Reliability of Orbital MRI-Based Proptosis Measurement: A Multicenter Prospective Study

Accurate proptosis measurement change is critical for managing thyroid-associated ophthalmopathy (TAO), yet traditional Hertel exophthalmometry suffers from inter-observer inconsistency. This study aimed to investigate the efficacy of magnetic resonance imaging (MRI)-based proptosis measurement and developed an automated tool to enhance diagnostic reproducibility.

We retrospectively analyzed data from 250 patients with TAO prospectively enrolled at Center 1 between December 2023 and June 2025. Proptosis was independently measured by three radiologists (R1-R3) using both 2D and 3D MRI sequences; clinical measurements via Hertel exophthalmometry were obtained within one week for comparison. An automated measurement tool was developed and internally validated using manual annotations from the senior radiologist (R1) as the ground truth. To assess generalizability, the tool was externally validated on axial 2D MRI datasets from two independent cohorts: Center 2 (n = 65) and Center 3 (n = 48).

Orbital MRI-based measurements demonstrated excellent inter-observer agreement for both 2D (ICC: 0.948; 95% CI: 0.938-0.957) and 3D sequences (ICC: 0.954; 95% CI: 0.939-0.966). MRI findings showed a strong correlation with Hertel exophthalmometry (Spearman's ρ = 0.76-0.80). The automated tool maintained high performance across all cohorts, achieving concordance correlation coefficients (CCC) of 0.928-0.973 and intraclass correlation coefficients (ICC) of 0.916-0.973 in validation.

This MRI-based automated tool provides a reliable, complementary, and standardized alternative to Hertel exophthalmometry, particularly useful when clinical measurements are discordant or demand high precision for longitudinal monitoring. It demonstrated excellent accuracy, efficiency, and cross-center generalizability.