The value of signal intensity ratios of orbital tissue to white matter of orbital MRI in evaluating graves' orbitopathy.

Absract: PURPOSE: To investigate the signal intensity ratio (SIR) of orbital tissue to white matter in orbital magnetic resonance imaging (MRI) for assessing graves' orbitopathy (GO).

Methods: This study enrolled a total of 42 patients (79 eyes) with GO as the GO group, 10 patients (20 eyes) diagnosed with graves' disease (GD) without orbitopathy during the same period as the GD group, and 23 normal individuals with negative MRI results and no thyroid or eye diseases as the healthy control (HC) group. The signal intensity of the lacrimal gland (LG), extraocular muscle (EOM), ipsilateral temporal muscle (TM), ramus mandibulae, and white matter (WM) on MRI images was measured. Patients in the GO group were categorized into active and inactive GO subgroups.

Results: The SIRs in the GO, GD, and HC groups showed significant differences. SIR-LG in relation to WM and SIR-EOMs in the GO group were significantly higher than those in the GD and HC groups. The SIRs in the active GO group were higher than those in the inactive GO group with significant differences, except for SIR-LG/TM. SIR-EOM/WM demonstrated higher accuracy than other SIRs in identifying GO activity. The area under the curve for SIR-EOM/WM was 0.81 (95% CI 0.71-0.91), with a sensitivity of 69.6%, specificity of 87.9%, and a cut-off value of 1.50.

Conclusion: SIR-LG/WM and SIR-EOMs are objective indicators for discriminating between GO and the other two groups. Furthermore, SIR-EOM/WM may serve as a simpler quantitative MRI biomarker for identifying GO activity and are worthy of clinical generalization.