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Proceedings Paper

Digital indirect-detection x-ray imagers with microlens focusing: effects of Fresnel reflections from the microlens layer
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Paper Abstract

We have been investigating whether a microlens layer placed between the phosphor and the photodetector can improve indirect detection x-ray imagers. Using a simulation study, we analyzed the light collection properties of the proposed imager taking into account Fresnel reflection and transmission properties of the lenses and the screen. A digital x-ray imager combining an 82-μm-thick Gd2O2S:Tb phosphor screen, a fused silica microlens layer, and a 127-μm pixel pitch photodetector (optical fill factor of 57%) were modeled. The light collection for the prototypes varied from 53% to 69% for lens thicknesses ranging from 10 to 50 μm. The full-width half-maximum (FWHM) of the light spread function ranged from 177-192 μm. 4-8% of the light was reflected back into the phosphor screen when correctly taking into account Fresnel reflections for these prototype imagers. In comparison, 56% of the light was collected and the FWHM of the light spread function was 174 μm for a conventional imager with the screen in direct contact with the photodetector. We observed that the light collection was overestimated by 6-9% but the spread functions were basically unaffected when the Fresnel assumption was not utilized in the simulations. This study shows that a properly designed microlens layer can more than offset Fresnel losses, thereby producing an improved digital x-ray imager.

Paper Details

Date Published: 5 June 2003
PDF: 7 pages
Proc. SPIE 5030, Medical Imaging 2003: Physics of Medical Imaging, (5 June 2003); doi: 10.1117/12.479995
Show Author Affiliations
Nicholas Petrick, CDRH/U.S. Food and Drug Administration (United States)
Univ. of Michigan (United States)
Aldo Badano, CDRH/U.S. Food and Drug Administration (United States)
Heang-Ping Chan, Univ. of Michigan (United States)
Berkman Sahiner, Univ. of Michigan (United States)
Lubomir M. Hadjiiski, Univ. of Michigan (United States)

Published in SPIE Proceedings Vol. 5030:
Medical Imaging 2003: Physics of Medical Imaging
Martin J. Yaffe; Larry E. Antonuk, Editor(s)

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