title: Model-based segmentation in orbital volume measurement with cone beam computed tomography and evaluation against current concepts.
abstract: OBJECTIVE
  Objective determination of the orbital volume is important in the diagnostic process and in evaluating the efficacy of medical and/or surgical treatment of orbital diseases. Tools designed to measure orbital volume with computed tomography (CT) often cannot be used with cone beam CT (CBCT) because of inferior tissue representation, although CBCT has the benefit of greater availability and lower patient radiation exposure. Therefore, a model-based segmentation technique is presented as a new method for measuring orbital volume and compared to alternative techniques.
  
  
  METHODS
  Both eyes from thirty subjects with no known orbital pathology who had undergone CBCT as a part of routine care were evaluated (n = 60 eyes). Orbital volume was measured with manual, atlas-based, and model-based segmentation methods. Volume measurements, volume determination time, and usability were compared between the three methods. Differences in means were tested for statistical significance using two-tailed Student's t tests.
  
  
  RESULTS
  Neither atlas-based (26.63 ± 3.15 mm(3)) nor model-based (26.87 ± 2.99 mm(3)) measurements were significantly different from manual volume measurements (26.65 ± 4.0 mm(3)). However, the time required to determine orbital volume was significantly longer for manual measurements (10.24 ± 1.21 min) than for atlas-based (6.96 ± 2.62 min, p < 0.001) or model-based (5.73 ± 1.12 min, p < 0.001) measurements.
  
  
  CONCLUSIONS
  All three orbital volume measurement methods examined can accurately measure orbital volume, although atlas-based and model-based methods seem to be more user-friendly and less time-consuming. The new model-based technique achieves fully automated segmentation results, whereas all atlas-based segmentations at least required manipulations to the anterior closing. Additionally, model-based segmentation can provide reliable orbital volume measurements when CT image quality is poor.
authors.affiliation: Department of Craniomaxillofacial Surgery, Hannover Medical School, Carl-Neubergstrasse 1, 30625, Hannover, Germany. m.e.h.wagner@icloud.com.
authors.forename: Maximilian E H
authors.initials: ME
authors.lastname: Wagner
authors.affiliation: Department of Craniomaxillofacial Surgery, Hannover Medical School, Carl-Neubergstrasse 1, 30625, Hannover, Germany.
authors.forename: Nils-Claudius
authors.initials: NC
authors.lastname: Gellrich
authors.affiliation: Institute for Man-Machine Communication, Leibniz University Hannover, Hannover, Germany.
authors.forename: Karl-Ingo
authors.initials: KI
authors.lastname: Friese
authors.affiliation: MIRALab, University of Geneva, Geneva, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Becker
authors.affiliation: Institute for Man-Machine Communication, Leibniz University Hannover, Hannover, Germany.
authors.forename: Franz-Erich
authors.initials: FE
authors.lastname: Wolter
authors.affiliation: Department of Craniomaxillofacial Surgery, Hannover Medical School, Carl-Neubergstrasse 1, 30625, Hannover, Germany.
authors.forename: Juergen T
authors.initials: JT
authors.lastname: Lichtenstein
authors.affiliation: Department of Craniomaxillofacial Surgery, Hannover Medical School, Carl-Neubergstrasse 1, 30625, Hannover, Germany.
authors.forename: Marcus
authors.initials: M
authors.lastname: Stoetzer
authors.affiliation: Department of Craniomaxillofacial Surgery, Hannover Medical School, Carl-Neubergstrasse 1, 30625, Hannover, Germany.
authors.forename: Majeed
authors.initials: M
authors.lastname: Rana
authors.affiliation: Department of Craniomaxillofacial Surgery, University Hospital Zürich, Zurich, Switzerland.
authors.forename: Harald
authors.initials: H
authors.lastname: Essig
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D009915:Orbit / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D009929:Organ Size / Q000502:physiology; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: Cone beam computed tomography; Model segmentation; Orbital volume; Pseudoforamina