title: MRI measurements of orbital tissues in dysthyroid ophthalmopathy.
abstract: BACKGROUND
  Muscle volume investigation by different imaging techniques has proven useful in the diagnosis and follow up of treatment in dysthyroid ophthalmopathy. However, no study on muscle volume measurement by magnetic resonance imaging (MRI) has been done in this disease.
  
  
  METHODS
  Six patients with monocular or asymmetric binocular dysthyroid ophthalmopathy and eight controls were examined with orbital MRI using a surface coil. In the muscle volume study, 2 mm coronal slices were used for measuring the six extraocular muscles (EOM), i.e., medial rectus (MR), lateral rectus (LR) superior rectus (SR), inferior rectus (IR), superior oblique (SO), and inferior oblique (IO) muscles, as well as the orbital fatty tissue (OFT). In the muscle thickness study, 3 mm transverse and sagittal images were used for measuring the four rectus muscles during fixation in different gaze positions in horizontal and vertical planes.
  
  
  RESULTS
  In dysthyroid ophthalmopathy, the muscle volume of the six external eye muscles was significantly larger than in controls, except for the IO. The IR and MR showed the largest increase in muscle volume. The correlation between muscle thickness and different degrees of eye deflections was linear for all four rectus muscles both in patients and controls, and no significant differences in the slopes of the regression lines were found. The volume of OFT was significantly larger in patients than in controls, and the change in volume was larger than that of muscle volume.
  
  
  CONCLUSIONS
  MRI technique makes it possible to observe and evaluate quantitatively the volume of all six extraocular muscles and the orbital fatty tissue in dysthyroid ophthalmopathy. It also makes it possible to evaluate changes in morphology during eye muscle contraction.
authors.affiliation: Department of Ophthalmology, Shiga University of Medical Science, Tsukinowa, Otsu, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Nishida
authors.forename: S
authors.initials: S
authors.lastname: Tian
authors.forename: B
authors.initials: B
authors.lastname: Isberg
authors.forename: L
authors.initials: L
authors.lastname: Tallstedt
authors.forename: G
authors.initials: G
authors.lastname: Lennerstrand
mesh_terms: D000273:Adipose Tissue / Q000473:pathology*; D005260:Female; D006111:Graves Disease / Q000175:diagnosis*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015835:Ocular Motility Disorders / Q000175:diagnosis; D009801:Oculomotor Muscles / Q000473:pathology*; D009915:Orbit / Q000473:pathology*