Quantitative Analysis of Orbital Soft Tissues Using Three‐Dimensional Fast Spin Echo With 2‐Point Dixon‐Based Fat Suppression Sequence: Its Association With Methylprednisolone Pulse Therapy Treatment Efficacy in Thyroid‐Associated Ophthalmopathy

Background Three‐dimensional fast spin echo with 2‐point Dixon‐based fat suppression (3D‐FSE‐Dixon) sequence may assess volume and water fraction (WF) of orbit. Purpose To explore the association between 3D‐FSE‐Dixon based parameters and methylprednisolone pulse therapy (MPPT) efficacy in active moderate‐to‐severe thyroid‐associated ophthalmopathy (TAO). Study Type Retrospective. Population Fifty‐nine TAO patients (29 females, 30 males, 49.1 ± 10.9 years) were included: 26 (15 females, 11 males, 48.4 ± 11.1 years) showed improvement and 33 (14 females, 19 males, 49.6 ± 10.9 years) did not. Field Strength/Sequence 3D‐FSE‐Dixon sequence of orbits at 3 T. Assessment Manual segmentation delineated bony orbit (BO), whole orbit (WO), globe (GO), lacrimal gland (LG), and optic nerve (ON). Multi‐dimensional threshold (MDT) identified orbital fat (OF). Extraocular muscles (ETM) were obtained by subtracting other tissues from WO. WF was calculated from water and in‐phase images. Treatment efficacy, the clinical outcome, was assessed within 2 weeks after MPPT. Statistical Tests Unpaired t ‐test and Mann–Whitney U test compared normal and non‐normal data, respectively. Paired t ‐test analyzed parameter changes pre‐ and post‐MPPT. Multivariate logistic regression analysis identified factors independently associated with the efficacy of MPPT. Significance was set at P < 0.05. Results Responsive group showed significantly higher pre‐treatment WF (ETM, 0.86 ± 0.06 vs. 0.82 ± 0.07; OF, 0.21 ± 0.04 vs. 0.19 ± 0.02), with no difference in volume (OF: 21.34 ± 3.33 vs. 21.36 ± 3.46, P = 1.00; ETM: 13.48 ± 2.82 vs. 13.72 ± 3.45, P = 1.00) or volume ratio (OF/GO: 3.23 ± 0.50 vs. 3.26 ± 0.56, P = 1.00; ETM/GO: 2.06 ± 0.58 vs. 2.12 ± 0.64, P = 1.00). WF significantly decreased in responsive group (ETM, 0.86 ± 0.06 vs. 0.79 ± 0.05; OF, 0.21 ± 0.04 vs. 0.17 ± 0.03) but not decreased in unresponsive group (ETM, 0.81 ± 0.07 vs. 0.81 ± 0.07, P = 1.00; OF, 0.19 ± 0.02 vs. 0.190 ± 0.02, P = 1.00). ETM WF and disease duration can assess MPPT efficacy. Data Conclusion Higher ETM WF demonstrates better MPPT efficacy for TAO. Evidence Level 4 Technical Efficacy Stage 4