## 4 Discussion  
SE has been extensively studied in the evaluation of thyroid nodules with excellent results [21, 38]. Initially, its role in replacing grayscale US was discussed, given its high diagnostic quality, but studies rapidly established its role, rather, as an additional beneficial tool, given that conventional US needs to remain the basis of evaluation [39]. The more recently developed shear-wave imaging techniques recorded over the years promising results in the assessment of the stiffness of the liver [40, 41], kidney [42], spleen [43], and breast lesions [44, 45], but also for the evaluation of thyroid nodules [22, 24]. The techniques are constantly developing, with slightly different results varying based on the equipment and the methods that were used. Most of the literature data provide a comparison between SE and SWE in different populations. This study intended to evaluate the diagnostic potential of the two methods and detect any significant differences between the two types of evaluation by providing a consecutive evaluation of both methods in the same population. One meta-analysis that aimed to compare the SE and SWE evaluations, including 80 trials with a total of 16,624 subjects, revealed superior diagnostic quality for SE compared to SWE in differentiating malignant and benign thyroid nodules [46], but it did not include any comparison of the methods in the same group. An important side note is the substantial share of SE studies that were included compared to the number of studies on SWE, and the lack of uniformity in the US evaluation and SWE techniques. The meta-analysis did conclude that the techniques hold a similar diagnostic performance, which is slightly better for SE. A few small studies were recently conducted with the aim of comparing the two methods in the same populations. The results were mostly in favor of SE, although SWE had a comparable value. In one study including 64 nodules, 19 of which were malignant, the qualitative SE evaluation was compared to the Mean EI value. The authors found that for a cut-off value of 38.3 kPa for the Mean EI and for Rago scores \(\geq\) 4 for the SE colormap, cancer is predicted with a sensitivity of 86.7% versus 84.4%, a specificity of 68.4% versus 79.0% and am accuracy of 81.3% versus 78.1% [47]. Another study on 185 patients compared stratification models including conventional US, SE and SWE. They concluded that SE and SWE proved to have a comparable diagnostic performance when compared in the same group and found no superiority for SE [48]. It is worth mentioning that the measurements were made on different devices. Our findings are encouraging for both techniques. The results of the two elastography assessments were very similar, but not completely superposable. Although SWE tested slightly better, the differences were not statistically significant in terms of the AUC of 0.912  
Figure 10: Illustration of false-positive elastography results in a case with Riedel thyroiditis. Appearance of hypoechoic thyroid nodule, with increased stiffness both in (**a**) shear-wave elastography: Mean elasticity index = 64.3 kPa; and in (**b**) strain elastography: entirely stiff nodule (entirely blue), Asteria score of 4 and strain ratio = 5.5.  
for the Mean EI and 0.905 for SR (\(p\) = 0.0952). In the case of SE, the value provided by the nodule-to-parenchyma or nodule-to-muscle SR proved to be a better predictor than the qualitative assessment, exhibiting the only numerical, quantitative assessment for SE. The cut-off value was established to be 3.9, similar to the previous one found in our center [35]. For the 2D-SWE evaluation, the Mean EI value was the preferred parameter. It outperformed the Max EI and QBox ratio, though all three obtained very good results. This demonstrates the superiority of a quantitative measurement of the stiffest zone in the nodule to that of a ratio.