title: Segmentation of radiographic images under topological constraints: application to the femur.
abstract: OBJECTIVE
  A framework for radiographic image segmentation under topological control based on two-dimensional (2D) image analysis was developed. The system is intended for use in common radiological tasks including fracture treatment analysis, osteoarthritis diagnostics and osteotomy management planning.
  
  
  METHODS
  The segmentation framework utilizes a generic three-dimensional (3D) model of the bone of interest to define the anatomical topology. Non-rigid registration is performed between the projected contours of the generic 3D model and extracted edges of the X-ray image to achieve the segmentation. For fractured bones, the segmentation requires an additional step where a region-based active contours curve evolution is performed with a level set Mumford-Shah method to obtain the fracture surface edge. The application of the segmentation framework to analysis of human femur radiographs was evaluated. The proposed system has two major innovations. First, definition of the topological constraints does not require a statistical learning process, so the method is generally applicable to a variety of bony anatomy segmentation problems. Second, the methodology is able to handle both intact and fractured bone segmentation.
  
  
  RESULTS
  Testing on clinical X-ray images yielded an average root mean squared distance (between the automatically segmented femur contour and the manual segmented ground truth) of 1.10 mm with a standard deviation of 0.13 mm. The proposed point correspondence estimation algorithm was benchmarked against three state-of-the-art point matching algorithms, demonstrating successful non-rigid registration for the cases of interest.
  
  
  CONCLUSIONS
  A topologically constrained automatic bone contour segmentation framework was developed and tested, providing robustness to noise, outliers, deformations and occlusions.
authors.affiliation: Department of Mechanical Engineering (Mechatronics), The University of Auckland, Auckland, New Zealand. ppuh001@aucklanduni.ac.nz
authors.forename: Pavan
authors.initials: P
authors.lastname: Gamage
authors.forename: Sheng Quan
authors.initials: SQ
authors.lastname: Xie
authors.forename: Patrice
authors.initials: P
authors.lastname: Delmas
authors.forename: Wei Liang
authors.initials: WL
authors.lastname: Xu
mesh_terms: D000328:Adult; D000465:Algorithms; D003198:Computer Simulation; D005269:Femur / Q000000981:diagnostic imaging*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D008953:Models, Anatomic; D011859:Radiography