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@ARTICLE{Hahn:141899,
      author       = {A. Hahn$^*$ and M. Knaup$^*$ and M. Brehm and S. Sauppe and
                      M. Kachelriess$^*$},
      title        = {{T}wo methods for reducing moving metal artifacts in
                      cone-beam {CT}.},
      journal      = {Medical physics},
      volume       = {45},
      number       = {8},
      issn         = {0094-2405},
      address      = {College Park, Md.},
      publisher    = {AAPM},
      reportid     = {DKFZ-2018-02156},
      pages        = {3671 - 3680},
      year         = {2018},
      abstract     = {In image-guided radiation therapy, fiducial markers or
                      clips are often used to determine the position of the tumor.
                      These markers lead to streak artifacts in cone-beam CT
                      (CBCT) scans. Standard inpainting-based metal artifact
                      reduction (MAR) methods fail to remove these artifacts in
                      cases of large motion. We propose two methods to effectively
                      reduce artifacts caused by moving metal inserts.The first
                      method (MMAR) utilizes a coarse metal segmentation in the
                      image domain and a refined segmentation in the rawdata
                      domain. After an initial reconstruction, metal is segmented
                      and forward projected giving a coarse metal mask in the
                      rawdata domain. Inside the coarse mask, metal is segmented
                      by utilizing a 2D Sobel filter. Metal is removed by linear
                      interpolation in the refined metal mask. The second method
                      (MoCoMAR) utilizes a motion compensation (MoCo) algorithm
                      [Med Phys. 2013;40:101913] that provides us with a
                      motion-free volume (3D) or with a time series of motion-free
                      volumes (4D). We then apply the normalized metal artifact
                      reduction (NMAR) [Med Phys. 2010;37:5482-5493] to these MoCo
                      volumes. Both methods were applied to three CBCT data sets
                      of patients with metal inserts in the thorax or abdomen
                      region and a 4D thorax simulation. The results were compared
                      to volumes corrected by a standard MAR1 [Radiology.
                      1987;164:576-577].MMAR and MoCoMAR were able to remove all
                      artifacts caused by moving metal inserts for the patients
                      and the simulation. Both new methods outperformed the
                      standard MAR1, which was only able to remove artifacts
                      caused by metal inserts with little or no motion.In this
                      work, two new methods to remove artifacts caused by moving
                      metal inserts are introduced. Both methods showed good
                      results for a simulation and three patients. While the first
                      method (MMAR) works without any prior knowledge, the second
                      method (MoCoMAR) requires a respiratory signal for the MoCo
                      step and is computationally more demanding and gives no
                      benefit over MMAR, unless MoCo images are desired.},
      cin          = {E020 / E025},
      ddc          = {610},
      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:29938797},
      doi          = {10.1002/mp.13060},
      url          = {https://inrepo02.dkfz.de/record/141899},
}