Lateral rectus muscle as a new reference point in estimation of Graves’ ophthalmopathy activity

Background: The clinical progression of Grave’s ophthalmopathy (GO) is evaluated based on different parameters. Still, there is greater opportunity to carry out morphometric measurements, than to perform a quasi patho-physiological assessment.
The aims of this study were to evaluate the correlation of T2 relaxation time to muscle volume based on MR imaging and to investigate whether individual physical relativization of extraocular muscle volume significantly influences results.
Material/Methods: Ten controls and 20 patients underwent MR examination. Quantitative muscle assessment was carried out using a numerical segmentation image technique. T2 relaxation times were measured for each muscle, and a standardization algorithm was applied based on T2 relaxation time of ipsilateral frontal lobe white matter.
For each extraocular muscle, an absolute volume and a relative value were calculated by subtracting from each of these muscles’s volume from the volume of the lateral rectus muscle (RM) within the same orbital cavity.
Results: Highest correlation for relative T2 relaxation time and muscle volume was observed for inferior RM (value of r=0.520, which increased to r=0.660 after relativization). An increase in correlation for medial RM was also noted from r=0.473 to r=0.48. However, this correlation decreased slightly for superior RM from a value of r=0.597 to r=0.525.
Conclusions: Oculomotor muscle volume closely correlates to T2 relaxation time. Individual physical objectification significantly increases this correlation for MRM and IRM and consequently enables more precise use of muscle volume as an indicator of GO. Relativization is essential for data from both magnetic resonance and computer tomography studies.

Keywords: Graves’ ophthalmopathy, volume assessment, computer applications