Subjects
This study was approved by the ethics committee of Affiliated Hangzhou First People’s Hospital, Zhejiang University School of Medicine (No. 2018. 108-01) and written informed consent was obtained from all subjects. A total of 891 pathologically-confirmed cases of patients with 1086 thyroid nodules were recruited from January 2016 to October 2018. All patients were examined by preoperative ultrasonography and ultrasonic positioning. Patients with nodule diameter > 1.0 cm or < 0.3 cm, cystic dominated nodules and nodules with calcification that precluded the measurement of soft tissues, and thyroid nodules with complicating Hashimoto thyroiditis were excluded from the study[13-15]. Finally, this study involved 349 patients with 433 nodules, including 71 men and 292 women, with an average age of 48±11 years (range 23-78 years) (Figure 1).
Methods
Ultrasonic examination of thyroid lesions was performed using one of the following ultrasonic diagnostic scanners: MyLab 70 XVG (Genova, Italy), Esaote MyLab Classic C (Genova, Italy), Esaote Mylab 90 (Genova, Italy), GE Voluson E8 (Tiefenbach15, Austria), GE Voluson E10 (Tiefenbach15, Austria), GE logic E9 (Wauwatosa, USA), Philips HD 11 XE (Amsterdam, Netherlands), Philips HDI 5000 (Amsterdam, Netherlands), Siemens S2000 (Buffalo Grove, USA), Mindray Resona7 (Shenzhen, China), and so on. Then, 5-13 MHz broadband linear array probes were used for this study, and the central frequency was 7.5 MHz. Patients were placed in a supine position, exposing the anterior cervical region, after which transverse, longitudinal, and oblique scans were performed.
Ultrasonic examination
The ultrasonographic data, selected from the Picture Archiving and Communication Systems database, were analyzed by two radiologists with 14 and 16 years of experience, respectively. The ultrasound grayscale values of the PTMC, micronodular goiters and thyroid tissues at the same gain level were retrospectively reviewed using the RADinfo radiograph reading system (Yilaida, Zhejiang Province), and the corresponding UGSR values were calculated. UGSR was the specific value between the grayscale of PTMC or micronodular goiters and the normal thyroid tissue at the same level. Afterward, patients were divided into the outpatient examination, preoperative positioning, and mean value groups. Outpatient examination group included patients who underwent thyroid ultrasound examination, preoperative positioning group included these outpatients to receive ultrasound again before thyroidectomy, the mean value group included the mean UGSR of the two groups above. The optimal UGSR value for differentiating PTMC from micronodular goiters was determined by analyzing receiver operating characteristic (ROC) curves. The calcification and necrosis regions were avoided during the region of interest (ROI) measurements. For nodules with homogeneous echo, an ROI > 1/2 of the largest areas of nodules was selected; for nodules with heterogeneous echo, an ROI > 1/2 of echo-dominated areas within regions was selected; and for measuring the grayscales of surrounding normal thyroids, ROIs of nodules at the same gain level and size were selected (Figure 2-4).
Statistical analysis
The SPSS for Windows version 17.0 software package (IBM Corporation, Armonk, NY) was used to generate the ROC curves for differentiating PTMC from micronodular goiters. The UGSR threshold was determined by measuring the area under the ROC curve. Differences in the UGSR value between and within groups were compared using either the analysis of variance or Student’s t-test. Reliability analysis of the UGSR was performed in the outpatient examination and preoperative positioning groups. P-values less than 0.05 were considered to be statistically significant.