Original Investigation

Quantitative Assessment of Optic Nerve With Diffusion Tensor Imaging in Patients With Thyroid Orbitopathy Berna Özkan, MD*, Yonca Anik, MD†, Büşra Katre, MD*, Özgül Altıntaş, MD*, Mehmet Gençtürk, MD†, and Nurşen Yüksel, MD* *Department of Ophthalmology, Kocaeli University, Faculty of Medicine, Izmit, Turkey; and †Department of Radiology, Kocaeli University, Faculty of Medicine, Izmit, Turkey

Purpose: To detect abnormalities of the optic nerve in patients with thyroid orbitopathy using diffusion tensor MRI. Methods: Twenty-eight patients with Graves orbitopathy prospectively underwent diffusion tensor imaging scanning. A full ophthalmic examination including visual acuity, intraocular pressure, fundoscopy, and visual field analysis was performed. Clinical activity scores were also calculated. Fractional anisotropy (FA) and mean diffusivity values of the patients were compared with age and sex-matched healthy control subjects. Results: The mean FA values were decreased and mean diffusivity values were increased significantly in patients with Graves orbitopathy compared with the control subjects (p < 0.001). There was a strong reverse correlation between the FA levels and the visual fields in 4 quadrants of the optic nerve. In addition, there was a strong correlation between the degree of proptosis and the FA values in both eyes. The mean diffusivity levels were also correlated with changes in the visual field and the degree of proptosis. Conclusion: FA and mean diffusivity levels measured with the diffusion tensor imaging of the thyroid orbitopathy patients were affected. The changes in diffusion tensor imaging were also correlated with the ophthalmologic tests of the patients. (Ophthal Plast Reconstr Surg 2015;31:391–395)

about water diffusion within white mater structures.5 Tissue diffusion properties can be assessed by means of two postprocessed indices: mean diffusivity (MD) and fractional anisotropy (FA). MD represents the magnitude of the diffusion tensor and is a parameter of demyelination or glia cell impairment,6 whereas FA measures the orientation coherence of diffusion and provides information about the fiber integrity.7 Correlation between DTI-derived FA values of the optic nerves and visual parameters was reported recently.8–13 Filippi et al.8 showed that FA was decreased and MD was increased in the optic nerves and radiations of children with neurofibromatosis Type-1 who had gliomas along the optic pathway (optic nerve gliomas, chiasmatic gliomas, or unidentified glioma objects). In another study, Li et al.9 evaluated patients with indirect traumatic optic neuropathy and grouped them according to the duration after trauma. They found that FA values were progressively decreasing and MD values were progressively increasing in patients with optic nerve trauma with longer duration. DTI parameters could also be affected by glaucomatous optic nerve damage. The changes in FA and MD were found to be correlated with the visual field changes, central macular function, and retinal nerve fiber thickness in patients with glaucoma.10 The aim of this study was to evaluate whether DTI can detect the effects of orbital complications of GO on the optic nerve.

MATERIALS AND METHODS

G

raves orbitopathy (GO) is an autoimmune disorder that affects orbital tissues and is characterized with inflammation, edema, and fibrosis. The disease results with complications such as eyelid retraction, proptosis, extraocular muscle involvement, and optic neuropathy. To evaluate the effect of the disease on orbital tissues in patients with GO, different imaging techniques have been proposed. Ultrasound enables differential diagnosis of proptosis and reveals existing inflammation. CT scan shows muscle thickness, diagnoses compressive optic neuropathy, and defines the degree of proptosis. MRI reveals the activity of the muscles and the increase in orbital fat.1–4 Diffusion tensor imaging (DTI) is a noninvasive MRI technique, which is sensitive to the microscopic motion of the water molecules in tissue and provides quantitative information Accepted for publication October 20, 2014. The authors have no financial or proprietary interest in any product mentioned in the article. Address correspondence and reprint requests to Berna Özkan, Ağaoğlu My Village, Parsel 2, A12/1 Sancaktepe, 34885, İstanbul, Turkey. E-mail: [email protected] DOI: 10.1097/IOP.0000000000000359

Ophthal Plast Reconstr Surg, Vol. 31, No. 5, 2015

The local ethical committee approved the study, and informed consent was obtained from all subjects. Patient Demographics. Twenty-eight consecutive cases demonstrating GO (20 women and 8 men) and 27 control subjects were included in the study. All patients were Caucasian. The mean age of the patients was 45.96 ± 13.75 (25–68). Ophthalmologic Assessments. A full ophthalmic examination including visual acuity, intraocular pressure, fundoscopy, and visual field analysis was performed in all cases. Axial proptosis was assessed with both Hertel exophthalmometry and MRI. Visual field analysis was performed with the 30-2 testing protocol standard SITA on the Humphrey Visual Field Analyzer (Carl ZeissHumphrey Systems, Dublin, CA). In this automated test, the patient is asked to fixate at the central point with each eye while light of variable intensity is flashed in the peripheral field of vision. The patient is required to acknowledge the flashing light by pressing a button. The Humphrey field analyzer provides a quantitative measure of visual field in each of the 4 quadrants, and the average reading for visual field in each quadrant of the eyes was recorded. The learning curve effect was taken into consideration

391

Copyright © 2014 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc. Unauthorized reproduction of this article is prohibited.

Ophthal Plast Reconstr Surg, Vol. 31, No. 5, 2015

B. Özkan et al.

FIG. 1. ROI was placed on the midpoint of the orbital segment of optic nerve. After finding the exact midpoint by using the software, ROIs were placed at 4 quadrants as nasal superior (red), nasal inferior (yellow), temporal superior (blue), and temporal inferior (green) quadrants of the optic nerve. when performing the test. All patients in the GO group consisted of those who were seen routinely in follow-up visits. For this reason, they had multiple visual field examinations performed at each visit. New patients admitted to the clinic were given a second visual field examination 15 days after the first one to rule out any potential learning effect. The disease activity of the cases was evaluated by using the clinical activity score (CAS). The CAS consists of 7 items: spontaneous pain behind the globe, pain on attempted up gaze, redness of the conjunctiva, redness of the eyelid, chemosis, swelling of the caruncle, and eyelid swelling. A CAS score >3 was classified as active disease. MRI Technique and Data Analysis. MR examinations were performed with 3T scanner (Philips Achieva Intera Release Eindhoven, The Netherlands) with a 139-mT/m maximum gradient strength and a 346-mT/M/ms slew rate using an 8-channel phased array head coil. The patients were placed in supine position. The conventional orbital imaging protocol included coronal and axial T2-weighted and T1-weighted images. For DTI, single-shot echo-planar imaging sequence (4805/59; field of view, 250 × 250; section thickness, 2 mm with no intersection gap) with a maximal b value of 1,000 s/mm2 along 15 directions and a baseline image with no diffusion weighting (b = 0) were acquired. One radiologist, who was masked to the patients’ clinical data, processed the data on a separate workstation (Release 2.5.3.0 2007-12-03 Philips medical Systems Netherlands B.V). The measurements were taken

with the region of interest (ROI) method. To ensure the correct placement of the ROIs, DTI tractography by the FACT (fiber assignment by continuous tracking) method was used. ROI was placed on the midpoint of orbital segment of the optic nerve. To ensure the exact point; midpoint on axial images was determined, and by the help of localizer provided by software, the point was fixed on coronal images, and then ROIs were placed at 4 quadrants as nasal superior, nasal inferior, temporal superior, and temporal inferior (Fig. 1). ROIs were than copied to DTI images and FA and MD measurements were performed. These measurements were repeated 3 times for each measurement and mean values were calculated and statistical analysis was performed. ROI diameter was set as 0.8 mm. Later, FA and MD values in 4 quadrants (upper temporal, lower temporal, upper nasal, and lower nasal) of the optic nerves were measured (Figs. 2 and 3). Upper temporal ROI is correlated with the lower nasal visual field, lower temporal ROI is correlated with the upper nasal visual field, upper nasal ROI is correlated with the lower temporal ROI, and lower nasal ROI is correlated with the upper temporal visual field. Statistical Analysis. Statistical analysis was performed with SPSS 13. Degree of proptosis, visual field analysis in 4 quadrants, and optic nerve tractography with FA and MD measurements were considered. Paired t test was used to compare FA and MD levels of optic nerve between study and control groups. A value of p < 0.05 was considered statistically significant. Pearson correlation test was used in correlation of FA and MD levels with proptosis and visual field analysis.

RESULTS Age distribution among GO and the healthy volunteer groups was found to be homogenous. Most of the patients’ visual acuity was 1.0 (20/20), measured by Snellen chart (87.5%). Only 7 eyes (of 4 patients) had decreased visual acuity. However, none of them was related to GO. None of the patients had dyschromatopsia, relative afferent pupillary defect, or optic disc edema. CAS of 22 patients (78.5%) were 2 or lower than 2. All the patients were endocrinologically stable. The demographic and clinic characteristics of the patients are shown in Table 1. The FA levels at 4 quadrants of both optic nerves in GO patients were decreased significantly compared with that of the healthy controls. In contrast to the FA levels, the MD levels were statistically significantly increased. Comparison of FA and MD levels of both eyes among GO and the control group revealed significance at all quadrants; p values are given in Table 2. Visual field deficits in decibels were correlated to these corresponding visual field regions on DTI. There was a strong reverse

FIG. 2.  Fiber tractography of the optic nerves is shown on 3D colored FA maps derived from DTI. The yellow lines shows the fiber tract of the optic nerve.

392

© 2014 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc.

Copyright © 2014 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc. Unauthorized reproduction of this article is prohibited.

Ophthal Plast Reconstr Surg, Vol. 31, No. 5, 2015

Quantitative Assessment of Optic Nerve With DTI

FIG. 3.  Fiber tracts obtained following placement of ROIs for FA and MD measurements are shown on coronal and 3 orthogonal T2-weighted images. Each color shows different quadrant of the DTI measurement. (RED: superior nasal, GREEN: inferior nasal, PINK: superior temporal, BLUE: inferior temporal). correlation between the FA levels and the mean deviation of the visual fields in 4 quadrants of the optic nerve. There was also a weak linear correlation between the MD levels and the visual fields in 4 quadrants of the optic nerve. Detailed p and r values are given in Table 3. The FA and MD levels were correlated with proptosis measured with both Hertel exophthalmometry and MRI. Independent t test revealed no significance among Hertel and MRI proptosis measurements (OD p = 0.9, OS = 0.88). In Hertel exophthalmometry measurements: Pearson correlation results revealed a strong correlation between the degree of proptosis and the FA values in both eyes (OD: p < 0.0001, r = −0.744, OS: p < 0.0001, r = −0.752) (Fig. 4). There was a medium correlation between the degree of proptosis and the MD values of the OD (p = 0.003, r = −0.542). There was a medium correlation between the degree of proptosis and the MD values of the OS (p = 0.002, r = −0.573). In MRI measurements: similarly, there was a strong correlation between the degree of proptosis and FA levels in both eyes (OD: p − 0.0001, r = −0.972, OS: p ≤ 0.0001, r = −0.861).

focus, double-vision, retro-orbital pain, and blurred vision, it can be difficult to diagnose optic neuropathy in some cases. DTI is an effective method that shows the changes in optic nerve. Nucci et al.15 found that DTI parameters of the axonal architecture of the optic nerve show good correlation with morphologic features of the optic nerve head and retinal nerve

DISCUSSION

10 8 4 3 1 2 0 0

Diffusion is the random motion of molecules. Brain diffusion can occur in any direction, but it occurs preferentially parallel to the orientation of axons. DTI is an extension of diffusion weighted imaging in which ≥6 measurements probe diffusion in different directions. Any disruption to white matter tracts or in change in axonal membrane permeability would be expected to change DTI parameters and in particular lead to an increase in the MD, a measure of average molecular motion, and also to a decrease in FA, a measure of the preponderance of diffusion direction.12 GO is an inflammatory and autoimmune disorder of the orbit. The immune basis of the disease is characterized by a perivascular and diffuse infiltration of CD4+ and CD8+ T cells, B cells, plasma cells, and macrophages.14 Orbital fibroblasts are believed to play a crucial role in the pathogenesis by their ability to produce hydrophilic glycosaminoglycans that result in retention of fluid and edematous swelling of orbital tissues. Swelling of the orbital tissues may lead to proptosis and compressive optic neuropathy. Dysthyroid optic neuropathy can result in permanent and irreversible severe visual loss. Dysthyroid optic neuropathy might be diagnosed by clinical examination, changes in visual field examination, or radiologic findings. However, if the patient has multiple ocular pathologies related to GO such as excessive tearing, foreign body sensation, swelling of eyelids, inability to

TABLE 1.  Demographic and clinic characteristics of patients Characteristic Mean age Gender  Male  Female Duration of thyroid disease Clinic activity score:  0  1  2  3  4  5  6  7 Thyroid function:  TSH  FT3  FT4 Visual acuity:  1.0  0.8  0.7  0.6  0.5  0.4 Dyschromatopsia Relative afferent pupillary defect Optic disc edema

© 2014 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc.

n

Mean ± SE (range) 45.96 ± 13.75 (25–68) years

20 8 5.18 ± 1.02 (1–17) years

2.12 ± 0.47 (0.01–5.77) 2.97 ± 0.15(2.27–3.80) 1.05 ± 0.71(0.80–1.50) 49 1 2 2 1 1 0 0 0

393

Copyright © 2014 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc. Unauthorized reproduction of this article is prohibited.

Ophthal Plast Reconstr Surg, Vol. 31, No. 5, 2015

B. Özkan et al.

TABLE 2.  The FA and MD levels of the patients were compared with the controls and statistically significant difference was found in all quadrants of the optic nerve in both eyes

P (FA) P (MD)

Right upper temporal

Right upper nasal

Right lower temporal

Right lower nasal

Left upper temporal

Left upper nasal

Left lower temporal

Left lower nasal

0.004 0.014

0.006 0.022

0.003 0.018

0.009 0.035

0.001 0.021

0.001 0.022

0.004 0.026

0.003 0.019

p < 0.05 was considered statistically significant.

fiber layer documented with scanning laser polarimetry, optical coherence tomography, and Heidelberg Retinal Tomograph III. Anık et al.16 studied quantitative assessment of early visual recovery in patients with pituitary macroadenomas. They reported a correlation between FA values of the optic nerves and visual parameters and concluded that DTI assessments of the affected sides with FA and MD values may help to estimate the response of visual improvement to the surgical therapy in the early postoperative period. In a recent study, Engelhorn et al.13 evaluated the DTI MRI of the patients with glaucoma. Similar to our study, they found that FA of the patients was significantly decreased and MD levels of the patients were significantly higher compared with the control group. In addition, they found a good correlation between the increase in MD and the decrease in FA and the severity of the optic nerve atrophy and the retinal impairment quantified with established ophthalmologic tests. Optic neuritis in patients with multiple sclerosis was also found related with the changes in DTI. Naismith et al.17 found that increased optic nerve radial diffusivity was associated with a proportional decline in vision in patients who had optic neuritis at least 6 months prior. In their study, they showed that radial diffusivity differentiated healthy controls from both clinically affected nerves and unaffected fellow nerves after optic neuritis. In addition, radial diffusivity discriminated the unaffected fellow nerves from affected nerves in all visual outcome categories (normal recovery, mild impairment, profound visual loss). Radial diffusivity also discriminated nerves with recovery to normal from mild visual impairment, and those with mild impairment to profound loss. This may show that DTI is a sensitive method in evaluating the changes in optic nerve after optic neuritis. However, it is not a specific method. DTI measurements might change in any disease that affects the optic nerve. But it could discriminate the severity of the disease. This study shows that DTI MRI is an effective method in demonstrating the changes in optic nerve, even before it is clinically evident. In our study, none of our patients demonstrated clinical TABLE 3.  There was a strong reverse correlation between the FA levels and the visual fields in 4 quadrants of the optic nerve FA

Right upper temporal Right upper nasal Right lower temporal Right lower nasal Left upper temporal Left upper nasal Left lower temporal Left lower nasal

MD

p

r

p

r

0.011 0.009 0.006 0.008 0.004 0.016 0.005 0.009

−0.654 −0.679 −0.598 −0.565 −0.721 −0.618 −0.583 −0.596

0.041 0.028 0.042 0.038 0.023 0.039 0.047 0.048

0.317 0.298 0.324 0.301 0.389 0.363 0.356 0.329

There was also a weak linear correlation between the MD levels and the visual fields in 4 quadrants of the optic nerve.

394

symptoms of optic neuropathy. But the FA and MD levels were affected. DTI has demonstrated good correlation to histopathology in both animal models and humans.18,19 DTI MRI measuring water diffusion parallel and perpendicular to axonal tracts has been shown to be specific to axonal and myelin damage in mouse models of optic nerve injury. Extensive injury due to loss of myelin and axons leads to decreased anisotropy. This results in increased diffusion perpendicular to the white matter tract, increased overall diffusivity (MD), and decreased tissue directionality (FA).17 In GO orbital soft tissue inflammation, increase of orbital volume with proptosis might cause optic neuropathy. Inflammatory phase is self-limiting but it may relapse, in most cases, owing to insufficiently controlled thyroid disease, but also independently. Dynamic nature of the inflammation creates a challenging situation for monitoring the patient, especially timing of the optic nerve compression and whether it causes optic nerve injury is not always known. This study suggests that DTI MRI might show the optic nerve injury in GO, even though it was not clinically evident. GO may progress to clinically evident optic neuropathy in 3% to 5% of patients. This complication presents with sudden or progressive decrease in visual acuity.20 Early optic nerve dysfunction in the absence of decreased visual acuity may be revealed with visual field examination.21 However, visual field examination is a partially subjective examination, which can be affected by different factors such as patient’s cooperation, refraction or even presence of dry eye. To obtain an acceptable visual field examination, patients might perform the examination several times. The strong reverse correlation between the FA levels and the visual field evaluations and the linear correlation between the MD levels and visual field evaluations suggest that DTI MRI can detect the functional loss as effective as visual field examination. We also found that there was a strong correlation between the amount of proptosis and FA levels of the patients. Proptosis is the second most common finding in GO.17 Normally, 1/3 of the globe is located behind the interzygomatic line and Hertel index of ≥22 mm is abnormal, although there are known ethnic differences. Kirsch et al.22 pointed out that proptosis can be measured precisely on axial T1 images of MRI compared with the clinically measured Hertel index. We believe that with the help of the diffusion tensor images of the MRI, we cannot only assess the degree of proptosis in our patients but also evaluate whether the optic nerve was affected from the disease. One of the limitations of our study was our patients did not have a wide range of CAS. Most of the patients had CAS that was equal to or smaller than 2. Because our patients had similar clinical activity, we could not correlate the change in DTI MRI parameters and the CAS. For this reason, we could not comment on the correlation of DTI MRI parameters with the clinical activity. Another limitation of our study was none of our patients had any symptom of dysthyroid optic neuropathy. Our study shows that DTI MRI might be effective in discriminating the early changes in optic nerve in GO. However, the changes

© 2014 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc.

Copyright © 2014 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc. Unauthorized reproduction of this article is prohibited.

Ophthal Plast Reconstr Surg, Vol. 31, No. 5, 2015

Quantitative Assessment of Optic Nerve With DTI

FIG. 4.  The charts showing the correlation between the degree of proptosis and FA. A, OD. B, OS.

in DTI MRI might be progressive in patients with severe optic neuropathy. We believe that a larger group of study subjects with different clinical activities and optic neuropathy severity might provide a better understanding of the disease. In the future, DTI MRI might help us discriminate the severity of the disease. In addition, it might be a guide for the treatment of the patients, because the changes in the optic nerve could be detected earlier and the disease could be treated according to its severity. In conclusion, we found that MD and FA values of the optic nerve can be affected in GO. Further investigations with larger study groups should be performed to show the relationship between the DTI MRI measurements, the activity of GO, and dysthyroid optic neuropathy.

REFERENCES 1. Prummel MF, Suschulten MSA, Wersinga WM, et al. A new ultrasonographic method to detect disease activity and predict response to immunosuppressive treatment in Graves’ ophthalmopathy. Ophthalmology 1993;199:556–61. 2. Goodall KL, Jackson A, Leatherbarrow B, et al. Enlargement of the tensor intermuscularis muscle in Graves’ ophthalmopathy. A computed tomographic and magnetic resonance imaging study. Arch Ophthalmol 1995;113:1286–9. 3. Polito E, Leccisotti A. MRI in Graves orbitopathy: recognition of enlarged muscles and prediction of steroid response. Ophthalmologica 1995;209:182–6. 4. Lennerstrand G, Tian S, Isberg B, et al. Magnetic resonance imaging and ultrasound measurements of extraocular muscles in thyroid-associated ophthalmopathy at different stages of the disease. Acta Ophthalmol Scand 2007;85:192–201. 5. Beaulieu C. The basis of anisotropic water diffusion in the nervous system—a technical review. NMR Biomed 2002;15:435–55. 6. Song SK, Sun SW, Ju WK, et al. Diffusion tensor imaging detects and differentiates axon and myelin degeneration in mouse optic nerve after retinal ischemia. Neuroimage 2003;20:1714–22. 7. Sullivan EV, Rohlfing T, Pfefferbaum A. Quantitative fiber tracking of lateral and interhemispheric white matter systems in normal aging: relations to timed performance. Neurobiol Aging 2010;31:464–81. 8. Filippi CG, Bos A, Nickerson JP, et al. Magnetic resonance diffusion tensor imaging (MRDTI) of the optic nerve and optic radiations at

3T in children with neurofibromatosis type I (NF-1). Pediatr Radiol 2012;42:168–74. 9. Li J, Shi W, Li M, et al. Time-dependent diffusion tensor changes of optic nerve in patients with indirect traumatic optic neuropathy. Acta Radiol 2014;55:855–63. 10. Omodaka K, Murata T, Sato S, et al. Correlation of magnetic resonance imaging optic nerve parameters to optical coherence tomography and the visual field in glaucoma. Clin Experiment Ophthalmol 2014;42:360–8. 11. Scheel MH, Ambrose AL. Sugar ingestion and dichotic listening: increased perceptual capacity is more than motivation. Adv Cogn Psychol 2014;10:26–31. 12. Trip SA, Wheeler-Kingshott C, Jones SJ, et al. Optic nerve diffusion tensor imaging in optic neuritis. Neuroimage 2006;30:498–505. 13. Engelhorn T, Michelson G, Waerntges S, et al. Changes of radial diffusivity and fractional anisotropy in the optic nerve and optic radiation of glaucoma patients. Scientific World Journal 2012;2012:849632. 14. McLachlan SM, Prummel MF, Rapoport B. Cell-mediated or humoral immunity in Graves’ ophthalmopathy? Profiles of T-cell cytokines amplified by polymerase chain reaction from orbital tissue. J Clin Endocrinol Metab 1994;78:1070–4. 15. Nucci C, Mancino R, Martucci A, et al. 3-T Diffusion tensor imaging of the optic nerve in subjects with glaucoma: correlation with GDx-VCC, HRT-III and Stratus optical coherence tomography findings. Br J Ophthalmol 2012;96:976–80. 16. Anık I, Anık Y, Koç K, et al. Evaluation of early visual recovery in pituitary macroadenomas after endoscopic endonasal transsphenoidal surgery: quantitative assessment with diffusion tensor imaging (DTI). Acta Neurochir 2011;153:831–42 17. Naismith RT, Xu J, Tutlam NT, et al. Radial diffusivity in remote optic neuritis discriminates visual outcomes. Neurology 2010;74:1702–10. 18. Sun SW, Liang HF, Le TQ, et al. Differential sensitivity of in vivo and ex vivo diffusion tensor imaging to evolving optic nerve injury in mice with retinal ischemia. Neuroimage 2006;32:1195–204. 19. Schmierer K, Wheeler-Kingshott CA, Tozer DJ, et al. Quantitative magnetic resonance of postmortem multiple sclerosis brain before and after fixation. Magn Reson Med 2008;59:268–77. 20. Dolmann PJ. Evaluating Graves’ orbitopathy. Best Pract Res Clin Endocrinol Metab 2012;26:229–48. 21. Trobe JD. Optic nerve involvement in dysthyroidism. Ophthalmology 1981;88:488–92. 22. Kirsch E, von Arx G, Hammer B. Imaging in Graves’ orbitopathy. Orbit 2009;28:219–25.

© 2014 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc.

395

Copyright © 2014 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc. Unauthorized reproduction of this article is prohibited.

Quantitative Assessment of Optic Nerve With Diffusion Tensor Imaging in Patients With Thyroid Orbitopathy.

To detect abnormalities of the optic nerve in patients with thyroid orbitopathy using diffusion tensor MRI...
599KB Sizes 2 Downloads 15 Views