Introduction
As we have previously known, X-rays are a modern and innovative technology used in medicine, especially in the field of medical diagnosis. One of the old methods of X-ray imaging is the use of X-ray film technology, which is an essential component that captures what is invisible and translates it into a visual representation such as internal body structures. X-ray film records information related to the body (tissues) through which X-rays pass, thus greatly helping in diagnosing and treating the patient's problem. In this article, we will learn about the X-ray film imaging technique used in medical diagnosis (development method), as well as a historical overview of it, the reactions that occur during imaging, the principle of film operation, and how we can choose the film.
History
The first X-rays were recorded on glass plates coated with emulsion on one side, requiring a high exposure dose. In 1839, Louis Daguerre discovered the phenomenon of development. The following year, it was found that treating exposed silver chloride paper with sodium chloride would make the image permanent. In 1914, nitrocellulose-based film, which was single-emulsion but highly flammable, was used for recording X-rays. Later, it was discovered that double-emulsion film responded to X-rays faster. By 1924, safety film made of cellulose triacetate replaced the nitrocellulose-based film.
X-ray Film
For X-ray photography, X-ray film usually consists of a gelatin emulsion containing radiation-sensitive silver halide crystals, such as silver bromide or silver chloride, and a flexible, transparent, blue-tinted base. Emulsion differs from emulsions used in other types of photographic film due to the distinct characteristics of gamma and X-ray, but X-ray film is sensitive to light.
In general, the emulsion is distributed in two parts in a layer about 0.0005 inches thick. By putting the emulsion on both sides of the head, the amount of silver halide radiation is doubled, thus increasing the speed of the film. Emulsion thin layers that are developing, fixing, and drying can be done in a reasonable amount of time. Some of the films used for radio have an emulsion on one side, which makes the main details of the image stand out.
Reaction of X-rays with Silver Halide
When X-rays, gamma rays, or light hit the grains of sensitive silver halide in the emulsion, some Br- ions are released and captured by Ag+ ions. This change is so subtle that it cannot be detected by conventional physical methods and is referred to as a "latent (hidden) image." Nevertheless, the exposed grains become more responsive to the reduction process when treated with a chemical developer, leading to the formation of black, metallic silver. This silver, suspended in the gelatin on both sides of the base, forms the image.
Principle of Working of X-ray Film
X-ray film operates on the principle of differential absorption of X-rays by different tissues and materials, combined with the photo-chemical reaction in the film. When an X-ray beam passes through the body, tissues of varying densities absorb X-rays to different extents. Dense tissues like bones absorb more X-rays, while less dense tissues like muscles and fat absorb fewer. The X-rays that pass through the body then strike the X-ray film, which consists of a base layer coated with a photosensitive emulsion containing silver halide crystals.
When the X-rays interact with the silver halide crystals in the emulsion, they cause a latent image to form. This latent image is invisible until the film is developed through a chemical process. The areas of the film that received more X-ray exposure become darker after development, as the silver halide crystals are reduced to metallic silver. Conversely, areas that received less exposure remain lighter. This results in a negative image on the film, where denser structures (like bones) appear white or light, and less dense structures (like soft tissues) appear darker.
The development process involves immersing the exposed film in a series of chemical baths. The developer solution reduces the exposed silver halide crystals to metallic silver, creating a visible image. The film is then rinsed to stop the development process, followed by immersion in a fixer solution to remove any unexposed silver halide crystals, ensuring the image is stable and permanent. Finally, the film is washed and dried. The end result is a detailed radiographic image that can be used by healthcare professionals to diagnose and assess various medical conditions.
- Note: The image recorded on the film is the result of exposure to X-ray photons.
Film Selection
The selection of a film when radiographing any particular component depends on a number of different factors. Listed below are some of the factors that must be considered when selecting a film and developing a radiographic technique:
- Composition, shape, and size of the part being examined and, in some cases, its weight and location.
- Type of radiation used, whether x-rays from an x-ray generator or gamma rays from a radioactive source.
- Kilovoltages available with the x-ray equipment or the intensity of the gamma radiation.
- Relative importance of high radiographic detail or quick and economical results.
Choosing the proper film and developing an optimal radiographic technique typically requires balancing various opposing factors. For instance, when high resolution and contrast sensitivity are paramount, a slower and finer-grained film is preferable to a faster film.
Conclusion
X-ray film technology has evolved significantly from its early use of glass plates to the advanced double-emulsion films utilized today. The development and operational principles of X-ray film revolve around the differential absorption of X-rays by various tissues, creating a latent image that is then developed into a visible radiograph through a series of chemical processes. The choice of film is crucial and depends on numerous factors such as the composition and size of the examined part, the type of radiation used, and the desired balance between image detail and processing efficiency. This intricate process enables healthcare professionals to diagnose and treat medical conditions effectively, demonstrating the enduring importance and sophistication of X-ray film technology in medical diagnostics.
Here (Part 1) of this topic ends, continue reading in (Part 2).
#xray #xray_film #medical_imaging #radiographic_film #radiography
