This application proposes an ambitious program of research to develop a new, real-time, digital, flat-panel imaging technology based upon a Multi- element Amorphous Silicon Detector Array for X-ray imaging (MASDA-X). The radiation-resistant array will consist of a 2-dimensional, self-scanning matrix of 2500 x 2500 pixels at a pixel pitch of 100 microns giving a 25 x 25 cm square imaging area. The imager consists of an x-ray converter, the array, and the associated acquisition electronics. Such imagers offer significant potential advantages over existing technologies including: (a) digital radiographic imaging with immediate image capture and presentation at equivalent or perhaps even considerably less exposure than film-screen and CR systems: (b) real-time fluoroscopic imaging with a compact unit the size of a film-cassette and with image quality free of the effects of distortion and glare that affect x-ray image intensifier (XRII) systems; (c) exposure and dynamic range comparable to that of CR systems and large compared to film-screen systems; (d) a spatial resolution of 5 l p/mm which is superior to that of existing XRII units; and (e) low cost devices offering low-maintenance and assured quality imaging. The overall objective of this research is to determine if flat-panel technology is capable of creating imaging devices with performance comparable or superior to established technologies (eg. film-screen and CR for radiography and XRII systems for fluoroscopy). The specific aims of the research are: (l) development of the imaging system in a manner so as to optimize imaging performance separately for radiography and fluoroscopy. The optimization method will involve an iterative procedure of imager construction, performance evaluation, theoretical modeling, and design improvement; (2) creation of the acquisition electronics necessary to allow optimal signal-to-noise performance of the imager and execution of the imager studies; (3) thorough quantification of the performance of the imager through measurement of its properties including observer- independent performance variables: MTF(f), DQE(f), and NPS(f) to determine how the signal and noise properties of this imager compare to those of existing technologies; (4) execution of initial quantitative examination of the possible clinical utility of the imager through observer-dependent studies comparing the performance of the flat-panel imager to that of state-of-the-art film-screen, CR, and XRII systems employing a variety of phantoms. If the performance of flat-panel x-ray imagers can be made acceptable, their potential advantages are such that this technology could become a major radiological tool early in the 21st century with a correspondingly profound impact upon health care. The proposed research will answer the essential questions of whether imagers built from this technology offer quantitative performance comparable or superior to current established technologies and thus warrant the massive investments that will be required to bring such matters into clinical use.