Processing of X-Ray Film

After the exposure of x-ray film the silver halide crystals get chemically altered by beam of photons. These chemically altered silver bromide crystals constitute the latent (invisible) image on the film.

The processing is the procedure to converts the latent image into one that can be visualized.

  • Silver halide crystals also contain a few free silver ions (interstitial silver ions) in the spaces between the crystalline lattice atoms.
  • The crystals are chemically sensitized by the addition of trace amounts of sulfur compounds, which bind to the surface of the crystals.
  • The sulfur compounds play a crucial role in image formation.
  • Along with physical irregularities in the crystal produced by iodide ions, sulfur compounds create sensitivity sites (the sites in the crystals that are sensitive to radiation).
  • When the silver halide crystals are irradiated, x-ray photons interact primarily with the bromide ions by Compton and photoelectric interactions.
  • These interactions result in the removal of an electron from the bromide ions. By the loss of an electron, a bromide ion is converted into a neutral bromine atom.
  • The free electrons move through the crystal until they reach a sensitivity site, where they become trapped and impart a negative charge to the site.
  • The negatively charged sensitivity site then attracts positively charged free interstitial silver ions.
  • When a silver ion reaches the negatively charged sensitivity site, it is reduced and forms a neutral atom of metallic silver. The sites containing these neutral silver atoms are now called latent image sites.
  • This process occurs numerous times within a crystal.
  • The overall distribution of latent image sites in a film after exposure constitutes the latent image.
  1. Development – Converts latent image to black metallic silver.
  2. Rinsing (stop bath) – Removes excess developer.
  3. Fixing and Hardening – Dissolves out unexposed silver halide crystals.
  4. Washing – Removes products of processing.
  5. Dry – Removes water.
  • Developer reduces all exposed silver ions (those with a latent image) to metallic silver grains by donating electrons.
  • This reduction process is restricted to crystals containing latent image sites.

It slowly starts to reduce silver bromide halide crystals that do not contain a latent image and results in overdeveloping of the Image (film fog or dark radiograph).

Contains four components (DAPR):

  1. Developer.
  2. Activator.
  3. Preservative.
  4. Restrainer.
    1. Developer:

Two developing agents:

    1. Pyrazolidone-type compound (Phenidone)
      • Serves as the first electron donor.
      • Converts silver ions to metallic silver at the latent image site.
      • This electron transfer generates the oxidized form of Phenidone.
    2. Hydroquinone (paradihydroxy benzene)
      • Provides electron to reduce the oxidized phenidone back to its original active state.
  1. Activator
    • The developers are active only at alkaline pH values (10).
    • Alkali compounds such as sodium or potassium hydrozide.
    • Buffers used usually sodium bicarbonate.
    • It also swells the gelatin thus providing more diffusion of developing agents into the emulsion.
  2. Preservative
    • Contains Sodium sulphite (an antioxidant or preservative).
    • Protects developer from oxidation by atmospheric oxygen and thus extends their useful life.
    • Also combines with the brown oxidized developer to produce a colorless soluble compound.
  3. Restrainer
    • Bromide, usually as potassium bromide and benzotriazole.
    • Restrain development of unexposed silver halide crystals.
    • Act as antifog agent and increase contrast.

Developer also becomes inactivated by:

  • Release of bromide ions and other by-products into solution.
  • Exposure to oxygen.

These actions produced seasoned solution.

  • Developer should be replenished with fresh solution each morning.
  • The recommended amount to be added daily is 8 ounces of fresh developer (replenisher) per gallon of developing solution.
  1. Visual method
    • In this method exposed x-ray film is immersed into developing solution for about 10 seconds then remove and observed in the safelight.
    • If adequate image is obtained then it is put for rinsing, otherwise reinserted in the developing solution.
    • This method is highly objective in nature and doesn’t give consistent quality.
  2. Time temperature method
  3. For intraoral film processing in conventional solutions, use the following development times:
    Temprature Development Time
    680 F 5 minutes
    700 F 41/2 minutes
    720 F 4 minutes
    760 F 3 minutes
    800 F 21/2 minutes
  4. Modified time temperature method:
    This method depends upon the temperature of solution; the developing time is divided on daily basis. A chart can be prepared by specifying developing time for a range of daytime temperature.
    Advantage
    Temperature need not be maintained at particular level and at the same time consistent image quality can be gained.
    Disadvantage
    For every brand of developer separate time temperature chart should be prepared.
  • When the film is removed from the developer the gelatin emulsion is soft and swollen and contains chemicals which are removed by rinsing.
  • Films are rinsed in water for 30 seconds with continuous, gentle agitation.
  • Rinsing dilutes developer, slowing the development process.
  • It also removes the alkali activator, preventing neutralization of the acid fixer.

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.

  • Fixer dissolves and removes the undeveloped silver halide crystals.
  • If these crystals are not removed, the resultant image is dark and non diagnostic.
  • It also hardens and shrinks the film emulsion.

Fixer contains:

  1. Clearing agent.
  2. Acidifier.
  3. Preservative
  4. Hardener.
  1. Clearing agent
    • An aqueous solution of ammonium thiosulfate (“hypo“) dissolves the silver halide grains.
    • It forms stable, water soluble complexes with silver ions, which then diffuse from the emulsion.
  2. Acidifier
    • Contains an acetic acid buffer system (pH 4 to 4.5).
    • It promotes good diffusion of thiosulfate into the emulsion and of silver thiosulfate complex out of the emulsion.
  3. Preservative
    • Ammonium sulfite is the preservative in the fixing solution.
    • It prevents oxidation of the thiosulfate clearing agent, which is unstable in the acid environment of the fixing solution.
  4. Hardener
    • Aluminum sulfate.
    • Aluminum complexes with the gelatin during fixing and prevents damage during subsequent handling.
    • Reduce swelling of the emulsion during the final wash.

There is gradual loss of film density because the grains of silver slowly dissolve in the acetic acid of the fixing solution.

  • Place film in the fixer for 10 minutes.
  • Agitate for 5 of every 30 seconds to eliminate bubbles and brings fresh fixer into emulsion. 
  • Wash and dry.
  • Place the hanger in running water for at least 10 minutes.
  • After the films have been washed, remove surface moisture by gently shaking excess water from the films and hanger.
  • Dry the films in circulating, moderately warm air.
  • Fixer solution is replenished daily at the rate of 8 ounces per gallon.

The developer can be identified by its soapy feel (alkali) and the fixer by its vinegary odor when fresh and acid taste.

Darkroom is a room in the dental office set aside for radiographic processing.

  • Keep it clean.
  • Change solutions regularly.
  • Keep accurate records of processed radiographs.
  • Maintain a quality-assurance program.
  • Light tight and have safelight and white light illumination.
  • Processing tanks.
  • Thermostatically controlled supply of water.
  • Thermometer.
  • Timer.
  • Film hangers.
  • Drying racks.
  • Storage space.
  • Volume of radiographs to be processed.
  • Number of dental professionals handling processing.
  • Type of processing to be done.
  • Space required for duplicating, drying, and storage. 
  • The darkroom should be at least 4 x 5 feet (1.2 x 1.5m).
  • It should be lightproof (light-tight door or door less maze is used).
  • The door should have a lock (prevent accidental opening).
  • Room must be well ventilated (it exhaust the heat from the dryer and moisture from the drying films).

Dark room should be:

  • Convenient in relation to the Radiographic room.
  • 1.6 mm (1/16 inches) lead required to shield walls adjacent to the radiographic rooms.
  • Windows should be avoided.
  • Away from damp or hot areas.
  • Accessible to plumbing and electrical se
  • Walls should be of light in color (Easy to wipe out and clean).
  • Floor should be chemical resistant and stain proof asphalt tiles, porcelain tiles, clay tiles. Add non skid abrasive to avoid slipping.

Entrance:

  1. Single door entrance
  • Simplest and cheapest type.
  • Weather stripping around the door frame.
  • This type can cause accidental exposure of film to white light.
  1. Double door entrance
  • Have two doors.
  • One leading in and other out with a short hallway in between.
  • One door cannot be opened unless the other is closed.
  • This type can cause trapping.
  1. Maze or Labyrinth type entrance
  • Has no door so people can enter and exit at any given moment.
  • Takes up too much building space.
  1. Revolving door entrance
  • Most efficient but most expensive type.
  • Composed of two black cylinders.
  • The outer is fixed.
  • Inner is the revolving door with only one opening. 
  • Adequate removal of stale humid air.
  • Supply of fresh air.
  • Provide satisfactory working conditions for staff.
  • Good film handling and storage conditions.
  • Efficient automatic processor performance.
  • If unused film is stored in the x-ray room, then it must be stored in a container made up of a lead container or something equivalent to 1.6 mm of lead.
  • Photographic materials should be stored at temperatures less than 240 C, preferably in the range of 15 to 210C. Open packages of film should be stored in an area with humidity ranging between 40 and 60 %.

Any illumination that does not affects the x-ray film.

X- ray films are very sensitive to blue-green region of the spectrum (relatively short wave length).

X- ray films are less sensitive to yellow and red region of the spectrum (relatively long  wave length).

Safe-light should be composed of red light.

  • Safelight should be placed above the work area on the wall behind the processing tanks and somewhat to the right of the fixing tank.
  • The safelight should have a clear 7.5 or frosted I5-watt bulb and safelight filter (red GBX-2).
  • It should be mounted at least 4 feet above the surface where opened films are handled.
  • Open a exposed film packet and place the bare test film in the area where the films are usually unwrapped.
  • Place a penny on the film and leave it in this position for 5 minutes.
  • Develop the test film as usual.
  • If image of penny appears on resultant image then room is not light safe for particular film tested.

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

  • It consists of master tank about 20 x 25 cm (8 x 10 inches) that can serve as a water jacket for two removable inserts that fit inside.
  • Insert tanks usually hold 3.8 L (1 gallon) of solution (developer/ fixer) and are placed within the outer, larger master tank.
  • Master tank must have hot and cold running water and a means of maintaining the temperature between 600 and 750 F.
  • Use to determine the temperature of developer solution.
  • Optimum temperature is 680 F, below 600 F chemical works to slowly (underdevelopment).
  • Above 750 F chemical works too fast (film fog).
  • Thermometers may contain alcohol or metal not mercury.

Two types:

  • Tank thermometer: Marked with centigrade and Fahrenheit, has steel clip on back formed in to hook.
  • Floating, stirring rod type of thermometer.

Timer signals the radiographer that the film must be removed from current processing solution.

  • Drying racks can be mounted on a convenient wall for film hangers.
  • Drip trays are placed underneath the racks to catch water from wet films.
  • Cabinet dryers accelerate drying.
  • Excessive heat must be avoided to prevent emulsion damage.
  • These solutions typically develop films in 15 seconds and fix them in 15 seconds at room temperature.
  • Developer contains contain a higher concentration of hydroquinone and alkaline pH which causes the emulsion to swell more, thus providing greater access to solution.
  • Resultant images often do not achieve the same degree of contrast as films processed conventionally.
  • They may discolor over time if not fully washed. 

In automatic processing there is:

  • No stop bath between developer and fixer as rollers remove the chemicals.
  • Higher temperatures for automatic processors, therefore different chemicals required.
  • Hardener placed in developer in automatic processors.
  • Additional hardener is added to the fixer solution.
  • Because of the daylight-loader a darkroom is not required.
  • Because of the heater in the automatic processor, the process is a “dry to dry” process.
  • Self-developing films are an alternative.
  • The x-ray film is presented in a special sachet, containing developer and fixer.
  • Following exposure the developer tab is pulled, unveiling developer solution, which is milked down towards the film and massaged around it gently.
  • After about 15 seconds, the fixer tab is pulled to release fixer solution, which is similarly milked down to the film.
  • After fixing the used chemicals are discarded and the film is rinsed thoroughly under running water about 10 minutes.

It uses a roller transport system.

  1. Processor Housing: Encases all the component parts of the automatic processor.
  2. Film Feed Slot: Opening on outside of the processor housing used to insert unwrapped films into automatic processor.
  3. Roller Film Transporter: System of rollers (propelled by motor driven gears and belts) used to move the film rapidly through the developer, fixer, water, and drying compartments.
  • Rollers produce wringing action that removes the excess solution from the emulsion.
  • Prepare darkroom, if daylight loader is not part of automatic processor.
  • Close and lock the door of darkroom.
  • Turn off the overhead white light and turn on the safelight.
  • For intraoral films, carefully unwrap each exposed film over a clean working surface.
  • For extra-oral films carefully remove the film from the cassette. -Handle all the films by the edges only.
  • Insert each unwrapped film into the film feed slot of the processor, one at a time.
  • Allow at-least 10 sec between the insertion of each film.
  • Do not turn the films sideways or insert too quickly, they will overlap; overlapped films results in non diagnostic radiographs.
  • After films are inserted, allow 4-6 min for automated processing to occur. Retrieve the processed radiographs from the film recovery slot on the outside of the automatic processor. 
  • Time saving.
  • Constant film quality is achieved, due to fixed processing cycles.
  • Need for dark room is eliminated.
  • Less floor space is required.
  • Chemicals can be replenished automatically by machine.
  • Large number of films can be processed continuously. 
  • Equipment is relatively expensive.
  • Strict maintenance and regular check up is required.
  • Dirty rollers produce marked films.
  • Films may get lost in the tank.
  • The primary ingredient of concern in processing solutions is the dissolved silver found in used fixer.
  • Another material of concern is the lead foil found in film packet.
  • The lead foil “is separated from the packets and collected until enough has been accumulated to sell to a scrap metal dealer.
  • Silver may be recovered from the fixer by using either metallic’ replacement or electroplating methods.
  • Metallic replacement uses cartridges through which waste solutions are poured. In this process, iron goes into the solution and the silver precipitates as a sludge.
  • Dental offices also should consider using companies licensed to pick up waste materials.
  1. Processing error
  • Underdevelopment
  • Depleted developer solution
  • Diluted or contaminated developer
  • Excessive fixation
  1. Underexposure
  • Insufficient milliamperage.
  • Insufficient peak kilovoltage.
  • Insufficient time
  • Film-source distance too great.
  • Film packet reversed in mouth.

Processing errors

  • Overdevelopment
  • Developer concentration too high.
  • Inadequate fixation.
  • Accidental exposure to light.
  • Improper safe lighting.

Over exposure

  • Excessive milliamperage.
  • Excessive kilovoltages.
  • Film source distance too short.
  • Underdevelopment
  • Underexposure
  • Excessive peak kilovoltage.
  • Excessive film fog.

Film fog evidenced by dull-gray low contrast image.

What are the types of film fog?

  • Light fog
  • Radiation fog.
  • Processing (chemical) fog
    1. Light fog
      • Light leaks in darkroom.
      • Improper safelight; check wattage, distance, and filter film compatibility.
      • Turning overhead (white) light on too soon (be certain films have cleared in fixer first).
    2. Radiation fog
      • Improper storage; insufficient protection of film next to x-ray machine.
    3. Processing (chemical) fog
      • Developer temperature too high.
      • Over strength developer.
      • Contaminated developer
      • Prolong development for temperature.
  • The term phalangioma was used by Dr. David F Mitchell it refers to the image of phalanx or fingers appearing the film.
  • It occurs when patient holds the film in the mouth in an incorrect way which results in exposing the image of fingers on the radiograph.
  • Fingerprint contamination.
  • Black wrapping paper sticking to film surface.
  • Film in contact with tank or another film during fixation.
  • Film contaminated with developer before processing.
  • Excessive bending of film.
  • Static discharge to film before processing.
  • Excessive roller pressure during automatic processing.
  • Dirty rollers in automatic processing.
  • Film contaminated with fixer before processing.
  • Film in contact with tank or another film during development.
  • Excessive bending of film.
  • Depleted developer.
  • Depleted fixer
  • Insufficient washing
  • Contaminated solution.
  • Movement of patient.
  • Movement of x-ray tube head.
  • Double exposure.
  • Top of film not immersed in developer.
  • Misalignment of x ray tube head.
  • Abrasion of image during processing.
  • Excessive time in wash water.
  • Slow “sulfurizing” of image due to retained hypo (thiosulfate) from the fixer reacting with metallic silver image to form silver sulfide.

Radiographers report many unexplained work related symptoms attributed to “darkroom disease symptoms” such as headache, skin rash, mouth sores, blurred vision, palpitation, and chemical taste.

  • Inhalation: Occupational/glutaraldehyde induced-asthma, chemical/ metallic taste, sore throat, sinusitis, catarrh, nose bleeds, rhinitis.
  • Direct contact: Dermatitis, skin rash.
  • Indirect contact (vapors): Eye irritation.
  • Ingestion: Sore throat, abdominal pain, cramps, vomiting, diarrhea, coma, liver and kidney damage
  1. Daily
    • Compare radiographs with reference film.
    • Enter findings in retake log.
    • Replenish processing solutions.
    • Check temperature of processing solutions.
    • Make step-wedge test of processing system
  2. Weekly
    • Replace processing solutions.
    • Clean processing equipment.
    • Clean view boxes.
    • Review retake log.
  3. Monthly
    • Check darkroom safe-lighting.
    • Clean intensifying screens.
    • Rotate film stock.
    • Check exposure charts.
  4. Yearly
    • Calibrate x-ray machine.
  1. Processing the radiograph. Available from: http://www.columbia.edu/itc/ hs/dental/sophs/material/processing.pdf
  2. Manual of Darkroom Technique – World Health Organization. Available from: apps.who.int/medicinedocs/documents/s17683en/s17683en.pdf
  3. X-ray facility tips. Available from: http://www.healthvermont.gov/sites /default/files/documents/2016/11/Env_RAD_xray_facility_tips_darkroom_fog.pdf
  4. White S.C, Pharoah M.C. Processing X-ray film. Oral Radiology- principles and interpretation; 2011:6th ed.
  5. Haring Joen M. Lannucci, Howerton Laura Jansen. Dental Radiography-Principles and Techniques; 2006: 3rd
  6. Langland Olaf E.,Langlais Robert P.,Preece John W. Principles Of Dental Imaging 2nd edition;2002:59
  7. Radiographic films fault and artifacts in dentistry. Available from: https://www.juniordentist.com/radiographic-film-faults-and-artifacts-in-dentistry.html
  8. Sarafisa P, Dallasb D, Sotiriadouc K, Stavrakakisd P, Chalarise M. ‘Dark room’ disease. Journal of Environmental Protection and Ecology 2010;11:506-14.
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