Radiographic Film

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Chapter 19

• Radiographic Film

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Radiographic Film

• Diagnostic radiographic film is manufactured by
  coating both sides of a base material with an
  emulsion containing photosensitive crystals.
• Several other materials are also used to improve
  the performance and permanence of the film
• Base
• Adhesive
• Emulsion with crystals
• Supercoat

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Film Base

• Originally composed of a glass plate.
• Cellulose nitrate once used but extremely
  flammable.
• Nonflammable cellulose triacetate introduced in
  1920s.
• Modern plastic bases (polyester introduced by
  DuPont in the 1960s) solve problems such as cut
  fingers from broken films and strained backs from
  carrying and filing stacks of heavy radiographs.

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Film Base

• Flexible yet tough
• Permit easy handling in the darkroom.
• Make good contact with cassette pressure pads.
• Stable
• Does not change its dimension during the heating
  and immersion in chemicals required for
  processing.
• Rigid
• To be placed onto viewbox.
• Uniformly lucent
• Permits transmission of light without adding
  artifacts to the diagnostic image.

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Reflections

• Crossover effect blurring of the image caused by
  light from one screen crossing into the light
  from another screen.
• Halation an effect on a radiographic image
  caused when light that is reflected from the air
  interfaces on the back of the base material.
• Antihalation coating a substance applied to the
  back of a single-emulsion film designed to absorb
  light coming from the emulsion and preventing
  backscatter, (removed by the processing chemicals
  to permit light to be transmitted through the
  film for viewing).

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Adhesive

• Designed to glue the emulsion to the base and
  prevent bubbles or other distortion when the film
  is bent during processing or handling, or when it
  is wet and heated during development.

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Emulsion

• Composed of gelatin in which photosensitive
  silver halide crystals are suspended.
• Acts as a nonreactive, neutral lucent suspension
  medium for the silver halide crystals (silver
  bromide, silver iodide, and silver chloride) that
  must be separated from one another to permit
  processing chemicals to reach them.
• Distributes the crystals evenly over the surface
  of the film- preventing clumps that would make
  one area of the film more photosensitive than
  another.

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Supercoat

• Layer of hard protective gelatin designed to
  prevent the soft emulsion from being abused
  physically or chemically.

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Manufacturing

• Radiographic film is manufactured in four stages
  
• Crystal production
• Ripening
• Mixing
• Coating

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Crystal Production

• AgNO3 KBr AgBr KNO3
• Gelatin must be present
• A medium to permit the crystals to form
• Limit oxidation and reduce crystal surface
  tension
• Facilitate other reactions
• Conventional grain
• Tabular grain
• Larger more evenly dispersed
• Absorption of a greater portion of the exposing
  photons
• Reduced light crossover from one emulsion to the
  other
• Reduced silver coating requirements

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Crystal Structure

• Structure permits both free silver atoms and free
  electrons to drift through the lattice- key to
  the formation of the latent image.
• Negatively charged surfaces
• Positively charged exteriors
• Sensitivity speck must be present to provide
  film sensitivity
• Serve as electrodes to attract the free silver
  ions
• Bromide serve as ion pumps to assist in the
  deposition of silver.

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Ripening

• Period during which silver halides are allowed to
  grow
• Size of the crystal determines their total
  sensitivity.
• At the proper time, emulsion is cooled, shredded,
  and washed to remove KNO3 (potassium nitrate)

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Mixing

• Colored dyes improve the sensitivity of the
  silver halides to match the wavelengths of
  photons that will be striking the emulsions
  during exposure.
• Panchromatic sensitive to al colors
• Orthochromatic not sensitive to the red spectrum
• Hardeners to prevent physical trauma
• Bactericides and fungicides
• Antifogging agents to decrease sensitivity to
  environmental factors, such as heat.

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Latent image formation

• The latent image is the unseen change in the
  atomic structure of the crystal lattice that
  results in the production of a visible image.

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Latent image formation
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Types Of Film

• Direct Exposure/ nonscreen films
• Intensifying screen films
• Special Application Films
• Mammography
• Detail extremity radiography
• Contact surgical radiography
• Cathode Ray Tube (CRT) imaging
• Laser Films
• Duplication Films
• Fluoroscopic spot filming

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Direct Exposure/ Nonscreen films

• Used primarily for industrial nondestructive
  testing (NDT) radiography.
• When extremely fine detail is critical to the
  diagnostic quality of the image (extremely high
  radiation exposure).
• Dental
• Reconstructive surgery of the hands
• Biopsy specimen
• Forensics
• Single emulsion, extremely fine grain silver
  halide crystals, much greater silver content.
• Thicker emulsion layer to achieve sufficient
  sensitivity- requires manual processing.

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Intensifying Screen Films

• Wide variety of speeds (controlled by the size of
  the crystals and the thickness of the emulsion),
  contrast ranges, latitudes, and resolutions.
• Larger crystals and thicker emulsions usually
  provide lower contrast, wider latitude, and less
  resolution.
• Double emulsion

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Special Application Films

• Fine grain films sensitive to a single screen
• Mammography x-ray examination of the breast
• Detail extremity radiography imaging that uses
  slower speed films
• Contact surgical radiography nonscreen film in
  sterilized packages
• Cathode Ray Tube (CRT) imaging Video imaging)
  requires a film that is sensitive to the light
  emitted by the CRT

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Special Application Films

• Lasers films directly exposed by the laser used
  in the imaging camera
• Film must be sensitive to the frequency of light
  emitted by the particular camera.
• Produces near distortion free images
• Duplication film designed to provide an exact
  image of the original film.
• Single emulsion
• Chemically fogged to D-Max further exposure
  decreases optical density (OD).
• Fluoroscopic spot filming imaging that is done
  with 70 mm roll film or 105 mm film chips that
  are sensitive to green light.

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Film Storage and Handling

• Film should be stored at a temperature of 68 F
  or lower at all times.
• Films must be brought to room temperature in
  advance of use.
• Humidity must be maintained between 30 and 60
  percent.
• Photosensitive materials must be protected from
  unfiltered light.
• Lead lining of storage area.
• Film should be stored on end.

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Film Identification

• Should be permanently identified with medical
  record information.
• Date of exposure
• Full name of patient
• Institution exposure made
• Referring physician
• Patient identification number
• Examination ordered