8/8/2023 0 Comments Fast emulsion film![]() ![]() Backing: Another gelatin layer sometimes used to prevent curl, inhibit light piping, and improve image quality or to act as a filter to make the film insensitive to certain wavelengths.Base support: The material that forms the structural support onto which the other sensitive and protective layers are coated.Subcoat: A very thin coating that ensures adherence of the emulsion to the base support.Emulsion: The light-sensitive layer, made up of silver halide suspension in a high-grade gelatin support.Overcoat: A protective layer that aids in scratch protection both before and after processing.The layers of an x-ray film ( Figure 2-1) and their functions are as follows: Combinations of different-sized crystals are used to create the desired characteristic curve, a measurement that describes the relationship between radiographic exposure and optical density. It naturally follows that the larger the silver halide crystal, the faster the speed of the film and the less the exposure. Generally speaking, the film’s inherent speed depends on the silver halide crystal (grain) size, structure, and sensitivity the choice of developer and the time and temperature that the film is processed. In medical radiography, many products have been designed to offer a vast array of speed levels and contrasts appropriate for the body part being radiographed. Scratches, for example, will permanently damage the screen. Exercise extreme care not to touch the screen except when cleaning. A drop of chemical could stain or damage the screen before it is wiped off. Do not spray the formula directly onto the screen spray onto a cloth first. Screen cleaners often contain an antistatic solution. They should be cleaned as recommended by the manufacturer. If they are cared for properly and not accidentally damaged, intensifying screens can last many years. They have, therefore, widely replaced calcium tungstate systems. ![]() Rare-earth intensifying screens are faster than calcium tungstate film/screen systems and do not sacrifice resolution. Incorrect matching of the film and screen will result in a slower film/screen system speed, which means using a longer exposure technique. Green-sensitive (orthochromatic) film must be used with green-emitting intensifying screens and blue-sensitive film with blue-emitting intensifying screens. Calcium tungstate screens emit light in the blue/blue–violet portion of the visible light spectrum rare-earth screens primarily emit green light, although a few emit blue light. Two types of intensifying screens are available: calcium tungstate and rare earth. Intensifying screen selection traits include its speed and, more importantly, spectral qualities. This allows the exposure technique to be reduced, which reduces patient exposure to x-radiation. Because radiographic film is sensitive to light, fewer x-rays are needed to expose the film. Intensifying screens are composed of light-emitting phosphors that fluoresce when exposed to x-rays. The intensifying screen is primarily responsible for making radiographic imaging a relatively safe medical diagnostic tool. Because x-radiation is absorbed by tissue (and accumulated), any method to reduce dosage and yet provide a usable image is desirable. X-rays are extremely inefficient in producing optical density (blackening) of the radiographic film. The typical image receptor used in film–screen radiography consists of a radiographic film that is sandwiched between two intensifying screens, all protected in a container known as a cassette.Ībout 99% of the exposure on radiographic film comes from the light emitted by the intensifying screen. The radiographic film is processed with chemicals to produce a visible (manifest) image, which is then viewed on a light box, catalogued, and physically stored. X-rays, after passing through the patient, interact with the image receptor, and a latent image (an invisible change that represents the object that was radiographed) forms in the film. WILLIAMSONįor over 100 years, radiography has used some form of film/intensifying screen combination as an image receptor. ![]()
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