2 May 1997 Performance of a CsI:TL-screen-based scanning slot detector for digital mammography
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Abstract
Thallium activated CsI scintillation screen (CsI:Tl) has advantages over rare-earth phosphor screens when used in a scanning slot x-ray detector for digital mammography. The scintillation decay time for CsI:Tl is only approximately 1 microsecond(s) which eliminates the afterglow effect associated with the use of rare-earth phosphor. The CsI needles serve to limit the spread of the scintillation light which permits the use of a relatively thick CsI:Tl screen to improve detector x-ray interaction efficiency without sacrificing resolution performance. A prototype scanning slot detector was made of a CsI:Tl screen and was optically coupled to two CCDs by plastic optical fiber image guides. The screen was composed of prismatic CsI crystals with a needle size of approximately 5 micrometers . Image guides used in the detector had an input to output ratio of 1:1, and were made of 10 micrometers diameter plastic optical fibers. Each CCD, operated in the time-delayed integration mode, was an 1100 X 330 pixel array with pixel size of 24 micrometers . A full scale scanning slot detector will contain eight rather than two such modules. The x-ray interaction efficiency of the slot x-ray detector was calculated to be approximately 84 percent at 20 keV for the CsI:Tl screen, and was approximately 20 percent greater than that of a 31.7 mg/cm2 thick Gd2O2S:Tb phosphor screen. Limiting spatial resolution was investigated by taking the images of a 1 degree star resolution test pattern as a function of detector scan speed. Limiting spatial resolution was approximately 15 1p/mm at a scan speed of 4 cm/s and improved only slightly to approximately 16 1p/mm as the scanning speed decreased to 1 cm/s.
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Zhenxue Jing, Walter Huda, James K. Walker, Won Y. Choi, "Performance of a CsI:TL-screen-based scanning slot detector for digital mammography", Proc. SPIE 3032, Medical Imaging 1997: Physics of Medical Imaging, (2 May 1997); doi: 10.1117/12.273994; https://doi.org/10.1117/12.273994
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