Computed Radiography (CR)
Film radiography is the oldest method of radiography which is still consider an excellent technology. High spatial resolution is the most important benefit of film radiography. Because of that, film radiography has important role in inspection of castings or forged metal parts–e.g., air foils, pumps, pump housings, gears, struts or landing gear components–where its sensitivity and high image resolution are particularly appropriate for identifying fine cracks or flaws that could lead to failure. Film radiography has some disadvantages, for example film inspection requires photographic development which is a potentially problematic, time-consuming process involving chemicals harmful to inspectors and the environment.
Computed radiography (CR) is potentially applicable in the same cases as film. It offers faster results without chemical processing. Instead of conventional film, a phosphor plate is substituted for the sheet of film Images [3]. Phosphor plates are read by a special laser scanner and image stored digitally for later review and archiving. Aerospace manufacturers must keep permanent records, thus this archiving method is valuable in aerospace applications. Some phosphor-plate readers can be situated conveniently in a van or truck. For mobile inspection operations this can be valuable and it reduces transportation capacity which is essential for on-site image examination. Because of more sensitivity and greater dynamic range of phosphor plates than film, CR also can reduce the exposure time needed to generate an image and this is a benefit which increases life of the X-ray source. Nowadays, because Current plate technology has some resolution limitations, film remains the preferred medium for critical, very high-resolution imaging [4]. It is noticeable that the new high resolution phosphor imaging plate introduced in recent years. This high resolution imaging plates can be used in the most high resolution application and can reach up to 25 micron spatial resolution.
A wide dynamic range in Computd radiography in comparition to film radiography
Advantage and disadvantage
CR image show a very dynamic range and good spatial resolution.However in very high resolution application, digital methods con not compete with conventional film radiography.
Considering contrast for conventional RT film,it is difficult to obtain the same quality radiograph in comparison with digital radiography system.considering the dynamic range, digital RT system show a very wide dynamic range in comparison with conventional film.
finally, it was shown that Computed radiography(CR) system has a complete superiority over the conventional film radiography system in dynamic range, contrast, signal to noise ration and crack detectability for the aerospace application.
A part o f Falcon-20 landing gear and its CR Image
a part of F-100 aircraft’s engine intake lip Used by CR and film radiography
