From where will you retrieve your film when it exits the automatic processor?

• State the importance of film identification, and list the several methods of film identification available

• State the recommended criteria for filing a radiograph

GLOSSARY

Accelerators: Chemicals that increase the pH of the developer and subsequently increase the rate of developing.

Acidifiers: Compounds that accelerate the fixing process and neutralize the alkaline developer.

Buffers: Compounds in the fixer that maintain proper solution pH.

Clearing agents: Also called fixing agents; a portion of the fixer that dissolves and removes the unexposed silver halide crystals from the film emulsion.

Developer: A chemical solution that converts the latent image on a film to a visible image by converting the exposed silver halide crystals to black metallic silver.

Developing agents: Chemical solutions used to convert a latent image on x-ray film to a visible image.

Fixation: The process by which the unexposed silver halide crystals are removed from the film and the gelatin is hardened.

Fixer: The chemical solution used during fixation.

Hardeners: Chemicals added to the fixing solution or to developers in automatic processors to prevent excessive emulsion swelling.

Latent image: An invisible image on unprocessed x-ray film after it has been exposed to ionizing radiation or light.

Preservatives: Chemicals that prevent rapid decomposition of the developer or fixer.

Restrainers: Often potassium bromide and potassium iodide are used as restrainers or antifoggants. Restrainers limit the action of the developing agent to the exposed silver bromide crystals in the film.

Reticulation: A darkroom artifact produced by variable chemical temperatures that cause irregular expansion and contraction of the film emulsion, resulting in a mottled density appearance.

Rinse bath: A solution (usually water) used to remove excess developer solution before the film is placed in the fix tank.

Solvent: Water; dissolves the ingredients of the developer or fixer and diffuses the chemical into the emulsion of the film.

Stop bath: A solution of acetic acid and water used to “stop” the development of the x-ray film by rapidly neutralizing the alkaline developer solution.

INTRODUCTION

Proper film processing is vital to the production of a quality radiograph. Many believe that the use of appropriate exposure factors is the only component necessary to produce a “good” film. This is far from the truth. The production of a good-quality radiograph depends on many factors, one of which is film processing. When manual processing was the norm in human hospitals, it was said that 90% of all poor-quality radiographs were the result of poor processing. This is still relevant in veterinary radiography. One goal of the radiographer is to eliminate all possible pitfalls that may inhibit quality. A common area for pitfalls is the darkroom. Although quality does not begin in the darkroom, it could possibly end there.

The basic principles of radiographic processing have remained the same over the years, but technology has made remarkable advances toward automation. However, although an increasing number of veterinary practices use automatic film processing, the majority still process radiographs by hand with tanks to hold the processing chemicals. Both methods of processing are discussed in detail in this chapter.

THE DARKROOM

Three qualities constitute a good darkroom. A darkroom must be (1) clean, (2) organized, and (3) lightproof. Although individual darkrooms may vary in design, all should possess the same qualities. A darkroom should be separate from the radiographic suite and should be used for only one purpose: processing exposed radiographs. Ideally, the room dimensions should be no less than 6 × 8 feet (2.6 × 2 m), and the layout should reduce the possibility of film damage. Most of the work in the darkroom is performed with minimal illumination. Therefore it is important that the darkroom be organized so that all of the equipment can be located quickly and easily. And, of course, cleanliness is crucial. This is the only room where both the intensifying screens and the x-ray film are exposed to the air. If the countertops are dirty and soiled with chemicals, it is easy for both to be sucked into the cassette as it is opened, possibly causing damage to the intensifying screens.

Another factor that is often overlooked in the darkroom is climate control. Because the film emulsion is extremely sensitive to heat and humidity, good ventilation and temperature control are mandatory. A darkroom should be relatively cool and should have low humidity. The specific temperatures and humidity for proper film care are described in Chapter 6.

Organization

There should be essentially two sides to the darkroom: a dry side and a wet side (Fig. 7-1).

Figure 7-1 A sample dark room layout showing a wet side and a dry side.

Dry side.

The dry side of the darkroom is where the cassettes are unloaded and reloaded. A countertop or tabletop large enough to accommodate the largest cassette in the open position should be available. The tabletop should be constructed of a material that allows frequent cleaning, which is necessary to reduce the source of darkroom artifacts that can potentially get on the film. It must be impossible for chemicals to splash into the dry side. At no time should anything “wet” be brought to the dry side. It is customary to store film under the dry table, either in a cupboard or in a film bin, to allow easy access for reloading cassettes (Fig. 7-2). Film hangers for each size of film should be hung above the table on the dry side on an appropriate bracket. Brackets can be purchased commerially or constructed inexpensively using large hooks found at any hardware store.

Figure 7-2 Film storage bin. When closed, the film is stored light-tight in a vertical position.

Film hangers are available in two designs: channel hangers and clip hangers (Fig. 7-3). Channel hangers tend to retain water and chemicals and need special cleaning and drying to prevent contamination of the dry side. Films must also be removed from the channel hangers to be dried. However, clip hangers are more fragile than the channel type. When the clips are used frequently over a period of time, they become weak and lose the ability to “stretch” the film. The clips also puncture the four corners of the film, which, when filed, can scratch other films in the same envelope. It is important to cut off the corners of films processed with clip hangers before filing to prevent this. When more than one film is processed at the same time in the tanks, the clips on the hangers can scratch neighboring films.

Figure 7-3 A clip film hanger (left) versus a channel film hanger (right).

Wet side.

The wet side of the darkroom is where the actual chemical processing is performed. A darkroom that hand processes films usually consists of three tanks containing developer, water, and fix solutions. Various tank designs are available. The three tanks can be individually freestanding and warmed as required by an immersion heater (placed in the developer). Alternatively, the developer and fix tanks can be placed in one large tank filled with thermostatically controlled water. The latter system is preferred and can be purchased as a complete package constructed with 3- or 5-gallon (9- or 22-L) individual tanks. The water tank is usually four times the size of the smaller developer and fix tanks. The central water tank should have a circulating water system to provide a way to regulate temperature and rinse chemicals off the films during the processing procedure. A thermometer is an essential piece of equipment for the processing tanks because radiographic film is developed for a specified time on the basis of the temperature of the chemicals.

The wet side should also have a film-drying area consisting of either a drying rack or a drying cabinet. The drying rack should be placed in a dust-free area to prevent artifacts from sticking to the wet films. A drying cabinet is a heated forced-air unit that hastens the drying process. A viewing screen is also recommended on the wet side to evaluate radiographs. A “wet” film can be viewed, and, if a second radiograph is required, the radiographer can immediately evaluate the error. This is best achieved in the darkroom before too much time has elapsed.

Darkroom Lightproofing

As mentioned earlier, one criterion of a good darkroom is that it be lightproof. Light leaks in a darkroom can cause significant film fog; therefore taking appropriate measures to lightproof the darkroom is imperative. Lightproofing a room is more difficult than may be expected. The first step is locating the light leaks. Small light leaks may not be perceptible until the eyes have acclimated to the dark, and it may be necessary to spend 5 minutes waiting for the eyes to adapt. To achieve a truly lightproof room, a number of tasks may be necessary.

The entrance to the darkroom is a common site for light leaks. A double-door system or revolving door is preferred but not always practical in a veterinary practice (Fig. 7-4). The first step in lightproofing a standard door is to fit it tightly into its frame against strips of felt or rubber molding. Weather stripping is also useful around doors to prevent the entrance of light. Light entering from underneath the door can be prevented by a vapor seal designed specifically for the bottom of a door. A sliding bolt lock or doorknob lock prevents someone from accidentally entering the darkroom at an inopportune time. A suspended ceiling can be a radiographer’s nightmare. It may be necessary to place a large black sheet of plastic above the ceiling tiles to prevent light in adjacent rooms from entering through the seams.

Figure 7-4 A revolving door for the darkroom. This door is an effective means of entering and exiting the darkroom without risking exposure of the film to light.

It is a common fallacy that the walls of a darkroom should be “dark.” The opposite is true. The walls of the darkroom should be painted white or cream with a good-quality, washable paint. By painting the walls a light color, more reflection of the safelight is produced, providing a more visible work environment. If the quality and intensity of the light are “safe,” the illumination reflected from any surface also is “safe,” regardless of the color of that surface.

Darkroom safelight.

Correct safe lighting in the darkroom is crucial. A “safe” light means that the light produced will not affect the film. Radiographic film is sensitive to ultraviolet light. Safelights use a small-wattage bulb and a special filter to eliminate the light from the blue and green spectrum. The light bulb should be 15 watts or less. The filter varies by manufacturer. The most common types are a brown filter (Wratten 6B, Kodak) for blue-light-sensitive film and a dark-red filter (Wratten 6BR or GS-1) for green-light-sensitive film. The dark-red filter is recommended because of its versatility: both green-light- and blue-light-sensitive film can be used in this lighting.

Safelights should be positioned so that darkroom work can be performed without fumbling. There are two types of safe lighting: direct and indirect (Fig. 7-5). Direct lighting is a diffused light that shines directly over a work area such as the dry or wet side of the darkroom. Indirect lighting is a filtered light directed toward the ceiling and reflected over the entire room. Indirect lighting is often combined with direct lighting. At no time should the safelight be closer than 4 feet from a work area. A safelight that is too close, has a too-high wattage bulb, or has incorrect filtration may cause film fog.

Figure 7-5 Indirect (left) and direct (right) safe lighting for the darkroom.

The efficiency of a safelight can be tested; this is discussed in Chapter 10. Remember, no light is “safe” if the film is exposed to it for a prolonged period. Therefore the film bin should be open only when removing or replacing film. Fogging will result even with a safelight if the bin is left open or if film is left on the counter.

FILM-PROCESSING SOLUTIONS

Film processing, whether it is manual or automatic, comprises five basic steps: (1) developing, (2) rinsing or stop bath, (3) fixing, (4) washing, and (5) drying. The first step in learning how to process a film is a basic understanding of the processing solutions. The chemical solutions can be purchased in a number of forms. Powders and liquid concentrates are those most commonly used in veterinary practice. Water is added to the concentrates according to the manufacturer’s instructions to produce the proper amount of solutions for the processing tanks. Preparing the chemicals correctly is important or the resulting solution may adversely affect the radiographic product.

Every effort should be made to keep the chemical solutions at a specified temperature—any variance may adversely affect the radiographic product. At temperatures below those recommended, some of the chemicals may become sluggish in action and may produce an underdeveloped or underfixed radiograph. At temperatures much above those recommended, the chemical activity is too high for manual control.

Keep in mind also that all of the chemical solutions should be the same temperature. If the chemicals vary greatly in temperature, film reticulation can result. Reticulation appears as a mottled density on a finished radiograph and is caused by irregular expansion and contraction of the film emulsion.

A quality assurance program should be established and maintained in the veterinary practice. This program allows reproducibility, and it gives the radiographer confidence in the exposures used on each radiograph (see Chapter 10).

The Developer

The developer is a chemical solution that converts the latent image on a film to a visible image. The primary function of the developer is to convert the exposed silver halide crystals to black metallic silver.

The developing time usually is specified by the chemical manufacturer. Keep in mind that the developer temperature affects the developing time. Time-temperature developing is preferred over visual inspection when using the manual processing technique. This manual inspection is called “sight developing,” which consists of increasing or decreasing the time according to visual inspection of film density while the film is still in the tank. This technique requires attention and skill and is often subject to error. Sight developing should be avoided if at all possible.

The developer consists of developing agents, accelerators, preservatives, restrainers, hardeners, and a solvent.

1. Developing agents are composed of chemical compounds such as hydroquinone or phenidone that can convert exposed grains of silver halide to black metallic silver. The developing agent has little or no effect on the unexposed silver halide crystals.

2. Accelerators are chemicals that increase the activity of the developer. Substances such as potassium carbonate or sodium carbonate are used to increase the pH to an alkaline range of 9.8 to 11.4. This increase in pH causes the emulsion to swell and soften, allowing the developing agent to work more effectively.

3. Preservatives prevent the rapid oxidation that can occur with alkaline developing agents. They also help maintain a stable development rate and prevent staining of the emulsion layer.

4. Restrainers limit the action of the developing agent to the exposed silver bromide crystals in the film.

5. Hardeners are often added to developers in automatic processors. They harden the film during processing and prevent excessive swelling of the emulsion. If the gelatin emulsion were to swell extensively, it could be damaged by the rollers in the automatic processor.

When processing film in an automatic processor What is the proper order of steps for the solutions?

During which step of automatic film processing are the unexposed silver halide crystals removed from the film base?

In which stage of automatic film process will the latent image be converted to the manifest image?

What happens when a film is placed in developing solution?