Principles of digital radiography with large-area, electronically readable detectors: a review of the basics.

The practice of digital radiographic imaging is poised to undergo dramatic change in the very near future owing to a rapid proliferation of electronically readable x-ray detectors. Although self-scanning, direct-readout digital detectors have been in use since the introduction of the charged-coupled device (CCD) almost 30 years ago, recent advances in manufacturing technology have made possible a new generation of large-area, flat-panel detectors with integrated, thin-film transistor readout mechanisms. The excitement surrounding this new technology is based on two factors—the promise of very rapid access to digital images wherever radiography with stationary x-ray equipment is performed and the anticipation of image quality that exceeds that of both screen-film receptors and photostimulable storage phosphor computed radiographic systems because of improvements in x-ray detector technology. As digital radiography continues this rapid evolution, it is likely that radiologists will be inundated with information concerning a wide variety of large-area, flat-panel electronic detectors. Unfortunately, it is also likely that there will be a tendency to think of these devices as equivalent, interchangeable commodities because they will be similar in physical size, appearance, and targeted applications. It must be emphasized, however, that important differences exist among these detectors, and differences in digital image quality among the various systems are inevitable and may be quite large. To minimize confusion, therefore, it is important that radiologists have a working understanding of this emerging technology. In this report, we provide an overview of digital electronic x-ray detectors, including two broad classes of detectors based on thin-film transistor arrays and the older, CCD-based designs. Computed radiographic systems based on photostimulable storage phosphors are omitted from this report because they do not contain integrated readout mechanisms (1). Our goal is to provide a brief review of the basic methods, designs, and materials used in direct-readout radiographic systems and to emphasize important characteristics that may affect system performance and image quality. The advantages and disadvantages of the different detectors, as well as the important factors that should be considered when performing a critical analysis of these new digital imaging systems, are discussed.