Role of apparent diffusion coefficient values in differentiation between malignant and benign solitary thyroid nodules.

BACKGROUND AND PURPOSE Accurate imaging characterization of a solitary thyroid nodule has been clearly problematic. The purpose of this study was to evaluate the role of the apparent diffusion coefficient (ADC) values in the differentiation between malignant and benign solitary thyroid nodules. MATERIALS AND METHODS A prospective study was conducted in 67 consecutive patients with solitary thyroid nodules who underwent diffusion MR imaging of the thyroid gland. Diffusion-weighted MR images were acquired with b factors of 0, 250, and 500 s/mm(2) by using single-shot echo-planar imaging. ADC maps were reconstructed. The ADC values of the solitary thyroid nodules were calculated and correlated with the results of histopathologic examination. Statistical analysis was performed. RESULTS The mean ADC value of malignant solitary thyroid nodules was 0.73 +/- 0.19 x 10(-3) mm(2)/s and of benign nodules was 1.8 +/- 0.27 x 10(-3) mm(2)/s. The mean ADC values of malignant nodules were significantly lower than those of benign ones (P = .0001). There were no significant differences between the mean ADC values of various malignant thyroid nodules, but there were significant differences between the subtypes of benign thyroid nodules (P = .0001). An ADC value of 0.98 x 10(-3) mm(2)/s was proved as a cutoff value differentiating between benign and malignant nodules, with 97.5%, 91.7%, and 98.9% sensitivity, specificity, and accuracy, respectively. CONCLUSION The ADC value is a new promising noninvasive imaging approach used for differentiating malignant from benign solitary thyroid nodules.