Content area
Full Text
Digital radiography detector systems were first implemented for medical applications in the mid 1980s, but the promise of digital imaging was not realized until the early 1990s, in conjunction with the establishment of first generation picture archiving and communications systems (PACS). At the time, there was only one technology available to replace the analog screen-film detector-a cassette-based, passive acquisition photostimulable storage phosphor (PSP) and plate reader system, known as "computed radiography" (CR). This system closely emulated the screen-film paradigm. Alternate technologies for digital image acquisition appeared in the mid 1990s with the use of large field of view (FOV) Xray phosphors and optical lens assemblies to focus the X-ray induced light output onto a small-area charge coupled device (CCD) photodetector array, as well as rectangular CCD arrays used with slot-scan geometries. Activematrix flat-panel imager (AMFPI) systems ap-peared in the late 1990s and early 2000s, employing either an X-rayto- light converter with photodiode array, or a semiconductor material to directly convert incident X-rays into signals. Both CCD and flat-panel based detectors use an "active" readout of the image following acquisition to present the image immediately without further interaction by the technologist. Other technologies such as complementary metal-oxide semiconductor (CMOS) detectors were introduced in the same time frame as AMFPI's, but have not as of yet been successful, mainly due to problems with excessive electronic noise.
Beyond the digital detector characteristics are considerations for software for pre- and postprocessing of the digital image data, the user and modality interfaces, display monitors and calibrations. Many unique acquisition capabilities, such as dual-energy image tissue decomposition and limited-angle digital tomosynthesis, are important when considering future applications of specific importance.
The contents and discussion within this article are based on a "generic" description of PSP (CR) and DR detectors. Suffice it to say, there are a wide range and capability of detector systems within each "class" of digital detector technology, and many of the sweeping statements made may or may not be accurate with respect to a specific digital radiography device.
Digital radiography technology
Photostimulable storage phosphor (PSP) detectors
More commonly recognized as CR, the PSP detector "system" is comprised of 2 main components. The detector is usually a cassette-based storage phosphor that absorbs X-ray energy transmitted through the patient...