Darkroom

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Chapter 12

• Darkroom
• Procedures

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Darkroom Procedures

• To repeat what was previously said about the
  composition of x-ray film, it has a base of
  cellulose acetate covered on both sides with a
  sensitive emulsion of silver halides (silver
  bromide, chloride iodide).
• Today plastic polyester is used.

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Darkroom Procedures

• When this emulsion is exposed to radiation or
  light (from screens or other sources) an
  unexplainable change takes place that cannot be
  seen.
• The change is produced in the physical chemical
  structure of the emulsion.

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Darkroom Procedures

• The change produced on the emulsion depends upon
  the amount of x-ray light reaching it.
• Since the body part being radiographed absorbs
  some of the radiation being directed at it, we
  can see that the amount reaching the screens
  the film depends upon the intervening tissue.

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Darkroom Procedures

• For example, bone absorbs more x-ray fewer rays
  get through to the film/crystals.
• Therefore, fewer crystals are activated.
• The areas outside the parts receive the total
  amount of radiation in this area structural
  change is complete.
• The portion of the film under the lead marker
  (and any other structure that absorbs all the
  radiation) receives none there is no structural
  change to the silver halide crystals.

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Darkroom Procedures

• The other tissue areas absorb the x-rays in
  varying degrees depending upon the thickness
  density of the parts thus the film screens
  under these parts receive varying degrees of
  x-ray the screens glow in varying degrees
  thus the change in the emulsion varies from place
  to place.
• A Latent image is formed in this way.

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Darkroom Procedures

• We can therefore see that the latent image must
  be a complete one.
• The purpose of dark room procedures is to change
  the latent image to a photographic one.

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Film Processing Chemicals

• Various chemicals are used in the processing of
  the radiographic film.
• Of the ones discussed here, the developer the
  fixer must be used the developer replenisher,
  the fixer replenisher the acid stop-bath may or
  may not be used.

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Film Processing Chemicals

• There are other chemicals used for special
  purposes (intensification of under-developed
  film, reduction of over-developed film), but they
  will not be discussed.
• Directions for their use will be found on the
  package.

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The Developer

• Developing is actually the reduction of the
  exposed silver halides to metallic or elemental
  silver (the converting of the latent image to a
  visible image).
• The developer causes a reaction of the silver
  halide crystals thus makes them visible.

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The Developer

• This is done through a pair of redox reactions
  where an electron is made available to unite with
  a silver ion that has a single () charge (from
  light hitting the film), thus reducing the silver
  ion to metallic/elemental silver.

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The Developer

• Reducing Agents
• change the exposed silver halides to black
  metallic silver elon (for detail) is balanced
  with hydroquinone (for contrast).
• Accelerator/Activating
• maintains the proper alkalinity for the developer
  to work also swells the gelatin. Accelerating
  agents include sodium carbonate or sodium
  hydroxide.
• Prolonged exposure to these may result in
  dermatitis due to its alkalinity

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The Developer

• Preservative
• prevents oxidation of the developing agents by
  having a greater affinity for O2 than the
  developing agents themselves. The preservative
  used is sodium sulfite.
• Restrainer
• slows down the development rate in order to
  prevent fogging. Potassium bromide potassium
  iodine are the agents used.

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The Developer

• Dissolving Agent
• used is water.
• Hardening Agents
• used in automatic processors functions to
  prevent excessive emulsion swelling. These agents
  include gluteraldahyde.

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The Developer Replenisher

• In using the developer the bromide removed from
  the film builds up acts as a restrainer for
  prolonged developing time. Developer replenisher,
  which is a supercharged developer with no
  restrainer, can be added to the developer tank to
  bring the solution up to a proper level while
  also bringing it back to its proper strength.

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The Acid Stop-Bath

• This is absent in all automatic processors as the
  rollers within the processor function to squeeze
  off the developer.
• In manual developing, the acid stop-bath can be
  used after the film leaves the developer to stop
  the development immediately.

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The Acid Stop-Bath

• It is a weak acetic acid solution that
  neutralizes the alkaline developer.
• Acid stop-bath is not usually used because it
  necessitates having an extra tank. The film is
  usually rinsed in the water tank to remove most
  of the developer before putting it into the fixer.

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The Fixer

• Fixation involves two separate processes
• The clearing of the film of unexposed silver
  halide salts which are not affected by the
  developer which would turn black if exposed to
  light (these have not been reduced by the
  developer).
• The hardening of the emulsion.

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The Fixer

• The darkroom lights may be turned on as soon as
  the film has cleared since there are than no
  light sensitive elements in the emulsion.
• Clearing Agent
• removes the unexposed silver halide salts from
  the film (sodium thiosulfate, a.k.a. hypo). Most
  modern fixers use ammonium thiosulfate.

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The Fixer

• Hardener
• reduces the swelling softening of the emulsion
  produced by the alkaline developer hardens it
  (potassium alum).
• Preservative
• maintains proper acidity of the solution
  prevents early breakdown of the clearing agent
  (sodium sulfite).

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The Fixer

• Acidifier
• neutralizes the alkaline developer carried over
  keeps the medium acid for the hardener to do a
  full job (acetic or sulfuric acid).
• Dissolving Agent
• used is water.

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The Fixer

• In manual developing chrome alum may be used as a
  hardener instead of potassium alum.
• This makes the fixer opaque to light.
• Therefore, the lights may be turned on as soon as
  the film is put into the fixer with out harm.

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The Fixer Replenisher

• Replenisher for the fixer is available but care
  must be taken to remove enough of the old
  solution before adding the replenisher for
  solution carried out must be balanced by
  solutions carried in.

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Steps in Film Processing

• Before beginning to process film the developer
  fixer should be stirred with separate paddles.
• The temperature should be as close to 680 as
  possible.
• Developing times temperatures may vary.
• As a rule with increased temperature you decrease
  the developing time vice versa.

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Steps in Film Processing

• The film is removed from the cassette clipped
  into a film hanger.
• The cassette should be closed to avoid staining
  of the screens with solutions during processing.

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Steps in Film Processing

• The film is than passes through the following
  five steps (four with automatic processing)
• Developing
• Rinsing
• Fixing
• Washing
• Drying

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Steps in Film Processing

• Developing
• developing of the film may be done by
• 1) sight (under a safelight of course)
• 2) by time temperature charts which are
  available.
• The average time developing temp/time is 680 for
  5 minutes.

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Steps in Film Processing

• Time temperature is recommended because the
  opacity of the uncleared film the length of
  time for the eye to accommodate to the darkness
  makes inspection of the film difficult
  prolonged exposure to the safelight can fog the
  film.
• In either case the film should be agitated for
  the first few seconds in the developer to remove
  any air bubbles on the film surface that would
  restrict development in that area.

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Steps in Film Processing

• Rinsing
• After development the film should be rinsed in
  clear water (running) for 30 to 45 seconds to
  remove as much of the developing chemicals as
  possible to stop development prevent
  contamination of the fixer with alkaline
  developer.
• An acid stop-bath may be used in place of the
  rinse, but in using either the film should be
  drained before putting it into the fixer.
• In automatic processing the rinsing stage is
  removed

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Steps in Film Processing

• Fixing
• We have previously described the actions of the
  fixer as clearing hardening of the
  emulsion. These two processes occur
  simultaneously but the latter takes approximately
  twice as long.
• The clearing time is usually 3-4 minutes but the
  film is left in the fixer for 10 minutes for
  hardening.

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Steps in Film Processing

• Washing
• The finished film should be composed of metallic
  silver embedded in gelatin nothing else. The
  film must be thoroughly washed to remove all
  chemicals to prevent discoloration fading of
  the image.
• Films should be washed 15 minutes in clear
  running water, depending upon the rate of flow,
  temp., type of film used the type of fixer
  used.

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Steps in Film Processing

• The longer the film spends in the fixer, the
  longer the wash time needed.
• This is a 123 ratio of developer to fixer to
  wash.

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Steps in Film Processing

• Drying
• The ideal situation for drying of x-ray film is a
  film drying box that combines a heating element
  with a circulating fan. It can dry in 15 minutes.
• Film will dry properly if hung in air for a
  longer period (1 hours).
• A fan aimed at the edge of the film will speed up
  the process.

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Replenisher Method Exhaustion Method

• Both the developer the fixer may be either
  replenished to maintain the timing or used until
  exhausted by increasing the time element.
• Both methods are satisfactory but the replenisher
  method saves time, does not involve record
  keeping is less expensive.

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