NEW FIBEROPTIC SCREENS AND FILTRATION FOR X-RAY IMAGING

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This proposal is aimed at improving the diagnostic image quality in radiography and fluoroscopy at a reduced radiation dose. The currently attainable x-ray quantum efficiency of the state-of-the- art rare earth intensifying screens varies from 40-70%. Increase in the quantum efficiency results in unacceptable loss in spatial resolution. Capture of the remaining fraction without resolution loss will lead to improvement in image contrast and reduction in radiation dose. Attempts will be made to attain 100% quantum efficiency by optimization and use of a new type of fluorscent intensifying screen. This new screen is made of scintillating (terbium-doped) optically transparent glass which is also available as a fiberoptic plate. These scintillating fiberoptic plates provide spatial resolution far exceeding that of conventional intensifying screens, with nearly 100% quantum efficiency at diagnostic x-ray energies. In this study we propose to investigate the quantum and conversion efficiency of both plain and fiberoptic scintillating glass, anticipating potential applications in radiologic imaging. The applicability of these materials will be tested for use as intensifying screens in radiology or therapy treatment verification with film, or as input phosphor screens for fluoroscopic image intensifiers. The potential replacement of the present input window and phosphor of conventional intensifiers with a single fiberoptic plate will be explored. For this reason, we also plan to quantify the effect of x-ray scatter from the input window of conventional image intensifiers and find means to reduce it. This will result in an improvement of the contrast of fluoroscopic images, thus increasing the probability of detecting lesions with low subject contrast. The potential degradation in image contrast from the x-ray filters will also be investigated, first by a computational approach and then experimentally. This part of the study will enable us to quantify the scatter fluence from the x-ray filters. We will then be able to identify the filters which produce minimal scattering and improved contrast. The scattering properties and transmission spectra will also be investigated for some important k-edge filters (erbium, gadolinium, lanthanum and samarium). The applicability of these filters will be tested for some radiographic procedures such as mammography and pediatric imaging.