The study evaluated the efficacy of teprotumumab N01 (SYCUME®) injection in 22 Chinese patients (44 eyes) with thyroid disease (TED) who received full treatment between March and December 2025. After treatment, Hertel proptosis and Clinical Activity Score (CAS) were significantly reduced (both p < 0.001), as was proptosis measured by MRI (p < 0.001). Quantitative MRI showed a decrease in the maximum length and width of the inferior rectus muscle (IR) coronary cross-section (both p < 0.001), a decrease in ADC in the IR (p = 0.010), T1 and proton density in the IR (both p < 0.001), as well as an increase in fat fraction in the IR and orbital fat. Proptosis changes on MRI were associated with IR morphological changes, while CAS changes with IR and ADC morphological changes. Thyroid hormone levels remained stable, selected antibodies and IGF-1 changed significantly, GO-QOL improved (all p < 0.001). At the patient level, CAS changes were only associated with ΔTRAb and ΔIGF-1. IR and ADC morphological parameters from diffusion showed the most consistent associations with changes in proptosis and TED activity.