| Thyroid associated ophthalmopathy is an inflammatory autoimmune disease with complex etiology.Orbital changes in TAO result from de novo adipogenesis,hyaluronan synthesis,interstitial oedema and enlargement of extraocular muscles.Proptosis is one of the most common symptoms of TAO,coupled with a series of symptoms affecting the appearance,which including eye manifestations rangs from lid lag and retraction to eyelid swelling,conjunctival congestion and so on.The nature history of TAO comprises a dynamic phase that involved first the aggravescence of eye signs and then incomplete recovery,followed by a static phase.Immunosuppressive therapy is effective in active phase and less effective in static phase.Therefore,It is important to distinguish disease activity period which is responsive to immunosuppressive treatment.Quantitative measurement of the orbital soft tissue(orbital fat and extraocular muscles)in patients with TAO is helpful in understanding the pathogenesis and etiology of TAO.Purpose of the study:1.The study aimed to use the commercially available software(Mimics;Materialise,Louvain,Belgium)for the 3D reconstruction based on orbital MRI data,accurately calculating the orbital soft tissue volumes of patients with TAO patients and healthy people,and to validate the precision and feasibility of the method.2.We aimed to explore the clinical significance of orbital fat volume by measuring orbital fat volume coupled with activity indexes and the general clinical indicators.Materials and Methods:We quantitatively measured orbital fat volume(FV),and extraocular muscle volume(MV)on a manual phantom and 10 TAO patients.Two observers calculated phantom’ s volume which was constructed of skull,butter,and chicken muscle according to the previous studies.These calculations were compared with standard volume measured before.One of the observers measured a typical TAO case 10 times to calculate intraobserver variability.Three observers independently measured 10 TAO patients to calculate interobserver variability.Meanwhile,total of 35 patients with TAO in the outpatient clinic and inpatient department,department of endocrinology,the Third Affiliated Hospital of Southern Medical University from January,2016 to December,2016 were included in the study,with a total of 70 orbits.The correlation between orbital fat volume and the clinical indicators was evaluated.We also analysed the correlation between the SIR and the clinical indicators.The orbital fat volume between patients with TAO and 12 controls was compared.Results:1.Accuracy of the phantom calculations between the two observers varied from-4.60%to-2.78%for FV and between-4.13%and 0.71%for MV.Mean differences between the repeated calculations were smaller than 4%,except for the measurement of MV which is 5.84%.The intraclass correlation coefficient varied from 0.976 to 0.996.2.The orbital fat volumes were correlated with the TAO duration(r=0.521,P<0.01)and the proptosis(r=0.609,P<0.01).The course of disease which was more than one year would be the peak period of the increase in fat tissue.Increase of exophthalmos by 1 mm needed a orbital fat volume increment of 0.82ml.The orbital fat volume is an independent risk factor for disease severity.The CAS was correlated with the SIR(r=0.536,P<0.01)and the TRAb(r=0.416,P<0.01).The volume of the fat tissues in TAO group was significant higher than healthy individuals(P<0.01).Conclusion:1.Mimics(Materialise)is an valuable,high-efficiency tool for the 3D reconstruction of orbit soft tissues and the quantitative measurement of orbital soft tissue volume based on MRI thin slice scan(0.8mm).2.The course of disease which is more than one year may be the peak period of the increase in fat tissue.The orbital fat volume combined with the SIR can serve as an important basis to explore the best time for treatment.It also may be helpful to prognosis evaluation. |
