Radiographic recording

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Radiographic recording

• Film Materials

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Film groups

• X-ray films
• Films exposed to X-radiation alone (Direct
  exposure film)
• Films exposed to x-radiation and light (Screen
  type film)
• (these are usually of double sided emulsion)
• Films exposed to light only. E.g. fluorographic
  films, duplicating films, Cine films
• (these are of single sided emulsion)

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Film structure
Double sided emulsion
Single sided emulsion
Base
Base
Super coat Emulsion Substratum Anti halation/curl
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Film base

• Polyester made from polyethlene terepthalate
  resin is used now
• It is extremely strong and untearable
• Demonstrate high dimensional stability
• Cellulose triacetate was used before

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Functions of film base

• To provide a support for the emulsion layer
• To transmit light so that an image can be viewed

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Desirable characteristics of film base

1. Transparent, free from any defect, uniform
   transmission of light
2. Strong but flexible to
3. Withstand mechanical stress during processing and
   handling
4. be made thinner to minimize parallax (0.18 mm
   for sheet film, 0.08 for roll film)
5. Uniform in thickness
6. Dimensionally stable during processing

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Desirable characteristics of film base

1. Impermeable to water or processing solutions
2. Non- flammable
3. Chemically inactive
4. Uniform in colour, if a colour tone is added
   during manufacture

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The subbing layer / adhesive layer

• This is required,
• To ensure that emulsion layer adheres to the
  smooth and shiny base during manufacture
• To prevent any separation of the emulsion layer
  from the base during processing
• A mixture of gelatin solution and solvent of the
  film base is used

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The emulsion layer

• This is a layer of silver halide suspended in
  gelatin
• It is coated on the subbing layer
• The shape of crystals is important , it affects
  the sensitivity of the film and the sharpness of
  the image
• Kodak is pioneer in producing flat grain emulsion
• Light absorbing magenta dye is added to the
  surface of the grains to increase the sensitivity
  and to absorb the irradiating light within the
  emulsion so that unsharpness produce by that way
  is reduced

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The supercoat

• This is a thin layer of gelatin which is applied
  to the emulsion
• The prime functions are
• To protect the emulsion from the effect of
  pressure or abrasion.
• To provide suitable surface characteristics
  sufficiently glossy to reduce accumulation of
  dust not too glossy as to prevent the grip by
  the rollers of processor.

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Non-curl backing

• Present only in single emulsion sheet film.
• Function is to prevent the tendency of the film
  to curl when the emulsion swells during
  processing.
• This is a gelatin layer coated on a subbing layer
• It swells equally as the emulsion layer and
  counteract the swelling of emulsion on the other
  side.

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Anti-halation layer

• When a colour dye is added to the anti-curl layer
  to prevent the effect of halation, it is called
  an anti-halation layer

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Halation ?

• The ghost image produced out side the proper
  image, by the light transmitted through the base
  and reflected back from the base-air interface is
  called halation.

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Halation
Light from screen
emulsion
base
True image
Halation
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Prevention of Crossover effect

• Crossover effect is a type of halation occur when
  using double sided emulsion films with two
  intensifying screens.
• I.e. The light from one screen crosses the base
  and produces a ghost image on the opposite
  emulsion
• To prevent this a colour dye (magenta for green
  sensitive films) is added to the surface of the
  emulsion.
• The dye has the effect of reducing the light
  scattering within the emulsion and, at the same
  time limiting crossover and thus image unsharpness

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Irradiation

• This is the sideways scattering of light within
  the emulsion itself as a result of the light
  striking the grains of silver halide
• This light contributes nothing to the image
  proper but becomes a source of image unsharpness.
• The use of thin emulsion layers produce less
  irradiation.

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Films for medical imaging

• Duplitized emulsion films
• Direct exposure films - Dental x-ray films,
  Radiation-monitoring films
• Screen type films used with two intensifying
  screens- General radiography films
• Single emulsion films
• Screen type film used with single screen
• Photofluorography films - Cine film, 70mm 105
  mm roll film, 100 mm sheet film
• Cathode ray tube (CRT) photography films
• Duplication films
• Subtraction films
• Laser imaging films

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End