FILM SCREEN - MANUAL & AUTOMATIC PROCESSING

FILM-SCREEN IMAGE ACQUISITION, PROCESSING AND IMAGE ANALYSIS

Latent Image

The invisible image that is induced in the silver halide crystal

Manifest Image

The image that exists on film after processing

Black metallic silver

Purpose of processing:

• Change silver halide crystals from film emulsion (after exposure to x-ray or light photons) to ___________.

Visible image

Purpose of processing:

• Latent image (invisible until processed) is developed into a __________

Poor diagnostic quality

Purpose of processing:

• Improper or careless processing can cause _________

Pako Company

• First to introduce automatic processor in 1942

• Could process 120 films per hour with the use of special film hangers.

• The total cycle time for processing one film was approximately 40 minutes.

Eastman Kodak Company

In 1956,

• Introduced the first roller transport system for processing medical radiographs

• 6-minute processing time

In 1965,

• Introduction of 90-second rapid processing

Rapid processing

• Was possible because of the development of new chemistry and emulsions, as well as the faster drying permitted by a polyester film base.

• With this processor, the dry-to-drop time is 90 seconds.

1. Wetting

2. Developing

3. Rinsing

4. Fixing

5. Washing

6. Drying

Manual Processing steps include

1. Developing

2. Fixing

3. Washing

4. Drying

Automatic Processing inlcudes:

Wetting

• 1st step in manual processing

• Swells the emulsion so that subsequent chemical baths can reach all parts of the emulsion uniformly

• In automatic processing, this step is omitted because the wetting agent is incorporated into the second step, developing.

Developing

• 2nd step in manual processing

• The stage of processing during which the latent image is converted to a visible image.

• Very short and highly critical

Rinsing

• 3rd step in manual processing

• After developing, the film is rinsed in an acid solution designed to stop the developing process and remove excess developer chemicals from the emulsion.

• Photographers call this step the stop bath.

Fixing

• 4th step in manual processing

• The process of clearing unexposed silver halide crystals from the emulsion and hardening the emulsion to preserve the image.

• The gelatin portion of the emulsion is hardened at the same time to increase its structural soundness.

• Stage of processing where when development is complete, the film must be treated so that the image will not fade

Washing

• 5th step in Manual Processing

• This removes any remaining chemicals from the previous processing steps.

Drying

• 6th step in Manual Processing

• This removes the water used to wash it and to make the film acceptable for handling and viewing.

Processing Chemistry

The chemicals used to process films are designed to penetrate an emulsion and cause an effect.

Developing, fixing, and washing

___________ are important steps in the processing of radiographic film.

Wetting agent

In wetting, for these chemicals to penetrate the emulsion, the radiograph must first be treated by a _________.

Water

Wetting agent is ______.

• This penetrates the gelatin causing it to swell.

Developer

In automatic processing, the wetting agent is in the _________.

Development

• The chemical process that amplifies the latent image.

• Changes the silver ions of exposed crystals into metallic silver

  • The developer provides electrons to the sensitivity center of the crystal to change the silver ions to silver.

• For the ionic silver to be changed to metallic silver, an electron must be supplied to the silver ion.

Developer

The ________ provides electrons to the sensitivity center of the crystal to change the silver ions to silver.

Electron

For the ionic silver to be changed to metallic silver, an _________ must be supplied to the silver ion.

Reduction

Process when an electron is given up by a chemical, in this case the developer, to neutralize a positive ion

Oxidation

• The opposite of reduction

• A reaction that produces an electron

Redox reactions

Oxidation and reduction occur simultaneously and are called ________

Reducing agents

Reduce exposed silver halide to black metallic silver

Hydroquinone

• Acts rather slowly but is responsible for the very blackest shades.

• The principal component of the developer

Phenidone

Acts rapidly and influences the lighter shades of gray.

Synergism

Occurs when the action of two agents working together is greater than the sum of the action of each agent working independently.

Ex: Phenidone and Hydroquinone

Buffering Agents

• Enhance the action of the developing agent by controlling the concentration of hydrogen ions: the pH

• very corrosive and can cause a skin burn

  • Ex: Sodium carbonate and Sodium hydroxide (Lye)

Sodium carbonate

Component: Activator/ Buffering agent

Function: Helps swell gelatin; produces alkalinity; controls pH

Chemical: ?

Restrainers

Restrict the action of the developing agent to only those silver halide crystals that have been irradiated will be reduced.

• Ex: Potassium bromide and potassium iodide

Potassium bromide

Component: Restrainer

Function: Antifog agent; protects unexposed crystals from chemical “attack”

Chemical: ?

Preservative

• Control the oxidation of the developing agent by air (aerial oxidation)

• By controlling aerial oxidation, the _________ helps maintain the proper development rate

  • Ex: Sodium sulfite

Hardener

• Controls swelling and softening of the emulsion.

• When films that drop from the processor are damp, the usual cause is depletion of the ________.

• Lack of sufficient glutaraldehyde may be the biggest cause of problems with automatic processing.

  • Ex: Glutaraldehyde

Glutaraldehyde

• Lack of sufficient __________ may be the biggest cause of problems with automatic processing.

• Controls emulsion swelling and enhances archival quality

Sequestering agents

Form stable complexes with these metallic ions and salts

• Ex: Chelates

Chelates

Are introduced as sequestering agents that form stable complexes with these metallic ions and salts.

Film development

Is basically a chemical reaction

• With proper development, all exposed crystals that contain a latent image are reduced to metallic silver, and unexposed crystals are unaffected

1. Time,

2. Temperature, and

3. Concentration (of the developer)

Film development is governed by three physical characteristics:

Long development time

Increases reduction of the silver in each grain and promotes the development of the total number of grains.

• High developer temperature has the same effect.

Development fog

• An increase in any of these factors (time, temperature, and developer concentration) beyond manufacturer recommendations results in increased __________

• If developing is not stopped, ____________ results

Chemical fog

Fog also can be produced by chemical contamination of the developer (_________), unintentional exposure to radiation (radiation fog), or improper storage at an elevated temperature and humidity

Radiation fog

Fog also can be produced by chemical contamination of the developer (chemical fog), unintentional exposure to radiation (____________), or improper storage at an elevated temperature and humidity

Archival quality

• The image is said to be fixed on the film, and this produces film of _______________

• Refers to the permanence of the radiograph:

  • The image does not deteriorate with age but remains fixed.

Trapped

When the film is removed from the developer, some developer is _________ in the emulsion and continues its reducing action.

Stop bath

• Step in manual processing that follows development

• Function is to neutralize the residual developer in the emulsion and stop its action.

  • The chemical used is acetic acid.

Acetic acid

• In manual processing, The chemical used in the stop bath is ___________.

• In automatic processing, the fixer contains _________ that behaves as a stop bath.

Activator

• In automatic processing, a stop bath is not used because the rollers of the transport system squeeze the film clean.

• Furthermore, the fixer contains acetic acid that behaves as a stop bath.

• This acetic acid, however, is called an __________

• Neutralizes the pH of the emulsion and stops developer action.

Fixing agents

• The terms clearing agent, hypo, and thiosulfate often are used interchangeably in reference to this.

• Remove unexposed and undeveloped silver halide crystals from the emulsion.

Sodium thiosulfate

The agent classically known as hypo, but ammonium thiosulfate is the fixing agent that is used in most fixer chemistries

Ammonium thiosulfate

• ___________ is the fixing agent that is used in most fixer chemistries.

• Component: Fixing agent

• Function: Removes undeveloped silver bromine from emulsion

• Chemical: ?

Hypo retention

Is the term used to describe the undesirable retention of the fixer in the emulsion.

Excess hypo

Slowly oxidizes and causes the image to discolor to brown over a long time.

Yellow-brown

Fixing agents retained in the emulsion combine with silver to form silver sulfide, which appears _________.

Silver sulfide stain

Is the most common cause of poor archival quality.

Hardener

• The fixer also contains a chemical called a ___________.

  • As the developed and unreduced silver bromide is removed from the emulsion during fixation, the emulsion shrinks.

• Accelerates this shrinking process and causes the emulsion to become more rigid or hardened.

• Their purpose is to:

  • Ensure that the film is transported properly through the wash-and-dry section and that

  • Rapid and complete drying occurs

• The chemicals commonly used are:

  • Potassium alum, aluminum chloride, and chromium alum

• Normally, only one is used in a given formulation.

Potassium alum

• Component: Hardener

• Function: Stiffens and shrinks emulsion

• Chemical: ?

Preservative

• The fixer also contains a ___________ that is of the same composition and that serves the same purpose as the preservative in the developer

• The _________ is sodium sulfite

• Needed to maintain the chemical balance because of the carryover of developer and fixer from one tank to another

Sodium sulfite

• Component: Preservative

• Function: Maintains chemical balance

• Chemical: ?

Buffer

• The alkalinity and acidity—the pH—of the fixer must remain constant.

• This is helped by adding a _________, usually acetate, to the fixer.

Solvent

• Finally, the fixer contains water as the ________.

  • Other chemicals might be applicable as a ________, but they are thicker and are more likely to gum up the transport mechanism of the automatic processor.

• Dissolves other components

Washing/ wash

• The next stage in processing is to _________ away any residual chemicals remaining in the emulsion, particularly hypo, that clings to the surface of the film

• Water is used as the _______ agent.

3°C (5°F)

In automatic processing, the temperature of the wash water should be maintained at approximately _________ below the developer temperature.

• In this way the wash bath also serves to stabilize developer temperature.

Inadequate washing

Leads to excessive hypo retention and the production of an image that will

fade, turn brown with time, and be of generally poor archival quality.

Three-step process

Converting the latent image to a visible image requires a ______-step process.

Drying

• Final step in processing

• Warm dry air is blown over both surfaces of the film as it is transported through the drying chamber.

1 hour

The total sequence of events involved in manual processing takes longer than _________ to be completed.

90-second processors

Most automatic processors are ____________ and require a total time from start to finish—the dry-to-drop time—of just that, 90 seconds.

• Transport system

• Temperature control system

• Circulation system

• Replenishment system

• Dryer system

The principal components of an automatic processor are the:

Transport system

• Transports film through various stages at precise intervals

• The ___________ begins at the:

  1. Feed tray, where the film to be processed is inserted into the automatic processor.

  2. Entrance rollers grip the film to begin its trip through the processor

  3. Microswitch is engaged to control the replenishment rate of the processing chemicals.

• Not only transports the film; it also controls processing by controlling the time the film is immersed in each wet chemical.

Alternate sides from film to film

Always feed the film evenly using the side rails of the feed tray and _________.

• This ensures even wear of the transport system components

Receiving bin

From the entrance rollers, the film is transported by rollers and racks through the wet chemistry tanks and the drying chamber and is finally deposited in the ___________.

Side rail

The shorter dimension of the film should always be against the _________, so the proper replenishment rate is maintained.

• Rollers,

• Transport racks, and

• Drive motor

The transport system consists of the following three principal subsystems:

• Transport rollers

• Master rollers

• Planetary rollers

Three types of rollers are used in the transport system

Transport rollers

• With a diameter of 1 inch, convey the film along its path.

• They are positioned opposite one another in pairs or are offset from one another

Master roller

With a diameter of 75 mm (3 inches), is used when the film makes a turn in the processor

Planetary rollers

A number of ________ and metal or plastic guide shoes are usually positioned around the master roller

Guide shoes

A curved metal lip with smooth grooves guides the film around the bend.

Crossover rack

• When the film exits the top of the rack assembly, it is guided to the adjacent rack assembly through a _____________.

• A smaller rack assembly that is composed of rollers and guide shoes.

Drive motor

Power for the transport system is provided by a fractional horsepower ___________.

Temperature Control System

• The developer temperature is most critical, and it is usually maintained at 35°C (95°F).

• Wash water is maintained at 3°C (5°F) lower.

35°C (95°F)

The developer temperature is most critical, and it is usually maintained at___________.

• Wash water is maintained at 3°C (5°F) lower.

Temperature

Is monitored at each stage by a thermocouple or thermistor and is controlled thermostatically by a controlled heating element in each tank.

Circulation System

Continuously pumps the developer and the fixer, thus maintaining constant agitation

Agitation

• Necessary to:

  • Continually mix the processing chemicals,

  • Maintain a constant temperature throughout the processing tank, and

  • Aid exposure of the emulsion to the chemicals.

Filtration

• __________ in the fixer circulation system is normally unnecessary because the fixer hardens and shrinks the gelatin so that the rollers are not coated.

• Developer

• Traps particles as small as approximately 100 µm to trap flecks of gelatin that are dislodged from the emulsion.

12 l/min (3 gal/min)

Fresh tap water is piped into the tank at the bottom and overflows out the top, where it is collected and discharged directly to the sewer system.

• The minimum flow rate for the wash tank in most processors is ___________.

Replenishment system

Meters the proper quantities of chemicals into each tank to maintain volume and chemical activity.

60 to 70 mL

Replenishment rates are approximately ______ of developer and 100 to 110 mL of fixer for every 35 cm (14 in) of film.

100 to 110 mL

Replenishment rates are approximately 60 to 70 mL of developer and ___________ of fixer for every 35 cm (14 in) of film.

• Volume replenishment

• Flood replenishment (timed or standby replenishment)

Types of Replenishment system

Volume replenishment

• Most common type

• Controlled by the size of the film (microswitch)

• Chemicals are replenished for each size of the film

Flood replenishment (timed or standby replenishment)

• Processors that are not in constant use

• Controlled by a timer

Drying system

• consists of:

  • Blower,

  • Ventilation ducts,

  • Drying tubes, and

  • Exhaust system.

• Extracts all residual moisture from the processed radiograph, so it drops into the receiving bin dry.

Depletion of glutaraldehyde,

Most processing faults leading to damp film are because of _____________, the hardener in the developer.

2500 W capacity

In drying system, sometimes as many as three heating coils of approximately _________ are used