## 3 Elastographic Methods
### Point SWE (pSWE)  
The technique has been described in detail in the EFSUMB and WFUMB guidelines [1; 2; 4; 6]. [PERSON] et al. reported that pSWE and magnetic resonance elastography (MRE) values correlated well in patients with a body mass index (BMI) of less than 30 kg/m\({}^{2}\) and minimal US data dispersion; increasing US data dispersion was directly related to a higher BMI [27]. In another study, SWVs differed between normal-weight and obese children (1.08 \(\pm\) 0.14 versus 1.44 \(\pm\) 0.39 m/s; \(p\) < 0.001), but not by gender. Multivariate linear regression demonstrated that the shear wave velocities (SWV)s were primarily associated with age in normal-weight children (\(p\) < 0.05) and with BMI in obese children (\(p\) < 0.001). In the obese group, mean SWV was significantly higher in children with abnormal echogenic livers than in those with livers of normal appearance (1.53 \(\pm\) 0.38 vs. 1.17 \(\pm\) 0.27), \(p\) < 0.05. The difference was not significant in the normal-weight group [58]. In the study of [PERSON] et al., which included 132 patients 0-17 years, the mean value of SWV was 1.16 (0.14) m/s. Neither age (\(p\) = 0.533) nor depth of measurement (\(p\) = 0.066) had a significant influence on SWV, whereas a significant effect of gender was found, with lower values in females (\(n\) = 71, \(p\) = 0.025); however, there was no significant interaction between age groups (before or after puberty) and gender (\(p\) = 0.276). There was an inter-lobar difference with lower values in the right liver lobe compared to the left (1.14 \(\pm\) 0.22 m/s vs. 1.19 \(\pm\) 0.28 m/s, \(p\) = 0.036) and with a significantly lower variance in the right lobe (\(p\) < 0.001). Consistent values were measured by different examiners (\(p\) = 0.108); however, the inter-examiner variance deviated significantly (\(p\) < 0.001) [59]. SWV measurement was feasible in children at any age with acceptable reliability. The depth of measurements in the liver seemed to have no influence on the results. There was no statistical difference between measurements taken at different ages, with a mean SWV of 1.12 m/s (range: 0.73 to 1.45 m/s) [60]. In another study, mean SWV in the right liver lobe was 1.07 \(\pm\) 0.10 m/s. No significant differences were found according to sex or among different probe locations [61]. SWVs were, however, significantly higher in the left liver lobe in comparison to the right lobe (1.07 \(\pm\) 0.10 m/s, right; 1.21 \(\pm\) 0.16 m/s, left). The depth of measurements also influenced the SWV values, being slightly lower at deeper locations. Regarding the age, significant differences were found for children \(<\)6 years old compared with other age groups. SWV seems to be influenced by age, depth, and measurement location. A mean SWV of 1.07 \(\pm\) 0.10 m/s for a healthy pediatric population with the possibility of reaching 1.12 m/s in the case of younger children was found. SWV values were more consistently obtained when assessing the right liver lobe and at depths lower than 5 to 6 cm [61]. pSWE and 2D-SWE values were able to detect high-grade histopathological fibrosis and had high success rates when distinguishing high-grade from low-grade fibrosis. In a series of 75 children, SWV cut offs were 1.67 m/s for pSWE and 1.56 m/s for 2D-SWE in detecting fibrosis or inflammation and 2.09 m/s for pSWE and 2.17 m/s for 2D-SWE in discriminating children with low and high histological liver fibrosis scores. However, both techniques had limited success rates when differentiating low-grade fibrosis from normal liver tissue [14]. In another prospective study, pSWE was feasible in children using both the convex and the linear transducers. Mean SWV measured in the right lobe was 1.19 \(\pm\) 0.04 m/s with the convex transducer and 1.15 \(\pm\) 0.04 m/s with the linear transducer. Age had a small effect on the measurements. BMI and gender had no significant effects on SWV, whereas site of measurement had a significant effect, with lower SWV values in the right hepatic lobe.