title: Anisotropic imaging performance in indirect x-ray imaging detectors.
abstract: We report on the variability in imaging system performance due to oblique x-ray incidence, and the associated transport of quanta (both x rays and optical photons) through the phosphor, in columnar indirect digital detectors. The analysis uses MANTIS, a combined x-ray, electron, and optical Monte Carlo transport code freely available. We describe the main features of the simulation method and provide some validation of the phosphor screen models considered in this work. We report x-ray and electron three-dimensional energy deposition distributions and point-response functions (PRFs), including optical spread in columnar phosphor screens of thickness 100 and 500 microm, for 19, 39, 59, and 79 keV monoenergetic x-ray beams incident at 0 degrees, 10 degrees, and 15 degrees. In addition, we present pulse-height spectra for the same phosphor thickness, x-ray energies, and angles of incidence. Our results suggest that the PRF due to the phosphor blur is highly nonsymmetrical, and that the resolution properties of a columnar screen in a tomographic, or tomosynthetic imaging system varies significantly with the angle of x-ray incidence. Moreover, we find that the noise due to the variability in the number of light photons detected per primary x-ray interaction, summarized in the information or Swank factor, is somewhat independent of thickness and incidence angle of the x-ray beam. Our results also suggest that the anisotropy in the PRF is not less in screens with absorptive backings, while the noise introduced by variations in the gain and optical transport is larger. Predictions from MANTIS, after additional validation, can provide the needed understanding of the extent of such variations, and eventually, lead to the incorporation of the changes in imaging performance with incidence angle into the reconstruction algorithms for volumetric x-ray imaging systems.
authors.affiliation: Division of Imaging and Applied Mathematics, Office of Science and Engineering Labs, Center for Devices and Radiological Health, U.S. Food & Drug Administration, 12720 Twinbrook Parkway, Rockville, Maryland 20857, USA. aldo.badano@fda.hhs.gov
authors.forename: Aldo
authors.initials: A
authors.lastname: Badano
authors.forename: Iacovos S
authors.initials: IS
authors.lastname: Kyprianou
authors.forename: Josep
authors.initials: J
authors.lastname: Sempau
mesh_terms: D016880:Anisotropy; D003198:Computer Simulation; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D015233:Models, Statistical; D009010:Monte Carlo Method; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement / Q000295:instrumentation* / Q000379:methods; D011874:Radiometry / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014159:Transducers