title: Combined surface and volume processing for fused joint segmentation.
abstract: OBJECTIVE
  Segmentation of rheumatoid joints from CT images is a complicated task. The pathological state of the joint results in a non-uniform density of the bone tissue, with holes and irregularities complicating the segmentation process. For the specific case of the shoulder joint, existing segmentation techniques often fail and lead to poor results. This paper describes a novel method for the segmentation of these joints.
  
  
  METHODS
  Given a rough surface model of the shoulder, a loop that encircles the joint is extracted by calculating the minimum curvature of the surface model. The intersection points of this loop with the separate CT-slices are connected by means of a path search algorithm. Inaccurate sections are corrected by iteratively applying a Hough transform to the segmentation result.
  
  
  RESULTS
  As a qualitative measure we calculated the Dice coefficient and Hausdorff distances of the automatic segmentations and expert manual segmentations of CT-scans of ten severely deteriorated shoulder joints. For the humerus and scapula the median Dice coefficient was 98.9% with an interquartile range (IQR) of 95.8-99.4 and 98.5% (IQR 98.3-99.2%), respectively. The median Hausdorff distances were 3.06 mm (IQR 2.30-4.14) and 3.92 mm (IQR 1.96 -5.92 mm), respectively.
  
  
  CONCLUSIONS
  The routine satisfies the criterion of our particular application to accurately segment the shoulder joint in under 2 min. We conclude that combining surface curvature, limited user interaction and iterative refinement via a Hough transform forms a satisfactory approach for the segmentation of severely damaged arthritic shoulder joints.
authors.affiliation: Department of Orthopaedics, Leiden University Medical Center, Leiden, The Netherlands. p.r.krekel@lumc.nl
authors.forename: Peter R
authors.initials: PR
authors.lastname: Krekel
authors.forename: Edward R
authors.initials: ER
authors.lastname: Valstar
authors.forename: Frits H
authors.initials: FH
authors.lastname: Post
authors.forename: P M
authors.initials: PM
authors.lastname: Rozing
authors.forename: Charl P
authors.initials: CP
authors.lastname: Botha
mesh_terms: D001172:Arthritis, Rheumatoid / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional / Q000379:methods*; D010363:Pattern Recognition, Automated; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D012785:Shoulder Joint / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods*