processing the latent image dmi 50b kyle thornton
Post on 16-Jan-2016
217 Views
Preview:
TRANSCRIPT
Processing The Latent Image
DMI 50B
Kyle Thornton
Hand Processing
• Films were immersed in tanks containing processing chemicals for a period of time
• The chemicals had to be mixed and stirred by hand
• The total time was about an hour from developer to drying
• Occasionally, a film was read right out of the developer– Thus the term wet read
Automatic Processing• The first automatic processor still immersed film
in tanks– Films were hung, and a conveyor did the rest of the
work– It could process about 120 films/hour– Total time was about 40 minutes
• Eventually, the roller transport system was invented
• This is what is used today in automatic processors
Automated Processing 1940’s Style
An Updated Version
Advantages Of Automatic Processing
• Saves time and manpower
• Processing time is reduced to 90 seconds
• The variability in results caused by hand-dunking is eliminated
• Radiographs are available in minutes
• There is no variance in temperature
• Allows standardization of techniques
• Overall, efficiency is improved
Converting the Latent Image to a Manifest Image
• Step I– Formation of the latent image by exposing the
silver-halide grains to x-radiation
• Step II– Development of only the exposed grains by
reducing agents
• Step III– Removal of the unexposed grains and making the
image permanent by fixing
Latent Image Formation
The Sequence Of Processing Steps
• Wetting– Loosens the emulsion to allow penetration of
developing chemicals
• Development– The stage in which the latent image is converted
to a manifest image
• Stop Bath– An acid solution to stop the development process
The Sequence Of Processing Steps
• Fixing– Removes any silver halide crystals that were not
exposed to radiation or light
• Washing– Removes any chemicals not rinsed off in the
previous steps
• Drying– Removes any water, prepares the film for handling,
storage, and viewing
Sequence of Processing Steps
Wetting Solution
• Water– This is the solvent for all processing chemicals– A solvent is what solids and powders are mixed
into
• In automatic processing, this step is combined with development
Development
• The developer solution is a reducing agent
• It reduces the silver ions of exposed crystals to metallic silver
• The main development agent is hydroquinone– Rapidly produces shades of gray
• The other developing agent phenidone– Produces black tones slowly
The Effect of Development Upon Silver Halide Crystals
Exposure and ReductionOf Silver Halide Crystals
Underdevelopment v. Overdevelopment
Developer Chemicals and Their Functions
Fixing
• The stop bath is combined with fixing in the automatic processor
• Fixing stops the developing process and makes the manifest image permanent
• The activator that neutralizes any residual developer is acetic acid
• The other fixing agents remove any unexposed or undeveloped silver-halide crystals
Fixing Agents And Their Purpose
Hypo Retention
• Occurs when fixing solution (thiosulfate or hypo) is not rinsed sufficiently
• This will cause a processed film to discolor over time
• This is caused by oxidation of the fixing agent• The result is a discolored film of poor quality• This means that the wash cycle is not working
properly
Washing
• The agent in the washing cycle is water
• The film is rinsed to remove any chemical residue
• Water is continuously cycled through the wash tank to ensure that it remains clean
• Poor washing can result in hypo retention or other chemical artifacts
Drying
• The final step of the processing cycle
• Hot air is blown over the film to dry it
• The dryer stage works independently of the processing stages
Safety
• Developer chemicals are caustic and can cause chemical burns
• It will stain fabric permanently
• If chemicals are splashed on skin, or in eyes, rinse immediately, and seek treatment
• Protective eyewear, and aprons should be worn if mixing chemicals
Processor Anatomy
• Transport System
• Temperature Control System
• Circulation System
• Replenishment System
• Dryer System
• Electrical System
Processor Anatomy
Transport System
• A series of rollers moving in precision convey the film through each stage of development at precise intervals
• Begins at the feed tray
• A microswitch is placed here that detects the size film and controls replenishment
• The transport system consists of three subsystems
Subsystems• Rollers
– 1 inch diameter rollers that convey the film through the processor
• Transport racks
– All of the rollers are positioned on a rack assembly
– At each bend there is a curved metal lip called a guideshoe to properly position the film for turning
• Drive subsystem
– Supplied by a motor
– Drives the rollers and a series of gears, belts, and pulleys
Transport System Components
Temperature Control System
• Temperature, time, and chemical concentration control development
• Optimum temperature is app. 95 degrees F
• The temperature is monitored by a thermostat
• This controls a heating element in the developer tank
Circulation System
• Continuously agitates the processing chemicals ensuring that they are properly mixed
• Water is continuously circulated through the processor
Replenishment System
• Monitors film activity and replenishes the solutions as needed
• This prevents oxidation of the solutions in the processor
• A microswitch at the feeding tray monitors film size and regulates appropriate replenishment
Feeding Tray
Dryer System
• A blower sucks in room air and blows it across a heating element in order to dry film
• This also serves as exhaust for the automatic processor
Electrical System
• Supplies power to the processor
• Each electrical component of the processor has its own wiring and fuses
Rapid Processing
• Reduces processing time to about 30 seconds
• The chemicals are more concentrated
• Fixer and developer temperatures are higher
• Rapid processing is very useful in surgery, and emergency where time is valuable
Extended Processing
• Used in mammography
• Allows for lower patient dose
• Film is in the developer longer
• Processing time if about 3 minutes
• Contrast is improved
Daylight processing
• A processor is still used• The means of loading cassettes and putting
films is different• The daylight system allows automatic loading
of cassettes for use• Also automatically unloads them into the
processor• Eliminates time in the darkroom
Daylight Processing Unit
Dry Processing
• Does not use any wet chemicals• Two techniques for dry processing
– Photothermography• Laser light prints image• Formed on silver halide• Image developed by heat
– Thermography• Uses a heat source (print head)• Heat creates the image in organic silver salts
– Photothermography renders more accurate detail– Thermography can look pixely, and dust can accumulate between
print head and film
top related