Diffusion-weighted MR imaging of thyroid nodules.

Introduction: The purpose of our study was to determine the diagnostic role of diffusion-weighted imaging (DWI) in the differentiating of malignant and benign thyroid nodules by using fine needle aspiration biopsy cytology criteria as a reference standard. The apparent diffusion coefficient (ADC) values of the normal-looking thyroid parenchyma were also evaluated both in normal patients and in patients with nodules.

Methods: Between March 2007 and February 2008, 76 consecutive patients with ultrasound-diagnosed thyroid nodules and 20 healthy subjects underwent diffusion-weighted MR imaging by using single-shot spin echo, echo planar imaging. A total of 93 nodules were included in the study using the following b factors 100, 200, and 300 mm(2)/s. ADC values of thyroid nodules and normal area in all subjects were calculated and compared using suitable statistical analysis.

Results: Mean ADC values for malignant and benign nodules were 0.96+/-0.65 x 10(-3) and 3.06+/-0.71 x 10(-3)mm(2)/s for b-100 factor, 0.56+/-0.43 x 10(-3) and 1.80+/-0.60 x 10(-3)mm(2)/s for b-200, and 0.30+/-0.20 x 10(-3) and 1.15+/-0.43 x 10(-3)mm(2)/s, for b-300, respectively. Mean ADC values of malignant nodules were lower than benign nodules. There were significant differences in ADC values between benign and malignant nodules. ADC values among normal-appearing thyroid parenchyma of patients and normal-appearing thyroid parenchyma of healthy subjects were insignificant at all b factors.

Conclusion: Benign nodules have higher ADC values than malignant ones. DWI may be helpful in differentiating malign and benign thyroid nodules.