Film Construction and Film Types
Before grasping the idea of film construction, it is important to note the concept of remnant radiation. The x- rays that interact with the x-ray film results to fewer original x-rays which come up with an image. The remnant radiation is typically the image-forming radiation that passes through the patient. Evidently, as a beam of x-rays strikes the body of the patient, they are attenuated by the patient; some of the x-rays are scattered while others are absorbed. The beams that hit the film are referred to remnant radiation, and they are useful (Gupta, 2014). The film is sandwiched in flanked by the radiographic intensifying screens in the protective cassette. The intensifying screens change the x-rays into the perceptible light. This light is responsible for exposing the radiographic film. Notably, its spectral response is unique from the common photographic film, but the mechanism of operation is similar.
The radiographic film has two essential parts; the base and the emulsion (see Appendix 1). Most films have two emulsions, hence, referred to as double emulsion film (Carlton & Adler, 2012). The emulsion is the crucial component of the film. A beam of x-rays interacts with the emulsion and transfers information to the film. The emulsion consists of a homogenous mixture of gelatin and silver halide crystals about 3µm -5µm. The primary function of gelatin is to provide a support medium for the silver halide crystals by holding them in place. Additionally, its porosity and transparency help it to transmit the light to the silver halide crystals. On the other hand, the silver halide crystals contain 98% of silver bromide and 2% of silver iodide. They are tabular shaped, about 1µm thick for film exposure. The interaction between the silver halide crystals and the photons produces a manifest image (latent image). Radiation interactions release the electrons; then the electrons migrate to the sensitivity center where the atomic silver is generated by attracting an interstitial silver ion. The process is repetitive causing a build-up of silver atoms. The remaining silver halide is then converted to silver during film construction. After the silver grain is formed, the non-radiated and the irradiated silver halide produces the latent image.
Types of Films
There are two
types of films. First, is the screen film that intensifies the
screens, since single emulsions use one screen. On the other hand, the non-screen-films or direct exposure film are used for duplication, cine, and dental (Carlton & Adler, 2012).
There are other special types of films; the mammography
film which has a single emulsion film and is conventionally used in modern radiography, the
laser film which is similar to laser
printers except that it is printed on a film and it is
mostly used in medical radiography. Additionally, there is the duplication film which has a single
emulsion, used to copy x-ray films. Also, there is the subtraction film which used in angiography to do subtraction where
the bone is removed which aids visibility
of arteries. Lastly, there is the spot
film and the Cine film. The spot
film is has a unique film of 70mm-105mm,
used in fluoroscopy and can be processed in x-ray film processor. The cine film
is a black and white film of 16mm-135mm and it is
used in coronary angiography.
Carlton, R. R., & Adler, A. M. (2012). Principles of radiographic imaging: an art and a science. New York: Cengage Learning.
Gupta, V. (2014). Radiodiagnosis and Imaging Services. Textbook of Hospital Administration , 145.
White, S. C., & Pharoah, M. J. (2014). Oral radiology: principles and interpretation. Elsevier Health Sciences.