Diffusion-Weighed MR of the Thyroid Gland in Graves' Disease: Assessment of Disease Activity and Prediction of Outcome

Rationale and Objectives: To assess the activity and clinical course of Graves' disease with diffusion-weighted magnetic resonance (MR) imaging. Materials and Methods: Fifty-one patients with Graves' disease and 25 volunteers underwent diffusion MR imaging of the thyroid gland using a single shot echo-planar imaging with b-factor of 0, 300 and 600 second/mm(2). The apparent diffusion coefficient (ADC) values of the thyroid gland were calculated. Patients with active Graves' disease included untreated patients at initial diagnosis (n = 12), patients under antithyroid drugs (n = 11), and patients in relapse after withdrawal of therapy (n = 13). Patients with inactive disease had a remission of hyperthyroidism (n = 15). Results: The mean ADC values of thyroid gland with active Graves' disease was 0.65 +/- 0.03 x 10(-3) mm(2)/second in patients at initial diagnosis, 0.81 +/- 0.02 x 10(-3) mm(2)/second in patients undergoing antithyroid drug and 0.72 +/- 0.07 x 10(-3) mm(2)/second in patients with relapse of hyperthyroidism. The mean ADC of patients with remission was 0.94 +/- 0.03 x 10(-3) mm(2)/second and for normal volunteer was 1.06 0.08 x 10(-3) mm(2)/second. There was significant difference in the ADC value of patients with active disease and remission (P = .001). The cutoff ADC value used for differentiating patients with active disease from patients with remission was 0.82 x 10(-3) mm(2)/second. The mean ADC value of thyroid gland had positive correlation with thyroid-stimulating hormone (r = 0.87, P = .001) and negative correlation with serum T4 (r = 0.82, P = .001) and serum T3 (r = 0.71, P = .001). Conclusions: The ADC value of the thyroid gland is a promising non invasive parameter for diagnosis of different clinical stages of Graves' disease. Hence it can be used to assess the activity and predict the outcome of patients during and after medical treatment.