title: Image-based iterative compensation of motion artifacts in computed tomography.
abstract: OBJECTIVE
  This article presents an iterative method for compensation of motion artifacts for slowly rotating computed tomography (CT) systems. Patient's motion introduces inconsistencies among projections and yields severe reconstruction artifacts for free-breathing acquisitions. Streaks and doubling of structures can appear and the resolution is limited by strong blurring.
  
  
  METHODS
  The rationale of the proposed motion compensation method is to iteratively correct the reconstructed image by first decomposing the perceived motion in projection space, then reconstructing the motion artifacts in image space, and finally subtracting the artifacts from an initial image. The initial image is reconstructed from the acquired data and might contain motion blur artifacts but, nevertheless, is considered as a reference for estimating the reconstruction artifacts.
  
  
  RESULTS
  Qualitative and quantitative figures are shown for experiments based on numerically simulated projections of a sequence of clinical images resulting from a respiratory-gated helical CT acquisition. The border of the diaphragm becomes progressively sharper and the contrast improves for small structures in the lungs.
  
  
  CONCLUSIONS
  The originality of the technique stems from the fact that the patient motion is not explicitly estimated but the motion artifacts are reconstructed in image space. This approach could provide sharp static anatomical images on interventional C-arm systems or on slowly rotating X-ray equipments in radiotherapy.
authors.affiliation: Philips Research Europe, Weisshausstrasse 2, 52066 Aachen, Germany. colas.schretter@philips.com
authors.forename: Colas
authors.initials: C
authors.lastname: Schretter
authors.forename: Georg
authors.initials: G
authors.lastname: Rose
authors.forename: Matthias
authors.initials: M
authors.lastname: Bertram
mesh_terms: D000465:Algorithms; D016477:Artifacts; D003198:Computer Simulation; D003964:Diaphragm / Q000000981:diagnostic imaging; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D009038:Motion; D019047:Phantoms, Imaging; D013902:Radiography, Thoracic / Q000379:methods; D012119:Respiration; D012399:Rotation; D014057:Tomography, X-Ray Computed / Q000379:methods*