title: Orbital volume analysis: validation of a semi-automatic software segmentation method.
abstract: OBJECTIVE
  The purpose of this study was to validate a quick, accurate and reproducible (semi-) automatic software segmentation method to measure orbital volume in the unaffected bony orbit. Precise volume measurement of the orbital cavity is a useful addition to pre-operative planning and intraoperative navigation in orbital reconstruction.
  
  
  METHODS
  In 21 CT scans, one unaffected orbit was selected to compare manual segmentation (gold standard) with three segmentation methods using iPlan software (version 3.0.5; Brainlab, Feldkirchen, Germany): automatic (method A), automatic minus bone/air masks (method SA) and automatic minus masks followed by manual adjustments (method SAA). First, validation of the manual segmentation and a newly described method for the anterior boundary was performed. Subsequently the accuracy, reproducibility and time efficiency of the methods were examined. Measurements were performed by two observers.
  
  
  RESULTS
  The intraclass correlation for the interobserver agreement of the anterior boundary was 0.992, and the intraobserver and interobserver agreement for the manual segmentation were 0.997 and 0.994, respectively. Method A had an average volumetric difference of 0.49 cc (SD 0.74) in comparison with the gold standard; this was 0.24 cc (SD 0.27) for method SA and 0.86 cc (SD 0.27) for method SAA. The average time for each method was 38 (SD 5.4), 146 (SD 16.0) and 327 (SD 36.2) seconds per orbit.
  
  
  CONCLUSIONS
  The built-in automatic method A is quick, but suboptimal for clinical use. The newly developed method SA appears to be accurate, reproducible, quick and easy to use. Manual adjustments in method SAA are more time-consuming and do not improve volume accuracy. The largest volume discrepancy is located near the inferior orbital fissure.
authors.affiliation: Orbital Unit, Department of Oral and Maxillofacial Surgery, Academic Medical Centre, University of Amsterdam, Meibergdreef 9, 1105 AZ, Amsterdam, The Netherlands. j.jansen@amc.uva.nl.
authors.forename: Jesper
authors.initials: J
authors.lastname: Jansen
authors.affiliation: Orbital Unit, Department of Oral and Maxillofacial Surgery, Academic Medical Centre, University of Amsterdam, Meibergdreef 9, 1105 AZ, Amsterdam, The Netherlands.|Department of Oral and Maxillofacial Surgery, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors.forename: Ruud
authors.initials: R
authors.lastname: Schreurs
authors.affiliation: Orbital Unit, Department of Oral and Maxillofacial Surgery, Academic Medical Centre, University of Amsterdam, Meibergdreef 9, 1105 AZ, Amsterdam, The Netherlands.
authors.forename: Leander
authors.initials: L
authors.lastname: Dubois
authors.affiliation: Orbital Unit, Department of Oral and Maxillofacial Surgery, Academic Medical Centre, University of Amsterdam, Meibergdreef 9, 1105 AZ, Amsterdam, The Netherlands.|Department of Oral and Maxillofacial Surgery, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors.forename: Thomas J J
authors.initials: TJ
authors.lastname: Maal
authors.affiliation: Orbital Unit, Department of Oral and Maxillofacial Surgery, Academic Medical Centre, University of Amsterdam, Meibergdreef 9, 1105 AZ, Amsterdam, The Netherlands.
authors.forename: Peter J J
authors.initials: PJ
authors.lastname: Gooris
authors.affiliation: Orbital Unit, Department of Oral and Maxillofacial Surgery, Academic Medical Centre, University of Amsterdam, Meibergdreef 9, 1105 AZ, Amsterdam, The Netherlands.
authors.forename: Alfred G
authors.initials: AG
authors.lastname: Becking
mesh_terms: D005858:Germany; D006801:Humans; D009915:Orbit / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D009929:Organ Size / Q000502:physiology; D015203:Reproducibility of Results; D012984:Software; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: Orbital fractures; Orbital reconstruction; Orbital volume measurement; Pre-operative planning; Segmentation; Validation