The Value Of MR Diffusion-weighted Imaging In The Differential Diagnosis Of Thyroid Nodules

Objective: To investigate the value of MR diffusion weighted imaging(DWI) in differentiating malignant from benign thyroid leisions.Materials and methods: 60 patients with thyroid leisions, including86 thyroid nodules, underwent MRI routine examination and DWI examination before surgery. The diagnoses of thyroid leisions were confirmed by pathological results. The characteristics of the MR imaging of thyroid benign and malignant nodules were analyzed retrospectively.ADC values of benign nodules, malignant nodules and normal thyroid tissue, with different b values(b values were 300, 400 and500s/mm2), were analyzed and ROC curve was made to analyze the diagnostic efficiency of the ADC values. rADC values of benign nodules and malignant nodules, with different b values, were analyzed and ROC curve was made to analyze the diagnostic efficiency of the rADC values.The ADC and rADC values of thyroid nodules, with different b values,were compared with percentage of Ki-67 proliferation index. All the sample tests were considered P<0.05 as statistically significant.Results: According to histological results, there was 61 benign leisions and 25 malignant leisions in 86 thyroid nodules. The MRI findings of malignant leisions were unregular shape, incomplete borders,less cyst and transversal-longitudinal axes ratio over one, which were rare in benign leisions. With the increase of b value, ADC values of the same type reduced. The mean ADC values of malignant nodules were lower than that of benign nodules and normal tissues with the same b value.When b=500s/mm2, selecting 1.600×10-3mm2/s as ADC threshold for the diagnosis of malignant and benign thyroid nodules, the sensitivity was85.2% and specificity was 80.0%, which was the best diagnostic performance. When b=500s/mm2, selecting 0.940 as rADC threshold for the diagnosis of malignant and benign thyroid nodules, the sensitivity was72.7% and specificity was 98.0%, which was the best diagnostic performance. With all b values, ADC values and rADC values of benign and malignant thyroid nodules were not related with Ki-67 proliferation index.Conclusion: Uncomplete boundary and discontinuous peritumoral pseudocapsule were characteristic features of malignant nodules. rADC values were more effectable than ADC values in differentiating benign and malignant thyroid nodules.