PubMed · 5675700
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
J F Reus, W P Pare. 1968. A DC-coupled photocell trigger.. https://doi.org/10.2466/pms.1968.26.3c.1265
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Noise properties of active matrix, flat-panel imagers under conditions relevant to diagnostic radiology are investigated. These studies focus on imagers based upon arrays with pixels incorporating a discrete photodiode coupled to a thin-film transistor, both fabricated from hydrogenated amorphous silicon. These optically sensitive arrays are operated with an overlying x-ray converter to allow indirect detection of incident x rays. External electronics, including gate driver circuits and preamplification circuits, are also required to operate the arrays. A theoretical model describing the signal and noise transfer properties of the imagers under conditions relevant to diagnostic radiography, fluoroscopy, and mammography is developed. This frequency-dependent model is based upon a cascaded systems analysis wherein the imager is conceptually divided into a series of stages having intrinsic gain and spreading properties. Predictions from the model are compared with x-ray sensitivity and noise measurements obtained from individual pixels from an imager with a pixel format of 1536 x 1920 pixels at a pixel pitch of 127 microns. The model is shown to be in excellent agreement with measurements obtained with diagnostic x rays using various phosphor screens. The model is used to explore the potential performance of existing and hypothetical imagers for application in radiography, fluoroscopy, and mammography as a function of exposure, additive noise, and fill factor. These theoretical predictions suggest that imagers of this general design incorporating a CsI: Tl intensifying screen can be optimized to provide detective quantum efficiency (DQE) superior to existing screen-film and storage phosphor systems for general radiography and mammography. For fluoroscopy, the model predicts that with further optimization of a-Si:H imagers, DQE performance approaching that of the best x-ray image intensifier systems may be possible. The results of this analysis suggest strategies for future improvements of this imaging technology.
The calculation of lens coupling efficiency is often performed in the design of lens coupled digital radiographic system, now currently under development. With these systems, an electronic camera is focused onto a planar scintillator such as a conventional intensifying screen. Historically, this calculation has relied on certain assumptions concerning the emission properties of the scintillator, and primarily this assumption is that the scintillator is either a Lambertain emitter (light is emitted over all angles equally) or a point radiator. Because there now exists new classes of scintillators such as scintillating fiber optic screens and pixelated intensifying screens, it is sometimes necessary to perform lens coupling calculations in the absence of the Lambertian and point source assumptions. In this paper we describe the necessary equations to accurately calculate lens coupling efficiency in the most general of cases. Graphical examples demonstrate the lens coupling efficiency for hypothetical Lambertain scintillating sources, for a rare earth intensifying screen, and for a scintillating fiber optical screen.
Clinical efficacy of diagnostic radiology for mammographic examinations is critically dependent on source characteristics, detection efficiency, image resolution and applied high voltage. In this report we focus on means for evaluation of source-dependent issues including noninvasive determination of the applied high voltage, and characterization of intrinsic spectral distributions which in turn reflect the effects of added filtration and target and window contamination. It is shown that a particular form of x-ray curved crystal spectrometry with electronic imaging can serve to determine all relevant parameters within the confines of a standard clinical exposure.