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Evaluating the Extraocular Muscle Changes in Thyroid Associated Ophthalmopathy using T1ρ―A Preliminary Study
Tan Guo1, Bing Wu2, Dandan Zheng2, Xiaoxiong Wang3, Xiaoxia Wang4, Yan Song1, and Min Chen1

1Radiology, Beijing Hospital, Beijing, People's Republic of China, 2MR Research China, GE Healthcare, Beijing, People's Republic of China, 3Ophthalmology, Beijing Hospital, 4Endocrinology, Beijing Hospital

Synopsis

This study is to investigate and compare the changes of extraocular muscles in patients with active thyroid associated ophthalmopathy shown by T1ρ and T2 maps. The superior differential ability of T1ρ comparing to the currently used T2 mapping is encouraging and the flexibility in exploring the different in spin lock frequencies would be promising tool in evaluating the extraocular muscle changes with thyroid associated ophthalmopathy.

Purpose

Thyroid associated ophthalmopathy (TAO) is an inflammatory autoimmune disorder characterized by lymphocyte infiltration of the orbit, producing glycosaminoglycan (GAG) in the extraocular muscles (EOM). GAG is a type of large hydrophilic molecules, and lead to an increase of the orbital volume and edema [1]. Orbital MRI can visualize the swollen EOMs in TAO. It was found that patients with active TAO feature hyperintense signal in T2 images of the EOMs coursed by edema. It was also reported that T2 relaxation times can be used to estimate the activity of TAO. However, the predictive values of T2 signal level and T2 relaxation rates for the assessment of activity is still under debtate [2]. T1ρ weighted imaging extract tissue information of large molecules via lower spin lock frequency, which may not be reflected in routine T1 and T2 imaging [3]. T1ρ may reflect the protein content and composition of tissue that may describe the pathological changes of TAO, however its use in TAO has not been reported. The aim of this study is to investigate and compare the changes of EOMs inTAO patients shown by T1ρ and T2 maps.

Methods

Nine clinically confirmed TAO patients and 6 normal control volunteers were recruited in this study. The clinical activity score (CAS) of all the patients were larger than 3 points indicating the activity of TAO. All the volunteers were asymptomatic and no prior eye disease. The patients and volunteers underwent MR examination including coronal T1ρ and T2 maps on a 3.0 T scanner (GE MR 750, GE Healthcare) with an 8 HD head coil. T1ρ images were obtained using spinlock techniques and the acquisition parameters were as follows: spin-lock time of 20/30/50/80 ms, spin-lock frequency of 100 Hz, TR/TE of 8000/minimum ms, FOV of 22×17.6 cm, matrix size of 256×256, slice thickness of 4 mm, skip of 0 mm. Parameters of the T2 imaging were: TR/TE of 1300/ 8/16/24/32/41/49/57/65 ms. Other parameters of the T2 sequence were the same as the T1ρ sequence. T1ρ and T2 maps were generated and the T1ρ and T2 values of the 4 rectus extraocular muscles (superior, inferior, medial and lateral rectus) were measured. The ROIs were placed on the largest cross section of the muscle belly of the 4 recti in coronal T1ρ and T2 images respectively. The T1ρ and T2 values of each rectus and the average value of 4 recti for each side of the eye were compared between the TAO group and normal control by independent samples t-test. SPSS 19.0 was used.

Results

In comparison with normal control, the T1ρ values of left inferior rectus (p=0.002), right inferior (p=0.001) and lateral rectus (p=0.01) were significant increased in TAO patients. The average T1ρ values of recti of both sides of eyes were also significantly higher in TAO patients than normal control (both p=0.002) (Fig 1). On the other hand, the T2 values of recti and average value of each eye did not show significant difference, except the right superior rectus (p=0.04), between the two groups (Fig 2). The T1ρ weighted images with a spin-lock time of 20 ms showed marked high signal intensity in the enlarged recti, while the T2 weighted images did not show obvious high signal in involved recti (Fig 3).

Discussion and Conclusion

As demonstrauted in this study, the T1ρ mapping of the recti can serve as a biomarker for diagnosis of TAO. When observing each rectus, the maximum difference of T1ρ as compared to the normal control occurs in both inferior rectus, which is consisted of the pathogenetic sequence. The inferior rectus is usually the first and the most severe EOM when TAO occurs[4]. However the increased T1ρ value contradicts with the known pathological changes of TAO. With a lower spin-locking frequency used, the large molecules can exchange the energy effectively, further to decrease the T1ρ relaxation time [5]. The high concentration of GAG may reduce the value of T1ρ as observed in previous work in articular cartilage [1,5]. As a result, decreased T1ρ is expected in TAO patients compared the healthy controls. The muscle edema caused by the deposition of GAG may be the cause. Small molecule like water may disturb the T1ρ relaxation process and lengthen the T1ρ value. Future study with a larer cohort would be needed for further clarification of this phenomenon. Nevertheless, the superior differential ability of T1ρ comparing to the currently used T2 mapping is encouraging and the flexibility in exploring the different in spin lock frequencies would be promising tool in evaluating the extraocular muscle changes with TAO.

Acknowledgements

No acknowledgement found.

References

[1] Tomoaki H, Nishida Y, Ohji M. Changes of orbital tissue volumes and proptosis in patients with thyroid extraocular muscle swelling after methylprednisolone pulse therapy. Jpn J Ophthalmol 2015; 59:430–435.

[2] Jiang H, Wang Z, Xian J, et al. Evaluation of rectus extraocular muscles using dynamic contrastenhanced MR imaging in patients with Graves’ ophthalmopathy for assessment of disease activity. Acta Radiologica 2012; 53:87-94.

[3]Stahl R, Luke A, Li X, et al. T1rho, T2 and focal knee cartilage abnormalities in physically active and sedentary healthy subjects versus early OA patients--a 3.0-Tesla MRI study. Eur Radiol 2009; 19:132-143.

[4] Yasuhiro N, Suna T, Bengt I, et al. MRI measurements of orbital tissues in dysthyroid ophthalmopathy. Graefes Arch Clin Exp Ophthalmol 2001; 239:824-831.

[5] Sridhar RC. T1ρ-weighted magnetic resonance imaging: Principles and diagnostic application Applied Radiology 2004; 32-43.

Figures

Figure 1 The comparison of T1ρ values of both side of the recti between the TAO group and normal control. * shows significant difference.

Figure 2 The comparison of T2 values of both side of the recti between the TAO group and normal control. * shows significant difference.

Figure 3 A TAO patient with enlarged extraocular musles. T1ρ weighted image shows marked high signal intensity in both side of lateral rectus. On the other hand, the signal of the swollen recti is less obvious in T2 weighted image compared with the relatively normal recti. The T1ρ value of the involved musles measured on T1ρ map is elevated, whereas the T2 value is not significantly increase.

Proc. Intl. Soc. Mag. Reson. Med. 25 (2017)
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