title: Morphometric parameters of extraocular rectus muscles evaluated by dynamic-multipositional magnetic resonance.
abstract: OBJECTIVE
  To establish normal values of morphologic parameters of extraocular rectus muscles visualized in different gaze positions by means of an accessible method of dynamic-multipositional magnetic resonance imaging (dmMRI).
  
  
  METHODS
  Twenty eyes of 10 healthy, orthotropic subjects were examined. A 1.5T scanner (Avanto) with standard head coil was used. The protocol of dmMRI included 6 gaze positions in 10° intervals in which 13-second, orbital, T2 sequences were performed in quasi-coronal plane. The measurements of extraocular rectus muscles shape, sectional area, and volume were obtained with use of ImageJ 1.38x (NIH) software.
  
  
  RESULTS
  Relative change in cross-sectional area between position of rest and gaze of action of each muscle appears to be significant just in the medial and posterior parts of their belly. The maximal cross-section area increases significantly when the muscle contracts (21% to 32% depending on the muscle). The superior rectus must be assessed along with levator palpebrae as the distinction between their bellies is difficult. Relative change in partial muscle volume on contraction ranged from 12.3% to 21.6% depending on the muscle. Muscle contraction results in more circular shape of its belly while relaxation is more of an ellipse.
  
  
  CONCLUSIONS
  Dynamic-multipositional MRI performed in the proposed manner is an accessible and repeatable method for visualization of extraocular rectus muscles. Assessment of morphometric parameters such as muscle shape, maximal cross-section area, and partial muscle volume is easy with digital imaging software.
authors.affiliation: Department of Ophthalmology, University Hospital Nr. 1, Medical University of Lodz, Lodz - Poland.
authors.forename: Piotr
authors.initials: P
authors.lastname: Loba
authors.forename: Anna
authors.initials: A
authors.lastname: Broniarczyk-Loba
authors.forename: Michal
authors.initials: M
authors.lastname: Pajak
authors.forename: Agata
authors.initials: A
authors.lastname: Majos
authors.forename: Ludomir
authors.initials: L
authors.lastname: Stefanczyk
authors.forename: Maria
authors.initials: M
authors.lastname: Orczykowska
mesh_terms: D000328:Adult; D019412:Anatomy, Cross-Sectional; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009801:Oculomotor Muscles / Q000033:anatomy & histology*; D012016:Reference Values