Impact of computers in radiography: The advent of digital radiography, Part-2

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In the first part of this article, fundamental concepts regarding analog and digital signals, basic principal of radiography and simplified definitions of some frequently used terms in digital radiography were dwelt upon. Digital radiography systems were defined and categorized into Computed Radiography (CR) and Direct Digital radiography (DR) systems followed by a brief description of the CR systems.[1] Advantages and limitations of film screen radiography (FSR), digital radiography systems in general and CR systems in particular were also listed in a tabular form. To recap, computed radiography (CR) systems use a photostimulable phosphor plate enclosed in a cassette. In CR, image acquisition is a two-stage process wherein image capture and image read out are done separately. Direct digital radiography (DR) systems, on the other hand, use detectors that have a combined image capture and image read out capability. DR systems are also called as DDR or ddR systems by some vendors. This second part of this article focuses on DR systems Direct digital radiographic systems Cassettes form an important component in both film-screen radiography (FSR) and CR.[2] To improve workflow and to avoid the use of cassettes, a new class of detectors was manufactured that combined the processes of image capture and image read-out. This formed the evolutionary basis of DR systems. A functional overview of DR systems is given in Table 1. Table 1 Advantages and limitations of direct digital radiography