About radiography films
Radiography films are primarily made up of two things;
Base: Base is a transparent, flexible blue tinted object, usually made from a clear and flexible plastic such as cellulose acetate. It provides physical support to emulsion and does not participate in the image-forming process. It is not sensitive to radiation, nor can it record an image.
Emulsion: Emulsion consists of gelatin which consists of radiation sensitive silver halide crystals such as silver bromide & Chloride. Emulsion is coated on both sides of the base in layers about 0.0005 inches thick. Due to the emulsion coating on both sides of the base, the amount of radiation-sensitive silver halide gets doubled & hence it increases the film speed.
Development of radiography films
Once a film has been exposed to sufficient amount of radiation, it captures the latent image. Now we need to chemically develop the film to convert the captured latent image to a visible image for the purpose of interpretation. To convert an exposed film (latent image) to an useful radiograph (visible image), following steps are followed;
- Stop bath
Development: It is the initial step converting the latent image to a useful and readable image. Film is exposed to the developer solution. Developer makes the latent image visible. Main function of developer is to reducing (or eliminate) the exposed silver bromide crystals to black metallic silver. Developing the film is multi-step process. The developer solution contains chemicals comprised of alkali and metol or hydroquinone mixed with water. Alkali present in the development solution, penetrates the protective coating and allows the metol to reduce the exposed silver bromide to black metallic oxide.
Stop Bath: It is the second step in the processing of films. Function of stop bath is to quickly neutralize any excessive development of silver crystals. Since over development of the silver crystals may result in a radiographic image that is virtually impossible to interpret. This bath is comprised of a glacial acetic acid and water.
Fixing: Fixing (or fixer) is the third step followed in the development of a film. Fixer permanently fixes the image on the film. It is due to this process that the the radiographic image is preserved over a periods of time.
Fixing (or fixer) is also a multi-step process. The fixer removes any unexposed silver crystals and then hardens the remaining crystals in the emulsion.
Washing: Once the film has been properly developed, it is then rinsed in water to remove all the unwanted chemicals
Drying: Film is then left for drying. After drying, the film is ready for interpretation.
Interpretation is usually done with the help of a viewer. A viewer is a small box having sufficient light, upon which the film is kept and analyzed.