processing

• Fixing


  The process of clearing the silver halide that was not exposed to radiation from the emulsion and hardening the emulsion to preserve the image
• Developing, fixing & washing


  Important steps in the processing of radiographic film
• Automatic Processing


  1. Wetting

  2. Developing

  3. Stop Bath

  4. Fixing

  5. Washing

  6. Drying
• Automatic film processors


  • 1942: First automatic film processor introduced by Pako, processing rate 120 films/hr, dry-to-drop time 40 mins
  • 1956: First roller transport system processor introduced by Eastman Kodak, dry-to-drop time 6 mins
  • 1965: 90-second rapid automatic film processor introduced by Eastman Kodak, dry-to-drop time 90 secs
  • 1987: 45-second automatic film processor introduced by Konika, requires special films & chemicals
• Dry-to-drop time

  Manual: 70 mins & 45 s, Automatic: 90 s
• Wetting

  1. Purpose: swells the emulsion to permit subsequent chemical penetration

  2. Manual: 15 s, Automatic: included in the developing
• Developing


  1. Purpose: produces a visible image from the latent image

  2. Manual: 5 mins, Automatic: 22 s
• Stop Bath

  1. Purpose: terminates development and removes excess chemical from the emulsion

  2. Manual: 30 s, Automatic: included in the fixing
• Fixing


  1. Purpose: removes remaining silver halide from emulsion and hardens gelatin

  2. Manual: 15 mins, Automatic: 22 s
• Washing


  1. Purpose: removes excess chemicals

  2. Manual: 20 mins, Automatic: 20 s
• Drying


  1. Purpose: removes water and prepares radiograph for viewing

  2. Manual: 30 mins, Automatic: 26 s
• Wetting agent

  Water, purpose: swell the gelatin to allow chemicals to penetrate the emulsion
• Solvent


  A liquid into which various solids and powder can be dissolved, water is the universal solvent
• Developing


  Principal action: to change the silver ions of exposed crystals into metallic silver
• Reduction to metallic silver

  Ag+ + e- -> Ag
• Synergism occurs when action of two agents working together is greater than the sum of the action of each agent working independently
• Lack of sufficient glutaraldehyde may be the biggest cause of problems with automatic processing
• Redox reactions


  Reduction: process by which an electron is given up by a chemical to neutralize a positive ion, Oxidation: reaction that produces electron
• Components of the developer

  • Developing agent
  • Activator/Buffering agent
  • Restrainer
  • Preservative
  • Hardener
  • Sequestering agent
  • Solvent
• Developing agent


  Primary component: Hydroquinone, Secondary components: Phenidone & Metol
• Activator/Buffering agent


  Chemicals: Sodium carbonate & Sodium hydroxide, helps swell gelatin, produces alkalinity, controls pH
• Restrainer


  Chemicals: Potassium bromide & Potassium iodide, antifog agent, protects unexposed crystals from chemical attack, prevents development fog
• Preservative


  Chemical: Sodium sulfite, controls oxidation, maintains balance among developer components
• Aerial oxidation


  Occurs when air is introduced into the developer after it is mixed, handled & stored, close-fitting floating lids control it, oxidized developer is brownish, hydroquinone is sensitive to it
• Hardener


  Chemical: Gluteraldehyde, controls emulsion swelling, enhances archival quality
• Depletion of glutaraldehyde is the usual cause of damp film that is dropped from the processor
• Archival quality


  The permanence of the radiograph, the image does not deteriorate with age but remains in its original state
• Sequestering agent


  Chemicals: Chelates, remove metallic impurities, stabilize developing agent
• Solvent


  Chemical: Water, dissolves chemicals for use
• Film development


  Basically a chemical reaction, three physical characteristics: time, temperature and concentration of developer
• Unexposed silver halide crystal

  Has a negative electric charge distributed over its entire surface
• Exposed silver halide crystal

  Has a negative electric charge distributed over its surface, except at the sensitivity center
• Underdevelopment


  Appearance: dull radiograph, the crystals that contain a latent image have not been completely reduced
• Overdevelopment


  Appearance: dull radiograph, partial reduction of unexposed crystals
• Proper development


  Appearance: maximum contrast
• Factors affecting development


  • Crystal size
  • Developer concentration
  • Developer temperature
• Development fog


  Causes: increased in developer time, temperature and concentration
• Chemical fog


  Cause: chemical contamination of the developer
• Radiation fog


  Causes: unintentional exposure to radiation or by improper storage at elevated temperature and humidity
• Fixing


  Principal action: to treat the film so that the image will not fade but will remain permanently (archival quality)