title: Radiologic measurement of extraocular muscle volumes in patients with Graves' orbitopathy: a review and guideline.
abstract: OBJECTIVE
  To evaluate and compare techniques for extraocular muscle (EOM) volume measurement and to provide guidelines for future measurements.
  
  
  METHODS
  Systematic review.
  
  
  RESULTS
  Existing techniques used to measure extraocular muscle volumes on radiologic scans can be divided into manual outlining, computer assisted and automated segmentation. Both computed tomography (CT) and magnetic resonance (MR) image datasets can be used. On CT scans, one best measures muscle volume using region grow segmentation, accepting an overestimation of true volume by inevitable inclusion of non-muscular tissue. On high resolution MRI scans, single muscles can be outlined manually, but measurements include only part of the muscle due to poor tissue contrast at the orbital apex. Measurement errors can be reduced 3.5% by exact horizontal repositioning. A measured volume change of at least 6-17% is required to demonstrate a significant difference.
  
  
  CONCLUSIONS
  Currently the best choice for EOM volume measurements on CT images is computer assisted grey value segmentation and on MRI images is manual outlining of individual muscles. Because of the time required and the complexity of the measurements, present EOM volume measurement is as yet only suitable for research purposes.
authors.affiliation: Department of Ophthalmology, University Medical Center, Utrecht, The Netherlands. w.r.bijlsma@umcutrecht.nl
authors.forename: Ward R
authors.initials: WR
authors.lastname: Bijlsma
authors.forename: Maarten Ph
authors.initials: MP
authors.lastname: Mourits
mesh_terms: D006111:Graves Disease / Q000000981:diagnostic imaging* / Q000473:pathology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D009801:Oculomotor Muscles / Q000000981:diagnostic imaging* / Q000473:pathology; D014057:Tomography, X-Ray Computed