Thyroid-associated ophthalmopathy (TAO) is an autoimmune disease associated with thyroid disease, with symptoms that may include upper lid retraction (ULR), diplopia, and vision loss, seriously affecting patients’ quality of life (1–5). According to the latest guidelines for TAO management (6, 7), the optimal treatment strategy primarily relies on the Clinical Activity Score (CAS) and the European Group on Graves’ orbitopathy (EUGOGO) classification of severity. However, the subjective nature and limited comparability of CAS and the EUGOGO classification of severity pose challenges in accurately reflecting the size, morphology, and internal changes of orbital tissue (6). Consequently, the objective assessment of TAO becomes a challenging task, emphasizing the crucial role of objective indicators in evaluating TAO.

ULR stands out as a pivotal diagnostic criterion and common ocular manifestation in TAO, serving as an important indicator for assessing the disease’s severity (8, 9). Previous investigation indicates that immune-reactive inflammation of the levator palpebrae superioris (LPS) contributes significantly to ULR (10, 11). Therefore, gaining a comprehensive understanding of LPS characteristics and its relationship with disease progression is essential for the objective evaluation of TAO. Direct observation of LPS in clinical practice is challenging. Magnetic resonance imaging (MRI) is a fundamental diagnostic tool utilized in clinical settings of TAO, providing visualization of orbital tissues (including LPS) and monitoring dynamic changes in orbital tissues (12–16). Despite numerous studies using MRI in TAO, there are still considerable debates about the evaluative capabilities of various MRI techniques in TAO (17, 18). Our previous research indicates that the Dixon technique has significant advantages in assessing TAO (19).

The Dixon-T2WI sequence is a fat-suppression technique based on chemical shift analysis, allowing effective separation of water and fat (18–20). Compared to inversion recovery-based fat-suppression sequences, Dixon-T2WI is less susceptible to magnetic susceptibility artifact (21). The short acquisition duration is attributed to a high chemical shift at high field (22). These advantages make Dixon-T2WI well-suited for head, neck, and orbital imaging (23), providing a more precise visualization of subtle inflammatory changes within LPS (24). Previous studies have suggested the utility of measuring the maximum thickness of LPS (LPS_T) and signal intensity ratio (LPS_SIR) between the muscle and ipsilateral brain white matter in MRI sequences as crucial indicators for evaluating TAO (25, 26). However, limited research has employed Dixon-T2WI technology for quantitative assessment of its activity and severity, providing numerical cutoff points.

Our study utilized Dixon-T2WI to investigate the relationship between LPS and ULR, CAS, and the EUGOGO classification of severity in TAO, aiming to assess the diagnostic value of LPS in TAO and evaluate its condition.

This study obtained approval from the Institutional Review Board (IRB: KYLS20220723), and informed consent was obtained from all participants. The study focused on a single orbit. Retrospective data were collected from 280 patients who underwent orbital MRI at our hospital from October 2020 to November 2023. The indications for orbital MRI in patients are as follows: (a) when clinicians initially suspect a patient has TAO, performing orbital MRI helps distinguish it from other orbital diseases; (b) when clinicians have made a provisional diagnosis of TAO in a patient, conducting orbital MRI helps determine the detailed severity and extent of the disease; (c) when clinicians have confirmed a diagnosis of TAO in a patient, performing orbital MRI is used to regularly monitor the progression of the disease; and (d) orbital MRI are performed on TAO patients after treatment to evaluate treatment efficacy. The inclusion criteria for affected eyes in the TAO group were as follows: (a) meet the diagnostic criteria for TAO according to Bartley’s criteria (8), and (b) complete clinical data or MRI image data. The exclusion criteria for affected eyes in the TAO group were as follows: (a) history of previous eye surgery or trauma; (b) prior history of orbital radiation therapy; and (c) large MRI image artifacts and poor image quality. A total of 329 eyes were excluded based on the inclusion and exclusion criteria, leaving 231 eyes (119 patients) in the TAO group. Concurrently, 78 eyes (39 volunteers) were recruited as the normal group. The inclusion criteria for the normal group were as follows: (a) the absence of thyroid eye disease and other orbital diseases; (b) no history of previous eye surgery or trauma; and (c) complete MRI data and good image quality ( Supplementary Figure S1 ). Subjects underwent orbital examination with a 3-Tesla Skyra MRI System (Siemens Healthcare, Erlangen, Germany) within 7 days of the ophthalmic examination. Clinical information of the subjects was collected, including age, gender, smoking history, duration of TAO, thyroid-stimulating hormone (TSH), free thyroxine (FT4), thyrotropin receptor-stimulating antibody (TSAb), ULR, diplopia, treatment, exophthalmos by Hertel, CAS, the EUGOGO classification of severity, and the degree of ULR. Subject demographics are shown in Table 1 .

In this study, we provided a clinical study with 309 eyes (231 TAO eyes and 78 normal eyes) to assess the diagnostic value of LPS_T and LPS_SIR in TAO. The results illustrate that both indicators exhibit diagnostic performance, underscoring their significance in TAO evaluation. Furthermore, distinguishing itself from existing domestic and international studies, this study uniquely evaluated TAO’s activity and severity using measurements of LPS_T and LPS_SIR derived from Dixon-T2WI sequences. The results indicate that this method is straightforward, quantitative, highly accurate in assessment, and provides intergroup cutoff. This implies that LPS_T and LPS_SIR can serve as objective imaging indicators to assist in the diagnosis of TAO. Moreover, they can also serve as objective quantitative indicators to assist in assessing the condition, providing evidence for further exploration of imaging criteria to evaluate and predict treatment efficacy.

In this study, LPS_SIR represents the degree of inflammatory edema in the LPS, while LPS_T signifies the extent of its swelling (29). The results indicated that both LPS_T and LPS_SIR were significantly higher in the TAO group compared to the normal group, which is consistent with the findings of Duan et al (25). Furthermore, among TAO eyes, those with ULR ≥ 2 mm exhibited significantly higher values of LPS_T and LPS_SIR compared to those with ULR < 2 mm. This suggests that these two features can reflect the condition of eyelid retraction and provide imaging support for the diagnosis and treatment of TAO. We proposed a cutoff for LPS_T and LPS_SIR to diagnose TAO. We found that a cutoff of 1.505 mm for LPS_T yielded the highest sensitivity and specificity for TAO diagnosis. Likewise, for LPS_SIR, the identified cutoff was 1.170, also indicating the highest sensitivity and specificity. Therefore, LPS_T and LPS_SIR have excellent diagnostic value and are important indicators in diagnosing TAO.

Our research findings further validate the positive correlations between LPS_T and LPS_SIR with CAS and the EUGOGO classification of severity. Moreover, both of these features exhibit significant increases in the eyes of patients with active and moderate-to-severe TAO, thereby showing the diagnostic capability of the Dixon-T2WI sequence in assessing orbital inflammation. Based on ROC analysis, we found that both LPS_T and LPS_SIR demonstrated good performance for assessing the activity and severity of TAO. Among them, LPS_SIR exhibited the best diagnostic performance with the highest AUC value. Thus, we propose a cutoff of 1.129 for LPS_SIR to diagnose the active TAO. Similarly, a cutoff value of 1.197 for LPS_SIR was proposed to diagnose the moderate-to-severe and above. However, the diagnostic performance of LPS_T appears to have acceptable sensitivity but low specificity. The following are the possible reasons for this: (1) insufficient sample size may lead to biased errors; (2) assessment of TAO based solely on MRI features of LPS may not provide a comprehensive evaluation and would benefit from incorporating multiple variables; and (3) the use of CAS and the EUGOGO classification of severity as indicators for disease assessment in determining the cutoff using ROC analysis, which is subjective and has insufficient sensitivity. This also suggests that using CAS and the EUGOGO classification of severity alone may not fully reflect the condition of TAO.

This study has limitations. Firstly, it is a retrospective, single-center study, which introduces inherent bias. Secondly, the sample size of the sight-threatening group was relatively small, which may not be representative of the whole population. Additionally, TAO is a complex disease involving multiple factors, and its clinical manifestations are multiple factors. It is difficult to comprehensively evaluate TAO based on MRI features of LPS alone, and it is necessary to combine multiple objective indicators to evaluate TAO clinically. Finally, in the future, a larger prospective cohort should be conducted to further validate the quantitative value of the LPS thickness and SIR in clinical practice.

In conclusion, the maximum thickness and SIR of LPS can serve as objective indicators to assist in the diagnosis and quantitative evaluation of TAO, alleviating the limitations of CAS and EUGOGO classifications, which suffer from pronounced subjectivity and limited comparability. These indicators provide a research basis for exploring imaging criteria in the next step for evaluating and predicting efficacy.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving humans were approved by the ethical review boards of Shunde Hospital of Southern Medical University (KYLS20220723). The studies were conducted in accordance with the local legislation and institutional requirements. Written informed consent for participation was not required from the participants or the participants' legal guardians/next of kin in accordance with the national legislation and institutional requirements

DL: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Software, Validation, Visualization, Writing – original draft. YD: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing – original draft. KH: Data curation, Formal analysis, Software, Investigation, Writing – original draft. CS: Data curation, Software, Methodology, Investigation, Writing – original draft. YO: Data curation, Formal analysis, Investigation, Writing – original draft. XL: Data curation, Methodology, Investigation, Writing – original draft. JS: Conceptualization, Supervision, Writing – review & editing. HC: Funding acquisition, Project administration, Resources, Supervision, Writing – review & editing. All authors contributed to the article and approved the submitted version.