![]() ![]() It is critical to use blue-sensitive film with blue light–emitting screens and green-sensitive film with green light–emitting screens. In radiography, two categories of spectral emission generally exist: blue light–emitting screens and green light–emitting screens. Spectral emission refers to the color of light produced by a particular intensifying screen. When radiographic film is used with intensifying screens, it is important to match the spectral sensitivity of the film with the spectral emission of the screens. ![]() In radiography, there are generally two categories of spectral sensitivity films: blue-sensitive and green-sensitive (orthochromatic). Spectral sensitivity refers to the color of light to which a particular film is most sensitive. The bromine liberated by x-ray or light exposure is neutral and is simply absorbed into the gelatin of the emulsion. The more x-ray or light exposure in a particular area of the film, the more electrons and silver available to be attracted to the sensitivity specks. Every silver ion that is attracted to an electron becomes neutralized by that electron, therefore becoming metallic silver ( 6). Therefore these sensitivity specks become negatively charged ( 4).īecause the sensitivity specks are negatively charged, the positive silver ions that are liberated from the AgBr molecules are attracted to them ( 5). Each sensitivity speck serves as an electron trap, trapping the electrons lost by the bromine when x-ray or light exposure occurs. These imperfections are called sensitivity specks. Physical imperfections in the lattice or architecture of the AgBr crystals occur during the film manufacturing process. If enough energy is absorbed by a particular AgBr molecule, it becomes a positive ion of silver, neutral bromine, and a free electron ( 2, 3). This energy absorption raises the conductivity level of the electrons in the AgBr molecules, and these electrons move faster as a result. Energy in the form of x-rays or light is absorbed by the emulsion layers of radiographic film. The silver in AgBr is in effect an ion because it shares only its outer-shell electron with bromine. This electron is shared through ionic bonding because silver is a transitional atom, having only one electron in its outer shell, and it tends to either lose it or share it. ![]() Silver (Ag) and bromine (Br) are bound together as a molecule in such a way that they share an electron ( 1). The process by which the latent image is formed is precisely the same for silver iodide as it is for silver bromide. However, because silver bromide (AgBr) is the primary constituent of the silver halide in the emulsion layer of film, only silver bromide is discussed. ![]() Silver halide is made up of both silver bromide and silver iodide. Most film used in radiographic procedures has a blue dye or tint added to the base layer to decrease eye strain when viewed on a view (illuminator) box.īOX 12-2 The Gurney-Mott Theory of Latent Image Formation The emulsion layer is fairly fragile and must have a layer composed of a polyester base so that the film can be handled and processed, yet remain physically strong after processing. Silver halide is the material that is sensitive to radiation and light. The emulsion of film consists of silver halide crystals suspended in gelatin. The emulsion layer is the radiation-sensitive and light-sensitive layer of the film. The most important layer for creating the image is the emulsion layer. The composition of film can be described in layers ( Box 12-1). Depending on the specific application, film manufacturers produce film in a variety of sizes ranging from 20 × 25 cm (8 × 10 inches) to 35 × 43 cm (14 × 17 inches). Several types of radiographic film are still used in medical imaging departments. As a result, film serves as the medium for image acquisition, processing, and display. Radiographic film acquires the image and must then be chemically processed before it is visible. Picture Archiving and Communication System (PACS) Digital Imaging and Communications in Medicine (DICOM) ![]()
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