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@ARTICLE{Elter:166497,
      author       = {A. Elter$^*$ and E. Hellwich$^*$ and S. Dorsch$^*$ and M.
                      Schäfer$^*$ and A. Runz$^*$ and S. Klüter and B. Ackermann
                      and S. Brons and C. P. Karger$^*$ and P. Mann$^*$},
      title        = {{D}evelopment of phantom materials with independently
                      adjustable {CT}- and {MR}-contrast at 0.35, 1.5 and 3{T}.},
      journal      = {Physics in medicine and biology},
      volume       = {66},
      number       = {4},
      issn         = {1361-6560},
      address      = {Bristol},
      publisher    = {IOP Publ.},
      reportid     = {DKFZ-2020-02940},
      pages        = {045013},
      year         = {2021},
      note         = {#EA:E040#LA:E040# / 2021 Feb 3;66(4):045013},
      abstract     = {Quality assurance in magnetic resonance (MR)-guided
                      radiotherapy (RT) lacks anthropomorphic phantoms that
                      represent tissue-equivalent imaging contrast in both
                      computed tomography (CT) and MR imaging. In this study, we
                      developed phantom materials with individually adjustable CT
                      value as well as T1- and T2-relaxation times in MR imaging
                      at three different magnetic field strengths. Additionally,
                      their experimental stopping power ratio (SPR) for carbon
                      ions was compared with predictions based on single- and
                      dual-energy CT. Ni-DTPA doped agarose gels were used for
                      individual adjustment of T1and T2at 0.35,1.5 and 3.0 T. The
                      CT value was varied by adding potassium chloride (KCl). By
                      multiple linear regression, equations for the determination
                      of agarose, Ni-DTPA and KCl concentrations for given T1,
                      T2and CT values were derived and employed to produce nine
                      specific soft tissue samples. Experimental T1, T2and CT
                      values of these soft tissue samples were compared with
                      predictions and additionally, carbon ion SPR obtained by
                      range measurements were compared with predictions based on
                      single- and dual-energy CT. The measured CT value, T1and
                      T2of the produced soft tissue samples agreed very well with
                      predictions based on the derived equations with mean
                      deviations of less than 3.5 $\%.$ While single-energy CT
                      overestimates the measured SPR of the soft tissue samples,
                      the dual-energy CT-based predictions showed a mean SPR
                      deviation of only (0.2±0.3) $\%.$ To conclude,
                      anthropomorphic phantom materials with independently
                      adjustable CT values as well as T1and T2relaxation times at
                      three different magnetic field strengths were developed. The
                      derived equations describe the material specific relaxation
                      times and the CT value in dependence on agarose, Ni-DTPA and
                      KCl concentrations as well as the chemical composition of
                      the materials based on given T1,T2and CT value. Dual-energy
                      CT allows accurate prediction of the carbon ion range in
                      these materials.},
      keywords     = {MR-guided radiotherapy (MRgRT) (Other) / end-to-end tests
                      (Other) / magnetic resonance imaging (MRI) and computed
                      tomography (CT) contrast (Other) / phantom materials (Other)
                      / quality assurance (Other)},
      cin          = {E040 / E010},
      ddc          = {530},
      cid          = {I:(DE-He78)E040-20160331 / I:(DE-He78)E010-20160331},
      pnm          = {315 - Bildgebung und Radioonkologie (POF4-315)},
      pid          = {G:(DE-HGF)POF4-315},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:33333496},
      doi          = {10.1088/1361-6560/abd4b9},
      url          = {https://inrepo02.dkfz.de/record/166497},
}