Physics of Medical Imaging

Geometric calibration and correction for a lens-coupled detector in x-ray phase-contrast imaging

[+] Author Affiliations
Alex George, Peter Y. Chen, Alejandro Morales-Martinez, Alireza Panna, Andrew A. Gomella, Eric E. Bennett, Han Wen

National Institutes of Health, National Heart, Lung and Blood Institute, Biochemistry and Biophysics Center, Imaging Physics Laboratory, Bethesda, Maryland, United States

J. Med. Imag. 4(1), 013507 (Mar 24, 2017). doi:10.1117/1.JMI.4.1.013507
History: Received August 23, 2016; Accepted March 2, 2017
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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.

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© 2017 Society of Photo-Optical Instrumentation Engineers

Citation

Alex George ; Peter Y. Chen ; Alejandro Morales-Martinez ; Alireza Panna ; Andrew A. Gomella, et al.
"Geometric calibration and correction for a lens-coupled detector in x-ray phase-contrast imaging", J. Med. Imag. 4(1), 013507 (Mar 24, 2017). ; http://dx.doi.org/10.1117/1.JMI.4.1.013507


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