Quantitative intravoxel incoherent motion diffusion-weighted imaging histogram profiling identifies diffusion biomarkers for active thyroid-associated ophthalmopathy

Intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) enables separation of pure molecular diffusion from microcirculatory perfusion. However, its application in thyroid-associated ophthalmopathy (TAO) remains limited. This study aimed to evaluate TAO activity using histogram analysis of turbo spin echo-based IVIM-DWI parameters. This retrospective study included 94 patients with TAO. IVIM-DWI-derived diffusion coefficient (D), pseudo-diffusion coefficient, perfusion fraction, and apparent diffusion coefficient (ADC) histogram parameters were measured for all extraocular muscles (EOMs) (medial, inferior, lateral, and superior) of both eyes. Further, the diagnostic efficacy of each parameter and changes in D pre- and post-treatment were determined. Most D histogram parameters were significantly higher in patients with active TAO than in those with inactive TAO. The 1st, 5th, 10th, 25th, 50th, and 75th percentiles and the minimum and mean in the D histograms correlated with parameters corresponding to the ADC. The highest 75th -percentile value among all EOMs in the D histogram demonstrated an area under the curve of 0.892, with an optimal cutoff of > 1.26 × 10⁻³ mm²/s. Its diagnostic performance was significantly superior to that of sex, age, or smoking status. However, the maximum, mean, standard deviation, variance, and 5th, 10th, 75th, 90th, 95th, and 99th percentiles of the D histograms were reduced post-treatment. D histogram analysis facilitates the clinical quantification of EOM edema and shows potential for assessing TAO activity and treatment efficacy. TAO was more likely to be active when the highest 75th -percentile value among all EOMs exceeded 1.26 × 10− 3 mm2/s.