Abstract
Background: Current magnetic resonance imaging (MRI) techniques for measuring extraocular muscle (EOM) volume
enlargement are not ideally suited for routine follow-up of Graves’ ophthalmopathy (GO) because the difficulty of
segmenting the muscles at the tendon insertion complicates and lengthens the study protocol.
Purpose: To measure the EOM sampled volume (SV) and assess its correlation with proptosis.
Material and Methods: A total of 37 patients with newly diagnosed GO underwent 3-T MRI scanning with iterative
decomposition of water and fat (IDEAL) sequences with and without contrast enhancement. In each patient, the three
largest contiguous coronal cross-sectional areas (CSA) on the EOM slices were segmented using a polygon selection tool
and then summed to compute the EOM-SV. Proptosis was evaluated with the Hertel index (HI). The relationships
between the HI value and EOM-SV and between HI and EOM-CSA were compared and assessed with Pearson’s correlation
coefficient and the univariate regression coefficient. Inter-observer and intra-observer variability were
calculated.
Results: HI showed a stronger correlation with EOM-SV (P<0.001; r¼0.712, r2¼0.507) than with EOM-CSA
(P<0.001; r¼0.645 and r2¼0.329). The intraclass correlation coefficient indicated that the inter-observer agreement
was high (0.998). The standard deviation between repeated measurements was 1.9–5.3%.
Conclusion: IDEAL sequences allow for the measurement EOM-SV both on non-contrast and contrast-enhanced scans.
EOM-SV predicts proptosis more accurately than does EOM-CSA. The measurement of EOM-SV is practical and
reproducible. EOM-SV changes of 3.5–8.3% can be assumed to reflect true volume changes
