Comparative Study Of Gemstone Spectral CT And Conventional Ultrasound Spectroscopy For Differentiating Benign And Malignant Thyroid Nodules

Objective:To explore the value of the gemstone spectral CT imaging in differential diagnosis of benign and malignant thyroid nodules, and compare its diagnostic value with ultrasonography.Methods:Forty-four thyroid nodules, which were confirmed by biopsy, were included in this study, According to the pathology results, nodules were divided into benign group and malignant group. All patients’ thyroid and bilateral lymph nodes firstly accepted ultrasonography exams and energy spectrum CT scanning (including plain scanning and arterial phase enhanced CT scanning). The interval time of the ultrasound exam and the spectrum CT scan was not more than three days. .Firstly, we got the obtained spectrum CT images to be processed in the workstation (GE, aw44). Recorded the nodules’ and surrounding normal thyroid tissue’s iodine concentration and water content, and calculated standardized iodine concentration (water content), which was defined as nodules’ average iodine concentration (water content)/ipsilateral normal thyroid tissue’s average iodine concentration (water content). Then used 40 and 100 keV as a reference point to calculate spectral curve slope. The slope was defined as (HU40keV-HU100keV)/60. Observed the mono-energetic image and iodine based image of 70keV, then recorded and analyzed the number, border, cystic degeneration, calcification and the papillary structure of the inner of nodules respectively. Secondly, from the ultrasonic images of thyroid nodules, we recorded the nodular morphology, boundary, cystic degeneration, acoustic halo, ipsilateral lymph node medulla structure et al. Data of spectral CT imaging and ultrasonography were analyzed by independent sample t test or nonparametric test and multivariate Logistic regression analysis respectively. According to the two sets of data, receiver-operating characteristic (ROC) curve were drawn, and the optimal iodine concentration threshold to predict malignancy, sensitivity and specificity were obtained.Results:A total of 44 nodules were detected, including 23 benign and 21 malignant. By statistics analysis, in non-contrast CT imaging, the average iodine concentration, standardized iodine concentration, slope of spectral curve were 1.97 ×100ug/ml,0.49 and 0.23 for benign group;-l.42×100ug/ml,-0.20 and-0.20 for malignant group(P﹤0.05), and the difference has the statistic significance. In the arterial phase, no significant difference was found for each parameter between the two groups, and the average iodine concentration, standardized iodine concentration, slope of spectral curve of the two group were 16.61×100ug/ml,0.49 and 1.98 for benign group; 11.07×100ug/ml、0.35 and 1.30 for malignant group (P>0.05). The area under the receiver-operating characteristic(ROC) curve of iodine concentration, standard iodine concentration, energy spectrum curve slope in the diagnosis of malignant nodules were 0.92,0.86,0.90, and the best diagnostic threshold were 0.32×100μg/mL, 0.52,0.33. The optimal iodine concentration to predict malignancy was 0.32 ×100μg/mL in non-enhanced phase with 100％sensitivity and 79.5％ specificity. The border and cystic situation of thyroid nodules between the two groups have the statistic difference in ultrasonography with multivariate logistic regression analysis (P<0.05). The sensitivity, specificity and 95％ confidence interval was 84.2％,68.1％ and 0.71-0.90 respectively.Conclusion:Both gemstone spectral CT imaging in non-contrast phase and ultrasonography has potential value in diagnosis of benign and malignant thyroid nodules. The spectral CT can provide objective parameters. And the study shows that, for the nodules whose diameter great than or equal to 1 cm, the AUC by using iodine concentration, standard iodine concentration, energy spectrum curve slope of spectral CT in non-enhanced phase were higher than ultrasound, and the sensi-tivity and specificity of the optimal iodine concentration for the diagnosis of malignant thyroid nodules were also superior to ultrasound. The quantitative parameters of spectrum CT can help clinical doctors to decide if the patients with thyroid nodules should be accepted surgery or not, and avoid the unnecessary surgery in a certain extent.