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@ARTICLE{Sawall:125395,
      author       = {S. Sawall$^*$ and J. Maier$^*$ and C. Leinweber$^*$ and C.
                      Funck$^*$ and J. Kuntz$^*$ and M. Kachelriess$^*$},
      title        = {{M}odel-based sphere localization ({MBSL}) in x-ray
                      projections.},
      journal      = {Physics in medicine and biology},
      volume       = {62},
      number       = {16},
      issn         = {1361-6560},
      address      = {Bristol},
      publisher    = {IOP Publ.},
      reportid     = {DKFZ-2017-01525},
      pages        = {6486 - 6496},
      year         = {2017},
      abstract     = {The detection of spherical markers in x-ray projections is
                      an important task in a variety of applications, e.g.
                      geometric calibration and detector distortion correction.
                      Therein, the projection of the sphere center on the detector
                      is of particular interest as the used spherical beads are no
                      ideal point-like objects. Only few methods have been
                      proposed to estimate this respective position on the
                      detector with sufficient accuracy and surrogate positions,
                      e.g. the center of gravity, are used, impairing the results
                      of subsequent algorithms. We propose to estimate the
                      projection of the sphere center on the detector using a
                      simulation-based method matching an artificial projection to
                      the actual measurement. The proposed algorithm intrinsically
                      corrects for all polychromatic effects included in the
                      measurement and absent in the simulation by a polynomial
                      which is estimated simultaneously. Furthermore, neither the
                      acquisition geometry nor any object properties besides the
                      fact that the object is of spherical shape need to be known
                      to find the center of the bead. It is shown by simulations
                      that the algorithm estimates the center projection with an
                      error of less than [Formula: see text] of the detector pixel
                      size in case of realistic noise levels and that the method
                      is robust to the sphere material, sphere size, and
                      acquisition parameters. A comparison to three reference
                      methods using simulations and measurements indicates that
                      the proposed method is an order of magnitude more accurate
                      compared to these algorithms. The proposed method is an
                      accurate algorithm to estimate the center of spherical
                      markers in CT projections in the presence of polychromatic
                      effects and noise.},
      cin          = {E020 / E025},
      ddc          = {570},
      cid          = {I:(DE-He78)E020-20160331 / I:(DE-He78)E025-20160331},
      pnm          = {315 - Imaging and radiooncology (POF3-315)},
      pid          = {G:(DE-HGF)POF3-315},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:28632499},
      doi          = {10.1088/1361-6560/aa7a96},
      url          = {https://inrepo02.dkfz.de/record/125395},
}