CR (Computed Radiography) is the digital replacement of conventional film-based radiography.

CR technology is based on the fact that certain atoms can "store" x-ray energy.  The stimulable phosphor plate, which uses the same material as the image intensifier screens in film cassettes, is used instead of film.  A CR plate is enclosed in a cassette, which is the same size as conventional film cassettes. 

The major advantage of this technology is that existing film-based x-ray systems can be upgraded by merely exchanging the cassettes.  A plate is exposed, the image information is captured, and a laser scanner then reads the plate by measuring the light energy that is being released.  After flooding the plate with an intense light source to make sure that there is no latent energy left, the plate is ready for reuse.  In principle, the plate can be used indefinitely.