Chapter 20

1. Chapter 20 Film Processing

2. 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

3. 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

4. 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.

5. 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.

6. 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

7. 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

8. 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

9. 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.

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

11. Fixing:Clearing 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.

12. Fixing:Activator / 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

13. Fixing:Hardener • 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.

14. Archiving:Washing / 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.

15. Automatic Processing:Transport 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

16. Automatic Processing:Transport 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.

17. Automatic Processing:Dryer 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

18. Automatic Processing:Replenishment 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.

19. Automatic Processing:Replenishment 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

20. Automatic Processing:Circulation 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.

21. Automatic Processing:Temperature 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.

22. 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

23. 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.