Evaluation of rectus extraocular muscles using dynamic contrast-enhanced MR imaging in patients with Graves' ophthalmopathy for assessment of disease activity

Background: It is important to assess the activity of Graves' ophthalmopathy (GO) for planning optimal treatment strategy. Dynamic contrast-enhanced MR imaging (DCE-MRI) is a technique for assessment of microcirculation status. The correlation between disease activity and the microcirculation characteristics of extraocular muscles (EOMs) has been demonstrated in GO. Purpose: To investigate the changes of rectus EOMs in patients with active vs. inactive GO using DCE-MRI, and to evaluate the value of DCE-MRI in assessing the activity of GO. Material and Methods: Rectus EOMs of 20 healthy controls, 18 patients with active GO, and 16 patients with inactive GO were studied. The signal intensity (SI) of rectus EOMs on T2W images was evaluated. Regions of interest were placed on each rectus on DCE-MRI images. The DCE-MRI parameters including time to peak enhancement (Tpeak), enhancement ratio (ER), and wash-out ratio (WR) were calculated. Results: There were significant differences in SI and T-peak, ER and WR values among the three groups (P = 0.000). However, there was no significant difference in SI between the active and inactive groups (P = 0.07). T-peak values of each rectus were significantly increased in inactive group compared with the active group (P < 0.05). ER and WR values of the inferior rectus and WR values of the superior rectus in inactive group were significantly lower than those in active group (P < 0.05). There was significant correlation between clinical activity score (CAS) and minimum T-peak (minT(peak)), maximum ER (maxER) and maximum WR (maxWR) (P < 0.001). The cut-off values of minT(peak), maxER and maxWR were 156.98s, 1.31 and 13.50% respectively, giving positive predictive values of 68.00%, 88.90%, and 94.44% for the assessment of disease activity. Conclusion: DCE-MRI could demonstrate the microcirculatory changes of rectus EOMs in both active and inactive GO, and this MRI method is a useful tool in differentiating active from inactive GO.