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Optimized Detector Configuration for Polarized X-Ray Fluorescence Computed Tomography

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D Vernekohl

D Vernekohl*, L Xing , Stanford Univ School of Medicine, Stanford, CA


SU-K-702-11 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 702

Purpose: The use of polarized x-ray radiation is common in synchrotron based x-ray fluorescence computed tomography (XFCT). However, the impact of scatter reduction for different target and source geometries was never quantified. The purpose of this study is to quantify these dependencies and to derive an optimized detector geometry for the imaging of gold nanoparticles with polarized x-rays.

Methods: The effect of polarization on scatter background is modeled with Monte-Carlo simulations where a full XFCT scan is performed by translating and rotating a pencil beam around a mouse sized phantom. The detector is a half sphere oriented backwards to the pencil beam to minimize the Compton scatter. The quantitative scatter reduction between polarized and unpolarized radiation is compared for small spectral detectors at different detection angles. To analyze the advantage for large area detectors, the scatter reduction is analyzed for elliptical and circular cuts from the half sphere detector. Optimized ellipse geometries are determined empirically with an automatized data analysis and verified in image domain.

Results: For the spectral detector analysis, the scatter is maximally reduced by a factor of 5.5 at a scatter angle of 90° and the lowest scatter reduction quantified as 1.36 for an angle of 172°.The performance for large area detectors shows that elliptical geometries provide better scatter reduction when optimized. For fixed circular radii of 100, 139, and 192 mm, the scatter can be reduced by 27.1, 33.5, and 73.4%, respectively. The detection threshold improved by 15.7, 22.7, and 53.7% respectively.

Conclusion: The study shows that the scatter reduction is substantial when small spectroscopic detectors are positioned perpendicular to the polarization direction; resulting in 1.36-5.5 fold scatter suppression. In regard of detectors with large angle coverage, the polarization effect allows to employ advanced detector geometries to minimize scatter events.

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