ABSTRACT
<p><b>OBJECTIVE</b>To analyze the relationship between orbital fat volume and the progression and prognosis of thyroid- associated ophthalmopathy (TAO) and determine the optimal treatment timing for TAO.</p><p><b>METHODS</b>The clinical data were collected from 35 patients (70 orbits) with a definite diagnosis of TAO between January, 2016 and December, 2016. The correlation between orbital fat volume and the clinical parameters was evaluated. We also analyzed the correlation of the signal intensity ratio (SIR) of the extraocular muscles with the clinical parameters. The orbital fat volume was compared between patients with TAO and 12 control subjects.</p><p><b>RESULTS</b>The orbital fat volume was significantly correlated with the duration of TAO (r=0.480, P<0.01), but showed no significant difference between patients with a disease course within 6 months and those with a disease course of 6 to 12 months (P=0.084). The patients with a disease course beyond 12 months had a significantly greater orbital fat volume than those with a disease course of 6 months (P<0.01) or 6 to 12 months (P<0.05). The orbital fat volume was correlated with the degree of proptosis (r=0.622, P<0.01), and an increase of exophthalmos by 1 mm was associated with a total orbital volume increment of 0.88 mL. The clinical activity score was correlated with the SIR of the extraorbital muscles (r=0.536, P<0.01) and levels of anti-thyroid-stimulating hormone receptor antibody (r=0.416,P<0.01). The orbital fat volume was significantly greater in TAO patients than in the healthy individuals (P<0.01).</p><p><b>CONCLUSION</b>In patients with TAO, the peak increase of orbital fat volume occurs one year after the disease onset. Measurement of the orbital fat volume combined with SIR of the extraorbital muscles can serve as an indicator for determining the optimal timing for intervention of TAO and helps in the evaluation of prognosis of the patients.</p>
ABSTRACT
<p><b>OBJECTIVE</b>To establish a new method for rapid and quantitative measurement of orbital fat volume based on magnetic resonance imaging (MRI) data.</p><p><b>METHODS</b>We collected MRI data from normalized mold and patients with the diagnosis of thyroid-associated ophthalmopathy (TAO). The cross-sectional areas of the orbital fat on each MR image slice were measured to calculate the fat volume on each slice and then the total orbital fat volume. We recorded the time for completing the measurement and assessed the precision, reliability, repeatability and interoperator variations of the results.</p><p><b>RESULTS</b>This MRI data-based method allowed precise measurement of the orbital fat volumes with an absolute value of the mean percentage difference <1%. This method was fast and the results showed a good repeatability (with CVs <1%), a high reliability (ICC=0.996, 95%CI: 0.985-0.999) and a high interoperator concordance (95%CI of the Bland-Altman: -0.54-0.90).</p><p><b>CONCLUSION</b>The novel method we established for orbital fat volume measurement is rapid, accurate, reliable and reproducible with a low learning cost for clinical use.</p>