DIGITAL RADIOGRAPHY : CURRENT STATUS AND FUTURE POTENTIALS

Abstract

The motivation for development of digital radiography (DR) systems are related to cost reduction in diagnostic examinations, improvement in diagnostic accuracy and utility, reduction in patient exposure, flexibility of image display and processing, efficient image data storage and retrieval, and overall convenience. Major components of DR systems include x-ray detection, digitization, image processing and image display. Prototype units currently available are AS&E Medical Miro-Dose X-ray System, Picker Digital Chest System, various DSA units using image intensifier-TV system, ADAC Projection Digital X-ray System, Fuji Computed Radiography, and film-based DR system. Important physical properties of DR systems are sensitivity (or relative patient exposure), resolution, noise, system response (or dynamic range), scatter rejection and contrast sensitivity. Factors affecting resolution properties of DR systems involve X-ray beam characteristics, detector response, sampling aperture (or pixel size), sampling rate, display aperture and image processing. Factors affecting their noise are quatum noise, sampling aperture, sampling rate, quantization level, image processing and inherent system noise. Image processing techniques employed include windowing, zooming, filtering (smoothing, highpass filtering, unsharp masking, etc.), averaging, temporal subtraction, recursive filtering, matched filtering, energy subtraction, and hybrid subtraction. Effects of these image processing techniques are to eliminate structured noise, to increase dynamic range and/or to improve detection and visibility of radiologic objects. Digital radiography is a promising new approach for x-ray imaging system in diagnostic radiology. However, DR is, in many respects, much more complicated than conventional analog approach. Prior to the replacement of conventional techniques, it will be necessary to fully understand the impact of this new approach to all phases of diagnostic radiology.