Multiparametric MRI for Diagnosing Dysthyroid Optic Neuropathy: Added Value of Magnetization Transfer Imaging

Abstract

Objective: To evaluate the ability of magnetization transfer imaging (MTI) to diagnose dysthyroid optic neuropathy (DON) and to establish the added value of MTI to conventional T2-weighted imaging (T2WI) and diffusion-weighted imaging (DWI).

Materials and methods: One hundred and forty-nine patients with thyroid-associated ophthalmopathy were included and divided into training (46 eyes with DON and 148 eyes without DON) and validation (20 eyes with DON and 64 eyes without DON) cohorts. The orbital magnetic resonance imaging (MRI) protocols included coronal MTI, fat-suppressed T2WI, and DWI. The minimum, mean, and maximum values of the magnetization transfer ratio (MTR), signal intensity ratio (SIR), apparent diffusion coefficient (ADC) of each optic nerve (ON), and modified muscle index (mMI) of each orbit were calculated and compared between the groups. Multi-variable logistic regression analysis was performed to identify the independent imaging predictors of DON. The performance of each imaging predictor and their combinations using a binary logistic regression model for diagnosing DON was evaluated using receiver operating characteristic (ROC) curve analysis.

Results: Eyes with DON exhibited significantly lower MTRs and ADCs of the ON, increased SIRs of the ON, and increased mMI. The MTR_mean of the ON, ADC_mean of the ON, and mMI were independent predictors of DON. The multi-variable model incorporating these three variables yielded an area under the ROC curve (AUC) of 0.946 and showed significantly higher diagnostic performance than MTR_mean (AUC = 0.831), ADC_mean (AUC = 0.738), or mMI (AUC = 0.862) alone in the training cohort (all P < 0.001). In the validation cohort, the multi-variable model achieved satisfactory diagnostic performance (AUC = 0.926).

Conclusion: MTI may be a useful non-invasive technique for diagnosing DON. MTR can provide additional value to conventional DWI in distinguishing patients with DON from those without DON.

Keywords: Dysthyroid optic neuropathy; Magnetic resonance imaging; Magnetization transfer; Optic nerve.