became a new clinical application as a new imaging method for exposures at the wall
stand, the Bucky table, and bedside imaging. The high technical requirements and
financial costs, associated with limited image quality and difficult handling—without
a reduction of examination time—delayed the transfer of storage phosphor
systems into routine clinical use, which started to increase at the beginning of the
1990s [4]. Today the storage-phosphor radiography systems or CR systems play a
fundamental role in the field of digital projection radiography. Other important
innovation was the development of flat-panel detectors in the middle of 1995.
Flat-panel detectors were initially developed to be integrated detectors in the
radiology equipment, but more recently they are available as nonintegrated detectors
and working as a wireless or a non-wireless technology.
Digital systems are traditionally split into two broadly defined categories [10, 11]:
computed radiography and digital radiography. Although this taxonomy is commonly
accepted other classifications are described [13]: direct digital radiography and indirect
digital radiography technologies (including CR). In this case the detector classification
is related with the conversion process of X-ray energy to electric charge. Figure 2.1
shows a schematic figure that includes a comparative diagram of the taxonomy of
digital radiography technologies, the conversion process, and the detector properties.
Other taxonomic option is to give a classification according to the integration of
the digital detector within the radiology equipment: in this case integrated and
nonintegrated detectors terminology could be used.
Despite the taxonomy that is used the major difference among digital technology
systems related with X-ray detection and readout process. Concerning CR systems
they use storage-phosphor image plates with a separate image readout process, which
means an indirect conversion process; DR technology converts X-rays into electrical
charges by means of a direct readout process using thin-film transistor (TFT) arrays.