Film Processing

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Chapter 20

• Film Processing

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Film Processing

• The primary purpose of radiographic processing is
  to deposit enough black metallic silver at the
  latent image sites to permit a permanent visible
  image to form.
• Four steps
• Developing
• Fixing
• Washing
• Drying

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Developing

• Silver is deposited at the latent image sites and
  an image becomes visible.
• The deposition of silver amplifies the density of
  the image.
• The action of the developer is controlled by the
  immersion time, solution temperature and chemical
  activity.
• Primary agents of the developer
• Reducing agents
• Activator
• Restrainer
• Preservative
• Hardener
• Water- solvent

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Developer Reducing agents

• Phenidone (P developer) quickly reduces silver,
  enhancing fine detail and subtle shades of gray
  and works only in areas of light exposure.
• Hydroquinone slowly reduces silver and produces
  heavy density.
• Superadditivity when two agents are combined,
  ability greater than the sum of independent
  ability.

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Developer Reducing agents

• The process of reducing agents giving up
  electrons to neutralize the positive silver ions
  at the sensitivity speck to become black metallic
  silver.
• Provide electrons to the silver ions attached to
  the sensitivity specks of the silver halide
  crystals (the latent image).
• Saturated speck opens gate to allow electrons in
• When silver obtains electron converted into black
  metallic silver
• Negative exterior of crystal prohibits the
  reducing agent from supplying electrons to the
  silver ions because the bromine and iodine repel
  electrons.
• More exposure more silver saturation larger
  gate faster reduction more black metallic
  silver.
• Produces a film with varying degrees of blackness.

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Developer Reducing agents

• Chemical fog the effect on the film when
  unexposed silver halides are reduced
• Reducing agents permitted to work too long or
• Too fast due to high temperature

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Developer Activator / Restrainer

• Activator
• Sodium carbonate
• Maintains developer in alkaline solution.
• Assists the reducers in reaching the silver
  halides by causing the gelatin to swell and
  become more permeable.
• Restrainer
• Potassium bromide
• Restrict the reducing agents action to those
  crystals with sensitivity speck gates.
• Permits overactive reducers to attack it, instead
  of unexposed silver halides.
• Antifogging agent

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Developer Preservative / Hardener

• Preservative
• Sodium sulfite
• Decrease oxidation of the reducing agents
• Hardener
• Glutaraldehyde
• Controls the swelling of the gelatin to prevent
  scratches and abrasions to the emulsion during
  processing
• Maintains uniform film thickness to assist in
  transport though an automatic processor

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Developer Contamination

• As little as 0.1 percent fixer from adjacent tank
  into the developer will destroy the ability of
  the reducing agents.
• Films appear gray- extremely low contrast.

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Fixing

• Removes undeveloped silver halides from the
  emulsion to permanently fix the image before
  exposure to light for viewing.
• Primary agent clearing agent

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FixingClearing Agent

• Clearing agent
• Ammonium thiosulfate
• Bonds with the unexposed silver halides and
  removes them from the emulsion.
• Uses silver in the emulsion to form ammonium
  thiosilversulfate.
• When fixer is given insufficient time to remove
  unexposed silver halides- milky appearance
  appears
• Clearing time twice the time necessary for the
  milky appearance present) to disappear.

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FixingActivator / Preservative

• Activator
• Acetic acid
• Provides acidic pH to enhance functioning of
  clearing agent
• Stops reduction (reducing agents function in
  alkaline solution)
• Preservative
• Sodium sulfite- same as developer
• Dissolves silver from the ammonium
  thiosilversulfate.
• Maintains pH

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FixingHardener

• Hardener
• Potassium alum
• Controls the swelling of the gelatin to prevent
  scratches and abrasions to the emulsion during
  processing.
• Maintains uniform film thickness to assist in
  transport though an automatic processor.
• Insufficient hardener will cause films to exit
  the processor with moist softened surfaces.

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ArchivingWashing / Drying

• Archiving prepares the film for long term storage
  as a medical record by protecting it from
  deterioration by chemical, fading, and physical
  forces.
• Washing uses water to remove developing and
  fixing chemicals.
• Drying uses hot air to evaporate water and
  harden/seal emulsion.

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Automatic ProcessingTransport System

• Designed to move a film through the developer,
  fixer, wash and dryer sections of the processor.
• Controls the length of time the radiograph is
  immersed in each of the solutions and agitates
  the chemistry to ensure maximum reaction.
• Subsystems
• Transport racks
• Crossover networks
• Drive system

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Automatic ProcessingTransport System

• Transport racks move the film down into and up
  out of solution tanks
• Crossover networks turn the film down into the
  next tank.
• Entrance rollers designed to start the film
  traveling from the feed tray down into the
  developer section
• Films should always be fed with the short axis
  along the feed tray guide.
• Drive system turn rollers
• Speed controls the time the film is immersed in
  each chemical.

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Automatic ProcessingDryer System

• Begins with a series of squeegee crossover
  rollers removing excess wash water from the
  surface of the film
• Then driven between hot air tubes
• Film emulsion shrinks and seals dry

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Automatic ProcessingReplenishment System

• Replaces chemicals that are depleted through the
  chemical reactions of processing, oxidation, and
  evaporation.
• Starter solution acetic acid and potassium
  bromide added to the replenisher solution when
  starting a fresh tank of developer.
• Potassium bromide needed to develop films
  properly
• Initial source is from emulsion on films. A newly
  mixed tank does not have, must be added.

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Automatic ProcessingReplenishment System

• Volume replenishment- high volume units
• Activated when films enter the processor
• Flood replenishment- low volume units
• Automatically floods the developer and fixer
  tanks with replenisher solutions at a regular
  interval regardless of the number of films
  processed

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Automatic ProcessingCirculation System

• Designed to stabilize temperatures, agitate
  solutions, mix the chemistry, and filter the
  solutions.
• Constant mild agitation is required so the
  chemicals will enter and exit the emulsion.
• Fresh chemicals added by replenishment systems
  need to be agitated to avoid overdevelopment,
  underdevelopment, and under fixation.

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Automatic ProcessingTemperature Control System

• Heat exchanger uses a thermostat to heat the
  developer, developer then routed through
  circulation coil in the bottom of fixer and wash
  tanks.
• Developer temperature critical, change of 0.5 is
  noticable.

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Darkroom

• Safelights film is designed to be insensitive to
  orange-red light. Amount of this light controlled
  by type of filter, wattage of light source,
  distance from working surface
• Entrance single door, double interlocking doors,
  revolving doors and light proof mazes.
• Pass box light proof container set in darkroom
  wall for delivery of film cassettes.
• Ventilation to vent hazardous fumes

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Silver Recovery Systems

• Operate by providing electrons that can be used
  by the silver in the fixer solution to form black
  metallic silver.
• Metallic Replacement fixer acid breaks down the
  iron in a steel screen or in steel wool and
  displaces it with silver.
• Iron oxide gives up electrons for silver
• Low volume situations
• Electrolytic passes a current from a cathode to
  an anode through the fixer, the ionized silver is
  attracted to the negatively charged cathode.
• Moderate to high volumes
• Chemical Precipitation uses chemicals to break
  down in the fixer and release electrons, the
  silver is heavy and falls to the bottom of the
  tank.
• Resin uses acid to form resin ions, the silver
  is attracted to the resin, the resin is processed
  to remove the silver.