# Shear Wave Elastography Implementation on a Portable Research Ultrasound System: Initial Results
## 3 Results
### Heterogeneous Phantom Experiments  
The ability to detect inclusions with stiffnesses that were both higher and lower than that of the background was also tested using a phantom. Three out of the four available target stiffness values were chosen for these tests, with nominal Young's moduli of 8.6 kPa (type II), 34.0 kPa (type III) and 70.9 kPa (type IV), which (using Equation (2)) corresponded to nominal shear wave speeds of 1.69 m/s, 3.37 m/s and 4.86 m/s, respectively. The background material had a Young's modulus of 16.7 kPa, which mapped to an SWS of 2.36 m/s. In the experiments, target diameters of 16.7, 10.4 and 6.5 mm were used, centered at a depth of 30 mm. B-mode imaging was used to find the probe position that produced an inclusion that was centered in the FOV. In the case of the type IV inclusion, this probe placement was not possible due to the mechanical design of the phantom; thus, the inclusion was shifted slightly to the right. The results of the heterogeneous phantom experiments are presented in Figures 12-14. The detailed results are listed in Tables A1-A3 in the Appendix A. A visualization of the SWS estimates for the inclusions is shown in the form of bar plots in Figure 15.  
dropped from 4.42 m/s to 3.38 m/s between the inclusion diameters of 16.7 and 6.5 mm, thereby dropping by nearly 24%. All of the results were biased low, by a minimum of 7.9% for inclusion size 16.7 mm to a maximum of 30.4% for smaller diameters, whereas the background SWS estimate was biased high, by 7.3% to 16.8%. The FCUSE-SSI technique suffered the highest background SWS estimate bias. Although the inclusion SWS bias was similar in all techniques, the SSI method consistently showed the lowest background SWS estimation bias compared to the other methods. The SSI method also showed the lowest background SWS estimation bias. Figure 12: The results of the heterogeneous phantom experiments for the type IV inclusion (Young’s, modulus of 70.9 kPa, which corresponded to a nominal SWS of 4.86 m/s): the top row (**a–c**) shows, the results from the FCUSE technique; the middle row (**d–f**) shows the results from the SSI technique; the bottom row (**g–i**) shows the results from the FCUSE-SSI technique. The detailed quality metrics can be found in Table 1 in the Appendix 1. Due to the smaller nominal SWS difference between the inclusion and the background material, the type III inclusion SWS maps (Figure 13) showed worse contrast than those in the previous case. The same trend could also be observed, with the inclusion SWS estimates decreasing along with the inclusion diameter for all of the examined techniques. For the smallest inclusion size, this made the inclusion barely detectable in the image as the artifacts in the background were of comparable sizes and signal levels. Out of all of the techniques used, FCUSE produced the best inclusion SNR, while FCUSE-SSI produced the best background SNR. No strict trend was observed for the other characteristics. In the case of the type II inclusion SWS maps (Figure 14), all of the inclusions could be seen easily as the low SWS value of the inclusion material did not appear in any other image region. In contrast to the previous two cases, the type II inclusion images exhibited a reverse trend of the inclusion diameter effects on the SWS estimates. Here, the inclusion SWS estimates increased with a decreasing inclusion diameter. In addition, all of the results were biased high. Figure 13: The results of the heterogeneous phantom experiment for the type III inclusion (Young’s modulus of 34.0 kPa, which corresponded to a nominal SWS of 3.37 m/s): the top row (**a–c**) shows the results from the FCUSE technique; the middle row (**d–f**) shows the results from the SSI technique; the bottom row (**g–i**) shows the results from the FCUSE-SSI technique. The detailed quality metrics can be found in Table 10 in the Appendix 11.