## 4 Discussion  
Differential diagnosis of thyroid nodules to predict malignancy poses a diagnostic dilemma in clinical settings. FNAC and histopathology examination of surgical specimen of thyroid nodules are the standard procedures to diagnose thyroid cancer. FNAC has a false-positive rate of 1-11.5% and a false-negative rate about 7.7%, whilst 20-30% of cases are non-diagnostic [31; 32]. However, the technique is highly dependent on the experience of the pathologists and the adequacy of the samples attained. Moreover, histopathological features of malignant thyroid nodules overlap with benign nodules, and thus there is a high incidence of \"skip diagnosis\". GSU is commonly used to assess thyroid nodules but no single GSU feature can accurately predict thyroid malignancy [33]. SWE is a novel ultrasound technique that measures tissue elasticity by tracking shear wave propagation through body tissues and provides quantitative measurements. The technique is less operator-dependent and highly reproducible [10]. SWE evaluation of thyroid nodules has been documented. However, the reported cut-off levels to differentiate benign and malignant nodules were variable, which was probably due to different methodologies used in the studies. Among the available literature, the highest cut-off values of SWE indices for evaluating thyroid malignancy were \(\geq\)95 kPa for \(E_{\text{maximum}}\), \(\geq\)85.2 kPa for \(E_{\text{mean}}\) and \(\geq\)54.2 kPa for \(E_{\text{minimum}}\)[34]. However, [PERSON] et al. [35] found that E\({}_{\text{mean}}\) of 34.5 kPa or higher was a significant predictor of malignancy with a sensitivity of 52.9% and specificity of 77.8%. Other studies suggested that SWE was useful in differentiating benign and malignant thyroid nodules when the cut-off level of 66 kPa and 65 kPa for \(E_{\text{maximum}}\) were used, respectively [15; 36]. However,  
Figure 6: Receiver operating characteristic (ROC) curves showing comparison between grey scale ultrasound features alone (usg. combine) and in combination with \(E_{\text{maximum}}\) (usg. \(E_{\text{max}}\)) and \(E_{\text{mean}}\) (usg. \(E_{\text{mean}}\)) in distinguishing benign and malignant thyroid nodules. Area under the curve, AUC, of usg. combine, usg. \(E_{\text{mean}}\), and usg. \(E_{\text{maximum}}\) were 0.714, 0.775 and 0.769 respectively. [PERSON] et al. [37] found that the threshold value of 50 kPa for \(E_{\text{maximum}}\) was the most useful SWE parameter in the differentiation of benign and malignant nodules. Using the cut-off value of \(\geq\)53.2 kPa for \(E_{\text{maximum}}\geq\) 34.5 kPa for \(E_{\text{mean}}\) and \(\geq\)21.8 kPa for \(E_{\text{minimum}}\), [PERSON] et al. [33], found that SWE was superior to conventional GSU in identifying malignant nodules. Among different SWE indices, they found that \(E_{\text{mean}}\) yielded the highest diagnostic accuracy (79.6%). [PERSON] et al. [13] also reported that \(E_{\text{mean}}\geq\) 38.3 kPa was the most useful predictor among all SWE indices in differentiating benign and malignant thyroid nodule. In the present study, the optimal cut-off for \(E_{\text{maximum}}\) and \(E_{\text{mean}}\) for distinguishing benign and malignant nodules were 67.3 and 23.1 kPa, respectively, which were consistent with the result of previous reports in \(E_{\text{maximum}}\)[15; 36]. In our study, there was no significant difference in the \(E_{\text{minimum}}\) of benign and malignant nodules, which was different from previous studies [13; 33; 34]. The difference was due to the different methodologies used in the present and previous studies. Previous studies used ROI (Q-box(tm)) with fixed size and placed it over the stiffer region of the nodule for the stiffness measurement. It involved subjective judgement of the operator in the placement of the ROI. However, the present study adjusted the size of the ROI so that it covered the entire nodule. The process did not involve operator's judgement in which the ROI should be placed, and thus it was more objective.