Breakthroughs in Radiography: Computed Radiography

CE Email comments/questions to [email protected], fax 800-556-3288, or log on to www.VetLearn.com Computed radiography (CR) is a digital imaging technology and digital x-ray image management system that has been used in human and veterinary medicine since the 1980s. CR helps eliminate many of the disadvantages of traditional radiography. A storage phosphor plate collects the pattern of x-ray attenuation that is extracted by a reader, which converts the data into a digital signal. The image is stored like any computer file and can be viewed on a computer screen, transmitted electronically, or printed out on paper or transparent film, similar to x-ray film. Computer software allows manipulation of the digital image to enhance viewing. which means that it cannot tolerate a wide range in radiation exposure without risking saturation. In some studies, that latitude limitation means some areas will be overexposed and some underexposed in the same film. In general, users must choose between good contrast and good latitude with traditional radiography1 (Figure 1). Another disadvantage with traditional radiography is that the image cannot be adjusted once taken. Although some errors, such as positioning problems or patient movement, reduce image quality regardless of the technology, other errors have different remedies depending on the procedure used. With traditional radiography, the film is exposed and then processed and viewed. At that time, any errors in the exposure cannot be remedied. Therefore, the image must be retaken, which increases radiation exposure to the technician and patient, increases the cost of the examination, inconveniences the animal’s owner, and uses additional technician and veterinarian time. In addition, traditional radiography requires handling of film for viewing, archiving, and January 2004 1 COMPENDIUM Reprinted with permission by Veterinary Learning Systems. COMPENDIUM January 2004 Breakthroughs in Radiography: Computed Radiography 2 CE Figure 1. Comparison of a conventional film-screen radiograph and a CR film. (Courtesy of Dr. Kip Berry, Maitland, FL) Conventional pelvic radiograph of a dog with a total right-hip prosthesis. CR film of the same patient. Increased resolution of the fine bony trabeculae and increased edge sharpness of the bony and soft tissue structures are apparent. Note the resolution of the wire mesh of the acetabular prosthesis compared with the image at the left. transmission to others. If a pet owner, horse owner, or another veterinarian wishes to view an image from a remote location, the image must be either copied and sent via courier or scanned before electronic transmission. Films must be stored in a physical space that is large enough to access and sort films. This is usually a separate area from the patient’s other records. HISTORY OF DIGITAL RADIOGRAPHY CR is a digital imaging technology introduced in human medicine in the 1980s by Fujifilm Medical Systems. CR is a process, not a single product. It is an entire digital x-ray image management system. Its use in veterinary medicine has increased over the last decade as smaller, more affordable systems have become available. Mobile equine practitioners have been the leaders in the use of CR technology because of its advantages for mobile farm calls. Digital radiography is used for both small and large animal imaging, in veterinary teaching hospitals, by specialists (including veterinary dentistry), and in large private practices. As its use increases and prices drop, more practices will use digital radiography. TECHNOLOGY OF COMPUTED RADIOGRAPHY CR is an indirect capture digital imaging technology, which means that plates are used to capture the image before it is transferred to a computer. CR systems for veterinary medicine use a hospital’s current radiographic generator. The image is created on reusable storage phosphor imaging plates rather than film. The storage phosphor plates are similar to intensifying screens. When exposed to x-rays, intensifying screens emit light immediately, exposing the radiographic film. In contrast, when phosphor plates are exposed to x-rays, part of the radiation energy is absorbed by electrons, which store the image temporarily. The latent image is read by scanning the imaging