# Shear Wave Elastography Implementation on a Portable Research Ultrasound System: Initial Results
## 3 Results
### System Validation  
Figure 7 shows the reconstructed B-mode images of various elastography phantom regions, which were obtained from the plane wave acquisitions as described in Section 2.3. Although the full reconstruction of the B-mode images was not required for the SWS map reconstruction, an inspection of the B-mode images was performed to ensure proper probe placement. It can be observed that the inclusions of stiffness that differed from the background were all visible in the B-mode images. In all cases, the contrast was poor and almost the same for all of the inclusion types and diameters. Although the B-mode imaging did not provide any information that allowed us to distinguish the inclusion type, the inclusion shapes and diameters were reconstructed very well. Therefore, the B-mode images were used to define the ROIs in the heterogeneous experiments. Figure 8 presents the shear wave motions in the homogeneous experiments, which were detected from the series of beamformed IQ data frames using the method described in Section 2.4. Each push beam generation method induced a shear wave field with distinct characteristics. In the FCUSE technique, there were three strong shear wave sources that generated shear wave fronts with the largest particle axial displacement due to having the highest push pulse length. However, the strong shear waves were o  
Figure 7: The B-mode images of the various phantom regions: (**a**) phantom region with no inclusion (background only), used in the homogeneous experiment; (**b**) type IV inclusion (70.9 kPa nominal Young’s modulus and 16.7 mm diameter); (**c**) type III inclusion (34.0 kPa and 10.4 mm); (**d**) type II inclusion (8.6 kPa and 6.5 mm). DOF, between 10-30 mm. At depths above 30 mm, the shear wave fronts were also detectable, but the particle axial velocities were smaller. The SSI technique induced broad shear wave fronts that covered most of the FOV. The lower push pulse length in the SSI method resulted in the peak axial velocity of the shear waves decreasing by an order of 5. It also caused the shear wave detection noise to become more apparent, especially at depths above 35 mm. The FCUSE-SSI method generated a wave field that combined the features of the other two techniques. Broad shear wave fronts were generated from multiple sources, which covered the majority of the FOV. In terms of shear wave peak axial velocity, the FCUSE-SSI method produced values that were lower than those from FCUSE, but higher than those from SSI. The results from the intermediate stages of the shear wave motion data filtering in the \(k-\omega\) domain are shown in Figure 9. Except for the separation of the shear waves that were propagating in opposite directions (RL and LR), the filtering in the Fourier domain (Figure 9c) allowed us to suppress the shear wave velocities that were outside of the range of interest and filter out shear waves in the low-frequency range (below 50 Hz), which improved the SNR of the shear wave motion data (Figure 9d). Since the processing of the LR and RL datasets was performed in two independent processes, portions from two ToF-based SWS reconstructions were taken for the purpose  
Figure 8: The shear wave motion data that were captured in the homogeneous experiments. Each frame shows a transient particle axial velocity map: the top row (**a–e**) shows the results from the FCUSE technique; the middle row (**f–j**) shows the results from the SSI technique; the bottom row (**k–o**) shows the results from the FCUSE-SSI technique. Note the different color map limits that were used for each technique. Images (**a,f,k**) show the first frames that were captured in each acquisition. The frame period in these images was 0.6 ms. The data after the frequency filtration are also shown. of compounding the final result, as shown in Figure 10 for the example of an SWS reconstruction of a type III inclusion using the FCUSE-SSI method. Each of the two SWS maps (Figure 10a,b) contained a part that primarily featured artifacts.