Theoretical investigation of detector MTF of polycrystalline mercuric iodide x-ray converters incorporating Frisch grid structures for digital breast tomosynthesis

Liuxing Shen; Youcef El-Mohri; Albert K. Liang; Qihua Zhao; Larry E. Antonuk; Ian A. Cunningham

doi:10.1117/12.2581092

15 February 2021 Theoretical investigation of detector MTF of polycrystalline mercuric iodide x-ray converters incorporating Frisch grid structures for digital breast tomosynthesis

Liuxing Shen, Youcef El-Mohri, Albert K. Liang, Qihua Zhao, Larry E. Antonuk, Ian A. Cunningham

Author Affiliations +

Proceedings Volume 11595, Medical Imaging 2021: Physics of Medical Imaging; 1159517 (2021) https://doi.org/10.1117/12.2581092
Event: SPIE Medical Imaging, 2021, Online Only

Abstract

The DQE performance of active matrix flat-panel imagers (AMFPIs) degrades under low dose conditions – such as those encountered in digital breast tomosynthesis where electronic additive noise becomes comparable to imaging signal. Compared to commercially available x-ray converter materials such as CsI:Tl and a-Se, particle-in-binder polycrystalline mercuric iodide (PIB HgI₂) offers imaging signal 3 to 10 times larger. However, PIB HgI₂ exhibits an unacceptably high degree of image lag, believed to originate from the trapping of holes. To suppress hole signal contribution (with the expectation of decreasing image lag), a Frisch grid structure embedded within a PIB HgI₂ detector is under investigation. In this theoretical study involving finite element analysis modeling, the effects of grid design and charge carrier lifetimes on the line spread function and modulation transfer function (MTF) were investigated. Two design parameters were considered: grid pitch (defined as the center-to-center distance between adjacent grid elements) and R_GRID (defined as the ratio of grid element width to grid pitch). Results show that for a grid pitch comparable to the pixel pitch (i.e., 100 μm) and high R_GRID, MTF is significantly degraded compared to a detector without a grid while, for a grid pitch of 20 μm, MTF is largely maintained and is almost independent of R_GRID. The best identified design is a grid pitch of 20 μm and R_GRID of 45% – providing an MTF similar to that of a detector without a grid while suppressing hole signal by 78%. This work is supported by NIH grant R01-EB022028.

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Liuxing Shen, Youcef El-Mohri, Albert K. Liang, Qihua Zhao, Larry E. Antonuk, and Ian A. Cunningham "Theoretical investigation of detector MTF of polycrystalline mercuric iodide x-ray converters incorporating Frisch grid structures for digital breast tomosynthesis", Proc. SPIE 11595, Medical Imaging 2021: Physics of Medical Imaging, 1159517 (15 February 2021); https://doi.org/10.1117/12.2581092

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