Objective:(1) To evaluate the diagnostic value of CT morphology on the differential diagnosis between benign and malignant thyroid nodule (2) To evaluate the diagnostic value of iodine concentration on the differential diagnosis between benign and malignant thyroid nodule. (3) To evaluate the diagnostic value of DE spectral curve on the differential diagnosis between benign and malignant thyroid nodule.Methods:Among total of 108 cases of thyroid nodule found between year 2013 to 2015 from first affiliated hospital of Kunming medical university, included 72 malignant and 36 benign cases。 All the patients included for study of thyroid nodule either benign or malignant underwent DE-CT plain scan of the thyroid region in the neck. All nodules were confirmed by pathology, and with the diameter greater than 0.5 cm. On conventional CT images, analyzing the nodular morphology, including size, edge, margin, capsule and calcification.The nodules with undefined margin, irregular edge, incomplete capsule and small calcification were being diagnosed as malignant, and vice versa as benign nodules. Measuring iodine concentration on DECT iodine maps and obtaining monoenergetic curve to calculate spectrum curve slope. Comparing with the pathological result, analyzing the accuracy of morphology, iodine concentration and energy spectral curve in the identification of benign and malignant nodules. Evaluating the diagnosis efficiency of maximum iodine concentration and spectral curve by ROC analysis.Results:In total of 108 cases found during our retrospective cases analysis, included 72 thyroid nodules were malignant and 36 were benign cases of which 65 females and 43 males were found. The mean age was around 48 years or more.Morphology:(1)Diameter (Edge and capsule):The thyroid nodules which showed irregular and incomplete surface diameter with edge and capsule indicating malignant nodule and with complete and regular edge, capsule as benign nodule. Out of 72 malignant thyroid nodules, which were confirmed by pathology,48 were found with irregular, incomplete edge and capsule, the sensitivity was 66.67%. Out of 36 benign thyroid nodules, which were confirmed by pathology,18 were found with regular, complete edge and capsule, the specificity was 50.00%. And accuracy was found to be 61.11%.(2)Calcification:We considered two aspects whether the calcification was present or absent and the calcification was small (<2.0cm) or big (>2.0cm). The thyroid nodules, which had calcification, were considered as malignant and without calcification as benign. Out of 62 thyroid nodules, which had calcification,48 were malignant and 12 were benign respectively. Out of 46 thyroid nodules without calcification,22 were found to be malignant and 24 benign. The sensitivity, specificity and accuracy were found to be 66.67%,61.11% and 64.81% respectively. The thyroid nodules that had small calcification (<2.0cm) were considered as malignant and big calcification (>2.0cm) as benign. Out of 49 thyroid nodules, which had small calcification,42 were found to be malignant, and 7 as benign nodules. Out of 59 thyroid nodules having big calcification,30 were found to be malignant and 29 as benign conditions. The sensitivity, specificity and accuracy were found to be 58.33%,80.56%,65.74% respectively.(3)Combined edge, capsule and small calcification:CT imaging in MPR in any level of observation, if thyroid nodules is incomplete, irregular, or had small calcification, we considered it malignant, if the thyroid nodule is complete and regular, or without calcification, or have large calcification, considering it benign respectively. The sensitivity, specificity and accuracy were found to be (Table 1):(50/72) 69.44%, (31/36) 86.11%, (81/108) 75.00% respectively.2. Iodine concentration or value:The CT attenuation value and iodine concentration range of malignant nodules was 22.9～52. 1HU(average 30.2±0.5HU) and -3.2～1.0mg/ml (median～1.5mg/ml). The CT attenuation value and iodine concentration range of benign nodules was 30.2～55.1HU(average 39.4±0.7HU) and -0.5～1.8mg/ml (median 0.9mg/ml). The CT attenuation value and iodine concentration range of normal thyroid tissue of malignant nodules was 47.4-85.6HU(average 66.8±1.3HU) and 1.1～3.2mg/ml (averagel.8±0.1mg/ml). The CT attenuation value and iodine concentration range of normal thyroid tissue of benign nodules was 56.8～85.7HU(average 68.4±1.8HU) and 1.2-3.0mg/ml (average 1.7±0.1mg/ml). There was correlation between the CT attenuation value and iodine concentration range of those groups (r=0.755,0.678,0.813,0.774,p=0.000). Among them, the CT attenuation value and iodine concentration of benign nodules solid part was significantly higher than malignant nodules; the difference was statistically significant (Z=-4.650,p=0.001,0.000). While the CT attenuation value and iodine concentration of normal thyroid tissue between malignant nodules and benign nodules was accordance, there was no statistically significant difference (T=3.753, 0.932,p=0.225,0.112). When critical value was 0.15mg/ml, sensitivity was 81.50%, specificity was 80.00%.3. Spectrum curve slope (SCP):1.The spectral curve value of malignant thyroid nodules range was 0.16-0.76 HU (median-0.33mg/ml). The spectral curve slope of benign nodules range was 0.53-1.13HU (median 0.78mg/ml). The spectral curve slope range of normal thyroid tissue was 0.81-1.91HU (median 1.39mg/ml).2. Using Wilcoxon test, there was a correlation between malignant, benign and normal thyroid nodules. The spectral curve slope value of malignant and benign thyroid nodules was (Z=3.072,P=0.002), Malignant and normal thyroid nodules was (Z=3.107,P=0.002), benign and normal thyroid nodules was (Z=3.055,P=0.002). The differences between the groups were statistically significant (P all<0.05). SCP Sort:malignant nodules <benign nodules <normal thyroid.3. Using ROC curve, the correlation between CT median value and tube voltage energy of normal, benign and malignant nodules, the visible spectral curve slope had some differences. The malignant nodules slope indicated as red color was downward descending on the lower side below the benign slope. Whereas the benign spectral curve slope was in between normal and malignant, while normal thyroid spectral curve slope was descending downward above benign slope. So finally the threshold SPSS software ROC curve selected the best sensitivity and specificity of SCP, the area under the curve AUC value of 0.906, indicating its high diagnostic accuracy. The sensitivity and specificity and maximum accuracy for the best critical point, the critical value of 0.51, the sensitivity was 81.00% and a specificity of 81.00% respectively.Conclusion:1. CT routine plain imaging, the accuracy of diagnosis thyroid nodules have values, but couldn’t satisfy the needs in clinical. 2. Iodinevalue, and SCP could diagnosis of malignant and benign thyroid nodules more accurately than traditional CT plain imaging.