[Application of nuclear magnetic dispersion weighted imaging and apparent diffusion coefficient in the identification...

Objective:To determine the diagnostic role of diffusionweighted imaging(DWI) and apparent diffusion coefficient（ADC） under different b values in differentiating benign and malignant thyroid nodules by using postoperative histopathological results were taken as the reference standard. Method: From January 2017 to June 2018, 64 patients with thyroid nodules diagnosed by ultrasound in the head and neck surgery of Shanxi Cancer Hospital were collected, and a total of 80 nodules were collected. The Philips 3.0T superconducting magnetic resonance imaging system was used for T1 weighting, T2 weighting, and DWI horizontal axis scanning imaging. The b values were 300, 500, 800 and 1 000 s/mm², respectively. Taking postoperative histopathological results as the reference standard, the ADC values of thyroid nodules of all subjects were calculated and compared, and the working characteristics(ROC) curves of all subjects with b values were drawn, the area under the curve was calculated, and the threshold value of differentiating benign and malignant thyroid nodules was obtained. Result:A total of 80 nodules, 33 malignant and 43 benign were excluded, including 1 diffuse b-cell non-hodgkin's lymphoma, 2 parathyroid cysts, and 1 pure cystic patient. A total of 76 nodules were included. When b values were 300, 500, 800 and 1 000 s/mm², the average ADC values of malignant nodules were(1.498±0.210) ×10⁻³mm²/s, (1.311±0.190) ×10⁻³mm²/s, (1.134±0.170) ×10⁻³mm²/s, (0.972±0150) ×10⁻³mm²/s. The mean ADC values of benign nodules were(2.207±0.390) ×10⁻³mm²/s, (1.928±0.430) ×10⁻³mm²/s, (1.702±0.410) ×10⁻³mm²/s,(1.557±0.420) ×10⁻³mm²/s. At the same b value, the average ADC value of malignant nodules was lower than that of benign nodules, and the difference was statistically significant(t values were 9.279,7.641,7.301,7.569, P values were 0.000,0.000,0.000,0.000,0.000). The average ADC values of the benign and malignant nodules decreased with the increase of b value, and the difference was statistically significant(the F values of the benign and malignant groups were 210.091 and 353.822, respectively，P values are 0.000, 0.000). Under different b values, the area(AUC) of ROC curve is 0.927,0.884,0.878,0.901,and 95%CI are 0.862-0.993,0.804-0.956,0.794-0.962 and 0.829-0.972, respectively. When b value is 300 s/mm², AUC is the largest, indicating that it is the best indicator to distinguish benign and malignant thyroid nodules. The diagnostic threshold of benign and malignant nodules is 1.802×10⁻³mm²/s. Specificity, sensitivity, accuracy, positive predictive value, and negative predictive value were 95.00%,86.11%,90.79%,93.94% and 88.37%, respectively. Conclusion: DWI is a noninvasive diagnostic tool used to identify benign and malignant thyroid nodules. It can help to make a definite diagnosis before surgery and reduce the unnecessary burden of surgery.