Lesson 2

• Protect the emulsion from damage

  Overcoat
• heart of the x-ray film

  emulsion
• Allows the emulsion and base to maintain proper contact and integrity

  Adhesive layer
• what the um thick of the emulsion

  3-5 um think
• foundation of the x-ray film

  base
• x-ray film um think

  150-300
• (world war 1) – first x-ray film base

  Glass plate
• flammable

  cellulose nitrate
• safety base

  cellulose triacetate
• – resistant to warping and stronger than polyester

  polyester
• what is the um think of the polyester

  175 um think
• Primary purpose is to provide a rigid structure onto which the emulsion can be coated

  Has uniform lucency

  Film base
• maintains the size and shape of the x-ray film

  dimensional stability
• reduces eye strain and fatigue

  blue dye
• The material in which the light photons from the I.S interacts

  Emulsion
• Consist of a gelatine and silver halide crystals

  Clear and porous 


  emulsion
• Provides mechanical support for silver halide crystal

  Gelatine
• AgBr

  98%
• AgI

  2%
• Silver Z


  47
• Bromine Z


  35
• Iodine Z

  53
• what are the type of silver halide crystal (structure)

  tabular

  cubic

  octahedral

  irregular
• Photoelectron and silver ions combine to form the

  Latent image
• Chemical contaminant (silver sulfide)

  Introduced by chemical sensitization

  Sensitivity center
• Number of sensitivity center per

  crystal

  Concentration of crystals in the emulsion

  Size and distribution of cystals 


  Factors affecting the performance characteristic of the film
• ________ contain thicker emulsion with more silver halide crystal

  direct exposure films
• Type of radiographic film

  screen film

  direct exposure film

  mammography film
• a type of film which is used with an intensifying screen

  Characteristics of screen film:

  Contrast Speed , Crossover, Spectral matching, Anti crossover, or anti halation dyes safelight

  Screen film
• _____ is inversely proportional to latitude

  Contrast
• _____ has smaller and uniform grains

  High contrast emulsion
• ______ has larger grains and has wider range of sizes

  Low contrast emulsion
• Is the sensitivity of screen film to light

  Speed
• efficient use of silver in the emulsion (use of tabular grains)

  Covering power
• For direct-exposure film, speed is principally a function of the

  concentration and the total number of silver halide crystals.
• Silver halide grain sizeSilver halide concentration

  screen film
• Is the exposure of an emulsion caused by light from the opposite radiographic intensifying screen

  Crossover
• Tabular grain emulsion =

  Higher covering power
• It absorbs more of the crossover light

  Does not diffused in the emulsion but remains as separate layer

  Completely removed during processing

  Characteristic of crossover layer
• Light emission from the IS should match the colour sensitivity of the film

  Spectral matching