Habitat imaging based on water–fat separation for interpreting extraocular muscle heterogeneity in thyroid eye disease

Objective: The heterogeneity of extraocular muscles (EOMs) in thyroid eye disease (TED) correlates with response to intravenous glucocorticoid (IVGC) therapy but remains unquantified by current imaging. This study applied habitat imaging to characterize EOM heterogeneity and remodeling patterns. Methods: This retrospective study included 138 patients with active moderate-to-severe TED (84 responsive; 54 unresponsive), all undergoing water-fat separation imaging before and after IVGC therapy. Four EOM habitat subregions were defined using the Otsu method based on water and fat signal intensity (SI). Volume and volume percentage (VP), including their absolute (Δ) and relative (Δ%) changes post-therapy, were compared between groups. Univariate analysis compared habitat features, while binary logistic regression and receiver operating characteristic (ROC) curve analysis identified valuable parameters for evaluating therapeutic effect. Results: Habitat imaging identified edema (high SIwater and low SIfat) and myosteatosis (low SIwater and high SIfat) subregions. The responsive group exhibited a higher edema VP (32.64 vs 14.13%, P = 0.008) at baseline. After IVGC treatment, the responsive group had a significant decrease in edema VP (32.64 vs 9.85%, P < 0.001); both groups displayed increased myosteatosis, with more pronounced changes observed in the responders. The combination of Δ volume of myosteatosis region and Δ% volume of whole region demonstrated excellent discriminative ability (AUC = 0.86) with high sensitivity (93.75%) in treatment response assessment. Conclusions: Habitat imaging based on water-fat separation provides quantitative visualization of EOM pathological remodeling, establishing myosteatosis as an adjunctive biomarker for evaluating IVGC therapeutic response.