The imaging performance of a storage phosphor system (SPS) for digital projection radiography is studied in which the x-ray image is temporarily stored in a light-stimulable phosphor plate which is subsequently read out by a scanning laser beam. The imaging performance of this system has been analyzed for two types of imaging plates. The spatial resolution is described by the modulation transfer function and the signal-to-noise (S/N) ratios of the recorded image data are measured in terms of noise-equivalent quanta and detective quantum efficiency. Their dependence on detector entrance dose and spatial frequency is discussed. A detailed analysis of the different sources of image noise is given to outline the intrinsic features and limits of the system. Finally, the S/N behavior of the SPS is compared with published data of screen-film systems.

This contribution discusses a selection of today's techniques and futurc concepts for digital x-ray imaging in medicine. Advantages of digital imaging over conventional analog methods include the possibility to archive and transmit images in digital intormation systems as well as to digitally process pictures before display, for example, to enhance low contrast details. After reviewing two digital x-ray radiography systems for the capture of süll x-ray images, we examine the real time acquisition of dynamic x-ray images (x-ray fluoroscopy). Here, particular attention is paid to the implications of introducing charge-coupled device cameras. We then present a new unified radiography/fluoroscopy solid-state detector concept. As digital image quality is predominantly determined by the relation of signal and noise, aspects of signal transfer, noise, and noise-related quality measures like detective quantum efficiency feature prominently in our discussions. Finally, we descibe a digital image processing algorithm for the reduction of noise in images acquired with low x-ray dose. @ 19ss SptE and tS&T. [s1 01 7-e909(99)00401-8]

The dream ofan all-solid state large area x-ray image sensor with digital readout and full dynamic performance will most probably find a first realisation in two-dimensional thin-film amorphous silicon arrays. In this paper we address in particular the evaluation of the limits of the signal/noise ratio in this concept. Using small prototype detectors measurements of MTF and noise power spectra have been made as a function of x-ray dose. The results are given in terms of the detective quantum efficiency (DQE) as a function of dose and spatial frequency. We further present an analysis of the different noise so rces and their dependence on the detector parameters, and we provide estimates on the maximum signals that may be achieved per unit dose. The intrinsic lag of the amorphous silicon photodiodes causes a second problem area with this type ofx-ray detectors. Especially in radiography/fluoroscopy mixed applications, memory effects may not be negligible.

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