Investigation On The Value Of Spectral CT In Differential Diagnosis Of Thyroid Benign And Malignant Nodules

Backgrounds and Objective: Thyroid nodule is the most common thyroid disease.Clinically, nodular goiters, thyroid adenoma and carcinoma are the most common. Thequalitative diagnosis of the thyroid nodule is very important to the way of treatment,and early diagnosis of thyroid carcinoma is also of great significance to early treatmentand patient prognosis. Fine needle aspiration cytology (FNAC) is the most accuratemethod for qualitative diagnosis of thyroid nodule. Due to the invasiveness andpossibility of implantation metastasis. Clinically, the differential diagnosis of thyroidnodule usually depends on imaging examination. Ultrasound, CT, MRI and radionuclideimaging can be used for thyroid disease. Due to the convenience, no radiation and highaccuracy, Ultrasound is the preferred method. MRI imaging is better for showingnodule boundary and invasion to the surrounding tissue. But it is not sensitive tocalcification, and with long scan time and more artifacts. Radionuclide imaging is usedfor detecting systemic metastasis and postoperative recurrenced lesion of thyroidcarcinoma, not generally used for diagnosing thyroid carcinoma. With higher densityresolusion, CT can clearly show the calcification, cystic change, infiltration, and lymphnode metastasis. But for the diagnosis of benign and malignant nodules, the specificityof CT is not very high. As a new CT technique, spectral CT can achieve themonoenergetic imaging with the core technology of fast switch between80and120kVp. With the function of material separation, it can quantitatively analyse the contentof basic material. The most used basic material pair is iodine-water pair, which issensitive to the change of iodine, especially. By the function of quantitative iodineanalysis, we explore the value of gemstone spectral CT in differentiating thyroidnodules. Patients and Methods: A total of103patients with thyroid nodules were enrolled inthe retrospective study. All the patients underwent spectral imaging CT scan, and30ofthem underwent dual-phase enhanced scan.23men, age45.4±14.3years;80women,age51.3±12.7years. All the work was completed on the GSI viewer of the GE AW4.4workstation. The monoenergetic image, iodine-based image and water-based imagewere obtained. For the noncontrast image, the arterial phase (AP) and venous phase (VP)images, ROI was defined to get the iodine concentration (IC) on the monoenergeticimage at70keV. Normalized IC (NIC) of AP and VP was calculated. Besides,conventional morphology characteristics such as the margin, cystic change, calcificationand edge interruption sign were reviewed and recorded. Nodules were divided into thebenign and malignant group, based on the pathological results. IC and NIC werecompared between benign and malignant nodules by a two-sided Wilcoxon rank sumtest. P value <0.05was considered statistically significant. The optimal threshold topredict malignancy was obtained by receiver operating characteristic curve (ROC). ICand the conventional morphology characteristics were analysed by univariate regressionanalysis. Independent variable with a P value <0.25was considered valuable andincluded in the multivariate logistic regression analysis. Multivariate ROC analysis wasperformed to evaluate the efficacy of combining the IC and conventional morphologycharacteristics.Results: In total,119nodules (87benign and32malignant) were detected. IC innoncontrast phase: benign group:1.84(-0.10,4.72)(mg/ml); malignant group:-0.05(-1.44,1.06)(mg/ml). NICAP: benign group:0.22(0.10,0.33); malignant group:0.21(0.06,0.36). NICVP: benign group:0.51(0.39,0.68); malignant group:0.27(0.19,0.40). The IC and NICVPof malignant nodules were significantly lower than benignnodules in the noncontrast and venous phase (Z=-3.534, Z=-3.831, P=0.000). Theoptimal IC and NICVPthreshold was0.68mg/ml and0.38, achieving74.3%and76.9% sensitivity,66.7%and80.0%specificity, respectively. For the multivariate analysis, thearea under the ROC was0.87in noncontrast phase. Sensitivity of77.1%and specificityof84.5%were achieved.Conclusion: Gemstone spectral CT can generally evaluate the abnormal iodine contentseen in thyroid nodules, with certain value in differential diagnosing benign andmalignant nodules. However, there are some overlaps in the iodine concentration ofbenign and malignant nodules. A comprehensive analysis combining spectrumparameter and morphology characteristics has higher efficiency in differentialdiagnosis.