title: Simulation of range imaging-based estimation of respiratory lung motion. Influence of noise, signal dimensionality and sampling patterns.
abstract: OBJECTIVE
  A major problem associated with the irradiation of thoracic and abdominal tumors is respiratory motion. In clinical practice, motion compensation approaches are frequently steered by low-dimensional breathing signals (e.g., spirometry) and patient-specific correspondence models, which are used to estimate the sought internal motion given a signal measurement. Recently, the use of multidimensional signals derived from range images of the moving skin surface has been proposed to better account for complex motion patterns. In this work, a simulation study is carried out to investigate the motion estimation accuracy of such multidimensional signals and the influence of noise, the signal dimensionality, and different sampling patterns (points, lines, regions).
  
  
  METHODS
  A diffeomorphic correspondence modeling framework is employed to relate multidimensional breathing signals derived from simulated range images to internal motion patterns represented by diffeomorphic non-linear transformations. Furthermore, an automatic approach for the selection of optimal signal combinations/patterns within this framework is presented.
  
  
  RESULTS
  This simulation study focuses on lung motion estimation and is based on 28 4D CT data sets. The results show that the use of multidimensional signals instead of one-dimensional signals significantly improves the motion estimation accuracy, which is, however, highly affected by noise. Only small differences exist between different multidimensional sampling patterns (lines and regions). Automatically determined optimal combinations of points and lines do not lead to accuracy improvements compared to results obtained by using all points or lines.
  
  
  CONCLUSIONS
  Our results show the potential of multidimensional breathing signals derived from range images for the model-based estimation of respiratory motion in radiation therapy.
authors.affiliation: Matthias Wilms, Institute of Medical Informatics, University of Lübeck, Ratzeburger Allee 160, 23562 Lübeck, Germany, E-mail: wilms@imi.uni-luebeck.de.
authors.forename: M
authors.initials: M
authors.lastname: Wilms
authors.forename: R
authors.initials: R
authors.lastname: Werner
authors.forename: M
authors.initials: M
authors.lastname: Blendowski
authors.forename: J
authors.initials: J
authors.lastname: Ortmüller
authors.forename: H
authors.initials: H
authors.lastname: Handels
mesh_terms: D016477:Artifacts; D003198:Computer Simulation; D045853:Exhalation / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional / Q000379:methods*; D001239:Inhalation / Q000502:physiology*; D008168:Lung / Q000503:physiopathology* / Q000528:radiation effects; D008175:Lung Neoplasms / Q000532:radiotherapy*; D009068:Movement / Q000502:physiology*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: Respiratory motion; correspondence modeling; image registration; motion estimation; regression