinet dryers are available which are equipped with a fan and heating elements. Wet films are subject to damage from scratching and abrasion if not handled properly. If there is dust in the air, dirt will become easily embedded within the emulsion. Do not remove wet radiographs from their hangers until they are completely dry. In most darkrooms, the developer will be in the left-hand tank as you face the tank, the water bath in the center, and the fixing solution in the right-hand tank. The developer can be identified by its soapy feel, (alkali) the fixer by its vinegary odor when fresh and acid Taste An area of less density, say the pulp, will allow greater penetration of X-rays; therefore more X rays will reach that part of the film. Thus more silver bromide crystals will be energized and more silver will precipitate to give a black or radiolucent outline to the pulp chamber. Areas that have received smaller amounts of radiation will have correspondingly less silver precipitated and will appear gray. Individually if a crystal is energized the whole crystal turns black. The silver bromide behind a gold crown will precipitate no or very little silver as there was minimal energy reaching that area and will appear white, or radiopaque on the radiograph. Gold and amalgam have high z values. The X-ray film is a delicate product, sensitive to many things, e.g. light photons, X-rays and gamma rays, pressure, to various gases and fumes, to heat and moisture and even aging causes a gradual change in it; known as fogging.

PROCESSING CHEMICALS

A. DEVELOPER (Reducing Agent)

Chemical composition of developer solution with their action

a) Hydroquinone [reducer]: brings out sharp contrast in alkaline medium

b) Alkalizer [Na2CO3]: It softens and swells the gelatin emulsion and attracts the exposed silver bromide crystals

c) Preservative [Na. Sulfite] Slows oxidation and therefore preserves the strength of the other chemicals If not present the strength of the other chemicals would rapidly weaken. This explains the darkening of the solution

d) Restrainer [Pot. Bromide]: Restrains the developing agent from the strength. The developing the agent will deposit silver in the unexposed crystals in the emulsion causing a silver deposit (fogging) on the film if the restrainer is not added

e) Vehicle [Water]: Provides a means for the chemicals in the developer to react (Ionize). Water helps to soften gelatin.

The reaction does not occur unless alkalizer is present. The alkali "opens the doors" and permits the developing agents to enter the pores of the emulsion. If the lid is left off the developing tank, the preservative will be rapidly become exhausted by oxidation. In addition to the above, a fungicide is added to prevent the growth of fungi and a buffer is added to maintain the pH within specific limits.

B. FIXING SOLUTION

Chemical composition of fixing solution with their action

a. Fixing Agent [Sodium Thiosulfate (hypo)]: Removes unexposed crystals

b. Preservative [Sodium sulfite]: Prevents deterioration of solution.

c. Hardening agent [Potassium alum]: Shrinks and hardens the gelatin

d. Acidifier [Acetic acid]: Provides acid medium. Alum reacts better in acid medium. Stops developing process

e. Vehicle [Water]:  As above.

The fixing agent removes all the silver halide crystals and therefore if a film is first placed into the fixer solution, the processed film will appear clear.

TYPES OF PROCESSING

1. Manual                    2. Semi-automatic                   3. Fully automatic

SOME DIFFERENCES BETWEEN MANUAL AND AUTOMATIC PROCESSING

1. No stop bath between developer and fixer as rollers remove the chemicals

2. Higher temperatures for automatic processors. Therefore different chemicals required

3. Hardener placed in developer in automatic processors

4. An additional hardener is added to the fixer solution.

5. Because of the daylight-loader, a darkroom is not required.

6. Because of the heater in the automatic processor, the process is a "dry to dry" process.

Rapid processing solutions are used for emergencies and endo where time is of the essence. The film is developed for 15 - 20 seconds and fixed for a similar period of time. The films do not have the same amount of contrast and will discolor with time so they must still be fixed and washed correctly to minimize the discoloration.