Background: Nodules are the most frequent lesion in thyroid gland. They are discovered clinically on self-examination by the patient, during a clinical examination or accidentally during a radiologic procedure; with applying different imaging modalities in recent years, thyroid nodules are being more frequently accidentally discovered.

Aim of the work: Establishing the precision of Diffusion-Weighted Imaging (DWI) and Apparent Diffusion Coefficient (ADC) values in diagnosing benign and malignant nodules, considering histopathology as the highest diagnostic modality.

Materials and Methods: Diffusion was measured both intuitively and quantitatively using trace images and the apparent diffusion coefficient (ADC) parameter. On the trace image, malignant tissues with restricted diffusion were bright, and on the ADC map, they were hypo-intense, with much lower ADC values than benign thyroid nodules.

Results: All of the patients had their thyroid nodules histopathologically examined, and the results revealed that there were 26 benign nodules (76.5%) and 8 malignant nodules (23.5%), respectively. The results of histopathological examinations were compared to DWI and ADC values derived by magnetic resonance imaging (MRI). All subjects underwent DW-MRI with a b value of 600 s/ mm2. Thyroid nodule mean ADC values were determined.

Conclusion: Quantitative DWI could be a reliable imaging method for thyroid nodule detection because it is found to have high specificity and sensitivity. The ADC values seem to be able to discriminate benign from malignant thyroid lesions.