Selection of look-up tables (LUT) in digital imaging also affects contrast. Images having long-scale contrast will have a wide exposure latitude that is, the radiographer will be able to utilize a broader range of technical factors to produce a diagnostic-quality image.Ĭontrast is determined by the kilovoltage (kV energy/quality/penetrability) of the x-ray beam and the tissue composition of the body part being radiographed. Images having a short-scale of contrast will have narrow exposure latitude. Exposure latitude is the range of exposures over which the recording medium (image receptor) will respond with a diagnostically useful density in other words, this is the "flexibility" or "leeway" that a radiographer has when setting his/her exposure factors. Low contrast, or long-scale contrast, means there is much gray on the radiograph, and there are many gray shades between black and white.Ĭlosely related to radiographic contrast is the concept of exposure latitude. High contrast, or short-scale contrast, means there is little gray on the radiograph, and there are fewer gray shades between black and white. The range between black and white on the final radiograph.
#DIRECT EXPOSURE X RAY FILM SOFTWARE#
The brightness of the radiograph in digital imaging is determined by computer software and the monitor on which the image is being viewed.Ĭontrast is defined as the difference in radiographic density between adjacent portions of the image. With digital imaging, however, density may be referred to as brightness. A higher radiographic density represents more opaque areas of the film, and lower density more transparent areas of the film. Density is a logarithmic unit that describes the ratio between light hitting the film and light being transmitted through the film. Radiographic density is the measure of overall darkening of the image. This is why bone, which is very dense, process as being ‘white’ on radio graphs, and the lungs, which contain mostly air and is the least dense, shows up as ‘black’. Conversely, areas on the image receptor that receive the least radiation (portions of the remnant beam experience the most attenuation) will be less exposed and will be processed as being lighter. Areas on the image receptor that receive the most radiation (portions of the remnant beam experiencing the least attenuation) will be more heavily exposed, and therefore will be processed as being darker. The remnant beam is responsible for exposing the image receptor. What remains of the primary beam after attenuation is known as the remnant beam. Anatomy that is denser has a higher rate of attenuation than anatomy that is less dense, so bone will absorb more x-rays than soft tissue. When the primary beam passes through the body, some of the radiation is absorbed in a process known as attenuation. When an exposure is made, x-ray radiation exits the tube as what is known as the primary beam. X-rays are a form of ionizing radiation, meaning it has sufficient energy to potentially remove electrons from an atom, thus giving it a charge and making it an ion. Projectional radiography relies on the characteristics of x-ray radiation ( quantity and quality of the beam) and knowledge of how it interacts with human tissue to create diagnostic images. Therefore, indirect-exposure films without intensifying screens should not be used for intraoral radiography.Lead is the main material used by radiography personnel for shielding against scattered X-rays. Their speed and contrast would have been increased if intensifying screens had been used. In general, the indirect-exposure films had lower speed, lower contrast and wider latitude than the direct-exposure films. The direct-exposure films Hanshin Hi-Fi and Hanshin New Silver were equivalent in speed, higher in contrast, and narrower in latitude than Kodak Ektaspeed film. Therefore, they should not be used for intraoral radiography because they needlessly expose the patient to excessive X-ray radiation. Indirect-exposure films without intensifying screens were extremely slow compared with direct-exposure "E" and "D" speed films. The characteristic curves of Kodak Ektaspeed ("E" speed) and Ultra-speed ("D" speed) films were used as standards for comparison. The purpose of the present investigation was to determine whether film speed, inherent contrast, and latitude of Japanese indirect-exposure films used without intensifying screens were comparable to those of direct-exposure (non-screen) films used for intraoral radiography. In Japan, some dentists use indirect-exposure (screen) films for intraoral radiography, without the use of intensifying screens.