Value Of Diffusion Weighted Imaging In Diagnosis Of Nodular Lesions Of Thyroid: A Preliminary Study

ObjectiveMagnetic resonance diffusion weighted imaging is the only technique which can detect the molecular diffusion of water in vivo. The present study is to (1) choose the most optimum b value for detecting nodular lesions of thyroid, (2) determine whether the ADC value had significant discrepencies between benign and malignant nodulars, (3) analyze the manifestations of conventional MRI and DWI as to determine the value of DWI in differentiation of thyroid nodulars. Materials and methodSixty cases of nodular lesions of thyroid were divided into two groups as benign and malignant. The malignant group included twenty-two papillary carcinomas, two undifferentiated carcinomas, one medullary carcinoma and five lymphomas. The benign group included eleven adenomas and niniteen nodular goiters. All cases were proved histopathologically and proceeded conventional MRI (including axial T₁WI, T₂WI and fat-suppressed T2WI) and DWI. The raw data of DWI were processed offline on the workstation to form the corresponding maps of ADC. With accordance to T₁/T₂WI, the ADC values of ROI in the solid part of nodular lesions with different b values was measured. The ADC values with different b values of each group were proved to be a Gaussian distribution and independent samples t-test were performed with software SSPS 11.0. And the ADC values with different b values of malignant group performed ANOVA for statistical analysis. A p value less than 0.05 was considered significant difference. The best diagnostic threshold of ADC value formalignant nodulars was choosed on the basis of ROC curve, and this threshold was used to analyze the diagnostic sensitivity and specificity for malignant thyroid nodulars. Result:1. Conventional MRIMalignant nodulars of thyroid usually had irregular and lobulated shape, and the margin of the lesions was ill defined and could not be depicted from the neiboring normal thyroid clearly. There were six cases of which the trachea and/or cervical vessels were involved. And in twenty-one cases enlarged lymph nodes in the neck could be found. The lesions often showed slightly hypo/hyper/isointense on TiWI, and hyperintense signal on T2WI. The signal intensity of the lesions was inhomogeneous, and cystic degeneration and necrosis or hemorrhagic areas could be demonstrated of which showed long-Ti and long-T2 signal intensity or short-Ti and long-Tz signal intensity respectively. The enlarged lymph nodes showed hyperintense signal on T2WI.Benign nodulars of thyroid usually had regular shape, and the margin of the lesions were well defined and could be depicted from normal thyroid clearly. In ten cases, slightly enlarged lymph nodes in the neck could be found. In the cases of nodular goiter, there were multiple nodulars, and thyroid was diffused enlarged with different degree. The lesions often showed slightly hypo/isointense signal on TiWI, and hyperintense signal on T2WI. The signal intensity of the lesions was inhomogeneous, and cystic degeneration and necrosis or hemorrhagic areas could be found of which showed long-Ti and long-T2 signal intensity or short-Tl and long-T2 signal intensity respectively. The enlarged lymph nodes showed hyperintense signal onT2WI.2. DWITwenty-two cases of papillary carcinoma showed slightly hyperintense signalon DWI and slightly hypointense signal on corresponding ADC maps, their signal intensity was inhomogeneous. Five cases of thyroid lymphoma showed obviously hyperintense signal on DWI and obviously hypointense signal on corresponding ADC maps, their signal intensity was homogeneous. Two cases of undifferentiated carcinoma showed obviously hyperintense signal on DWI and obviously hypointense signal on corresponding ADC maps, their signal intensity was homogeneous. One case of medullary carcinoma showed slightly hyperintense signal on DWI and slightly hypointense signal on corresponding ADC maps, its signal intensity was not very homogeneous. Nineteen cases of nodular goiter showed slightly hyperintense signal on DWI and slightly hyperintense signal on corresponding ADC maps, their signal intensity was inhomogeneous. Eleven cases of adenoma showed slightly hyperintense signal on DWI and slightly hyperintense signal on corresponding ADC maps, their signal intensity was homogeneous.The ADC values with different b values of benign group had statistical difference, with b value increasing, the ADC value decreased. The ADC values with different b values of malignant group had significant difference, with b value increasing, the ADC value decreased. The ADC value of the two groups with the same b value had statistical difference, and the ADC value of malignant group was significant lower than that of benign group. Conclusion:1. With b value of DWI for nodular lesion of thyroid increasing, the ADC value would decreased. And for this kind of machine, the most optimum b value of DWI for differentiate thyroid nodulars was 400s/mm².2. DWI provided fuctional informations which the conventional MRI could not do. The ADC value had significant difference between benign and malignant group. The analysis of DWI and the measurement of ADC value could be used to differentiate benign and malignant lesions which would complement the deficit of conventionalMRI.3. If we set the ADC ^ 1.475 X 10'3 mm2/s as the threshold, the diagnosticsensitivity and specificity for malignant nodulars of thyroid was 93.3% and 96.7%respectively.Original Points:This present study analysed the value of DWI in diaffrentiating of nodular lesions of thyroid, and set the most suitable b value for thyroid lesions. The study also proved that the ADC value had significant difference between benign and malignant lesions. And the ADC threshold which used for differentiating benign and malignant lesions was determined, it gave us much more information for diagnosis.