title: Extreme leg motion analysis of professional ballet dancers via MRI segmentation of multiple leg postures.
abstract: OBJECTIVE
  Professional ballet dancers are subject to constant extreme motion which is known to be at the origin of many articular disorders. To analyze their extreme motion, we exploit a unique magnetic resonance imaging (MRI) protocol, denoted as 'dual-posture' MRI, which scans the subject in both the normal (supine) and extreme (split) postures. However, due to inhomogeneous tissue intensities and image artifacts in these scans, coupled with unique acquisition protocol (split posture), segmentation of these scans is difficult. We present a novel algorithm that exploits the correlation between scans (bone shape invariance, appearance similarity) in automatically segmenting the dancer MRI images.
  
  
  METHODS
  While validated segmentation algorithms are available for standard supine MRI, these algorithms cannot be applied to the split scan which exhibits a unique posture and strong inter-subject variations. In this study, the supine MRI is segmented with a deformable models method. The appearance and shape of the segmented supine models are then re-used to segment the split MRI of the same subject. Models are first registered to the split image using a novel constrained global optimization, before being refined with the deformable models technique.
  
  
  RESULTS
  Experiments with 10 dual-posture MRI datasets in the segmentation of left and right femur bones reported accurate and robust results (mean distance error: 1.39 ± 0.31 mm).
  
  
  CONCLUSIONS
  The use of segmented models from the supine posture to assist the split posture segmentation was found to be equally accurate and consistent to supine results. Our results suggest that dual-posture MRI can be efficiently and robustly segmented.
authors.affiliation: MIRALab, University of Geneva, Battelle, Building A, 7 rte de Drize, 1227 Carouge, Switzerland. schmid@miralab.ch
authors.forename: Jérôme
authors.initials: J
authors.lastname: Schmid
authors.forename: Jinman
authors.initials: J
authors.lastname: Kim
authors.forename: Nadia
authors.initials: N
authors.lastname: Magnenat-Thalmann
mesh_terms: D000465:Algorithms; D006801:Humans; D007866:Leg / Q000502:physiology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008954:Models, Biological; D009038:Motion; D011187:Posture; D016059:Range of Motion, Articular / Q000502:physiology*
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