title: Geometric calibration and correction for a lens-coupled detector in x-ray phase-contrast imaging.
abstract: A lens-coupled x-ray camera with a tilted phosphor collects light emission from the x-ray illuminated (front) side of phosphor. Experimentally, it has been shown to double x-ray photon capture efficiency and triple the spatial resolution along the phosphor tilt direction relative to the same detector at normal phosphor incidence. These characteristics benefit grating-based phase-contrast methods, where linear interference fringes need to be clearly resolved. However, both the shallow incident angle on the phosphor and lens aberrations of the camera cause geometric distortions. When tiling multiple images of limited vertical view into a full-field image, geometric distortion causes blurring due to image misregistration. Here, we report a procedure of geometric correction based on global polynomial transformation of image coordinates. The corrected image is equivalent to one obtained with a single full-field flat panel detector placed at the sample plane. In a separate evaluation scan, the position deviations in the horizontal and vertical directions were reduced from 0.76 and 0.028 mm, respectively, to 0.006 and 0.009 mm, respectively, by the correction procedure, which were below the 0.028-mm pixel size of the imaging system. In a demonstration of a phase-contrast imaging experiment, the correction reduced blurring of small structures.
authors.affiliation: National Institutes of Health , National Heart, Lung and Blood Institute, Biochemistry and Biophysics Center, Imaging Physics Laboratory, Bethesda, Maryland, United States.
authors.forename: Alex
authors.initials: A
authors.lastname: George
authors.affiliation: National Institutes of Health , National Heart, Lung and Blood Institute, Biochemistry and Biophysics Center, Imaging Physics Laboratory, Bethesda, Maryland, United States.
authors.forename: Peter Y
authors.initials: PY
authors.lastname: Chen
authors.affiliation: National Institutes of Health , National Heart, Lung and Blood Institute, Biochemistry and Biophysics Center, Imaging Physics Laboratory, Bethesda, Maryland, United States.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Morales-Martinez
authors.affiliation: National Institutes of Health , National Heart, Lung and Blood Institute, Biochemistry and Biophysics Center, Imaging Physics Laboratory, Bethesda, Maryland, United States.
authors.forename: Alireza
authors.initials: A
authors.lastname: Panna
authors.affiliation: National Institutes of Health , National Heart, Lung and Blood Institute, Biochemistry and Biophysics Center, Imaging Physics Laboratory, Bethesda, Maryland, United States.
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Gomella
authors.affiliation: National Institutes of Health , National Heart, Lung and Blood Institute, Biochemistry and Biophysics Center, Imaging Physics Laboratory, Bethesda, Maryland, United States.
authors.forename: Eric E
authors.initials: EE
authors.lastname: Bennett
authors.affiliation: National Institutes of Health , National Heart, Lung and Blood Institute, Biochemistry and Biophysics Center, Imaging Physics Laboratory, Bethesda, Maryland, United States.
authors.forename: Han
authors.initials: H
authors.lastname: Wen
keywords: geometric correction; image distortion; phase contrast; tilted phosphor; x-ray