Conventional radiographs are formed by variations in the optical density of photographic emulsion on a flexible film base. They must be viewed using a radiographic view box, can be large and heavy, require a great deal of storage space and are prone to being damaged or lost. In contrast, digital radiographs exist only as computer files. Probably the biggest advantage of digital radiography is that it enables radiographic images to be stored digitally, readily retrieved for review and transmitted instantly between colleagues. Digital radiographs (and other imaging studies) can be linked to other parts of an electronic patient record, which facilitates search and review of clinical case material. Other potential advantages include lower running costs, no need for a darkroom, higher patient throughput, the greater dynamic range of digital detectors and the possibility to reduce X-ray exposure to the patient. Processing of digital radiographs is used to improve image quality by reducing noise, removing technical artefacts and optimising contrast for viewing. Most digital radiography systems are readily incorporated into practices because they can be used with the existing X-ray machine. In the future, all radiography will be digital.

Techniques for creating digital radiographs can be divided into computed radiography (CR) and direct radiography (DR). This terminology is potentially confusing, but it is intended to distinguish CR systems, which use storage-phosphor image plates that are exposed and then undergo a separate image readout process, from DR systems, which convert X-rays into electrical charges more or less directly, enabling almost instantaneous readout. In CR the storage-phosphor image plate is usually contained in a cassette that resembles the cassettes used for film-screen radiography. After exposure, the readout and digital processing steps of CR take a similar amount of time as processing conventional film. The quality of CR images is variable depending on the specifications of the system used and technical factors such as exposure and processing. Many CR systems require X-ray exposures comparable to those used with a 200 speed film-screen system and produce images with greater latitude but lower resolution.

DR systems use a variety of methods to produce radiographic images. Portable, flat-panel detectors are increasingly popular. These contain either a photoconductor/thin-film transistor array or a scintillator/photodiode/thin-film transistor array to capture X-rays and provide the readout. These detectors are directly wired to the user interface and produce images that can be viewed within a few seconds of exposure. Studies requiring multiple views or perfect patient positioning can be obtained efficiently with such systems. Compared to conventional radiography and CR, DR systems are able to produce better quality images at lower X-ray exposures. With some DR systems, it is unnecessary to use a grid.

Probably the biggest disadvantage of digital radiography is the cost of replacing existing radiographic equipment. Other potential disadvantages include greater technical complexity and the need to learn new radiographic methods and artefacts, which may be difficult for seasoned practitioners with ingrained radiography habits.

References

1.  Cesar LJ, Schueler BA, et al. Artefacts found in computed radiography. British Journal of Radiology 2001; 74: 195-202.

2.  Körner M, Weber CH, et al. Advances in digital radiography: physical principles and system overview. RadioGraphics 2007; 27: 675-686.

3.  Ludwig K, Schulke C, et al. Detection of subtle undisplaced rib fractures in a porcine model: radiation dose requirement-digital flat-panel versus screen-film and storage-phosphor systems. Radiology 2003; 227: 163-168.

4.  http://animalinsides.com/