## Materials and Methods
### Ultrasound Examination of Thyroid Gland  
GSU and SWE examinations of thyroid gland were performed on both sides of the neck of all patients. Due to the ethical issues and restricted policies of our institution, we had limited data access to the patient's clinical reports. Therefore, we could not check the stage of tumors of the patients. However, we had accessed to the histopathology and fine needle aspiration cytology results for the final diagnosis of the nodules. Cytopathology and/or histopathology diagnoses were used to correlate the accuracy of GSU and SWE findings. All of the thyroid ultrasound examinations were conducted by the same operator (M.Y.) using the same ultrasound unit in conjunction with a 4-15 MHz linear transducer (Aixplorer, Supersonic Imagine, Aix-en-Provence, France). All of the ultrasound examinations were performed with an imaging mechanical index (MI) of 1.5 and the MI of the \"push\" pulses for the SWE was 1.2. In the thyroid ultrasound examinations, we used a broadband frequency ultrasound transducer, which allows operators to choose different frequencies for examination. In the current study, we standardized the scanning protocol of using high frequency (~15 MHz) to optimize the image quality. During the ultrasound examination, patients were asked to lie in supine position on the examination couch with the neck and shoulders supported by pillow to keep patient's neck slightly hyperextended. A generous amount of coupling gel was applied and GSU was performed to identify any nodule in the thyroid lobes and isthmus. When a thyroid nodule was identified (based on perceived contrast between the echogenicity of thyroid nodule and adjacent thyroid parenchyma), multiple transverse, and longitudinal sonograms of the nodule were obtained. Each nodule was assessed for suspicious grey scale sonographic features [1; 21; 29; 30] including absent halo sign, microcalcification, hypoechogenicity, internal solid echotexture, tall to width ratio >1, and irregular margins (Figures 1 and 2). After GSU, SWE was then performed on the thyroid nodule. For patients with multiple thyroid nodules, SWE was performed on the largest thyroid nodule, and/or the nodule with one or more suspicious grey scale sonographic features, as described above. In the SWE examination, the size of the SWE acquisition box was first adjusted to cover the entire thyroid nodule. Multiple transverse and longitudinal shear wave elastograms of the nodule were obtained (Figures 3 and 4). Figure 3: Transverse elastogram (**upper**) and grey scale sonogram (**lower**) of a benign nodule in the right thyroid lobe of a 37-year-old patient. The value of elasticity indices (\(E_{\rm maximum}=32\) kPa and \(E_{\rm mean}=17.6\) kPa) were lower than the respective cut-off values reported in the present study. Figure 2: Longitudinal sonogram showing a papillary carcinoma in the left thyroid lobe of a 51-year-old patient (**arrows**). The nodule appeared hypoechoic, ill-defined, and had multiple microcalcifications (**arrowheads**). To acquire an elastogram, the transducer was held at the same position for at least 2 s to allow the SWE signal acquisition to settle and to reduce variability. During SWE examination, caution was made to avoid compression applying on the patient's neck by the transducer, which might affect the stiffness measurement of thyroid nodules. Taking shear wave elastograms in the scan planes showing calcification within the nodule were avoided. After the ultrasound examination, FNAC was performed on the targeted nodules. Nodules with confirmed malignancy (papillary carcinoma, follicular carcinoma, or medullary carcinoma) or indeterminate cytology (follicular neoplasm, follicular lesion of undetermined significance, atypia of undetermined significance, or repeated non-diagnostic cytology) were further evaluated by surgical resection and histopathological examination.