## 5 Experimental Study Using Phantoms and Results  
In order to pre-determine materials for measurement with the FibroScan(r) head, a series of tests were performed. Four CIRS Model 039 phantoms were used, all filled with Zerdine(r) gel but differing in [PERSON]'s modulus values (0.85 kPa, 6.67 kPa, 15.76 kPa, 32.49 kPa). The average ultrasound velocity for all phantoms was similar, at around 1538 m/s. A comparable level of contrast of the speckle imaging of the healthy liver was also maintained. First, control measurements were performed, where the universal M-type (3.5 MHz) head of the FibroScan(r) device was applied directly to the foil-protected surface of the phantom. During the test, the measuring tip was mounted on a specially prepared tripod (Figure 16) so that a constant pressure force was maintained and its position was perpendicular to the phantom surface. This design made it possible to achieve satisfactory repeatability of results. Distilled water was used as a medium to ensure good mechano-acoustic coupling. The study was carried out for four CIRS phantoms, but for the one characterized by the lowest [PERSON]'s modulus value (0.85 kPa), no measurement was possible. The FibroScan(r) device has a measurement range of 1.5-75.0 kPa, meaning it does not include the value for this model in its range. The results of the obtained elastic modulus and damping values for the other three phantoms are shown in Figure 17.  
Figure 15: Wave velocity combination diagram for different forcing frequencies. Analysis of the results obtained allows us to conclude that the results for the phantom with the lowest value of Young's modulus of the three tested (6.67 kPa) were underestimated by about 19%. For the medium stiffness, the error oscillated around 12%, and for the highest stiffness, an overestimation of 47% was achieved. It was found that as the stiffness of the phantom increases, the spread of the results increases. The results obtained allowed the thesis that the thickness of the selected materials should be as small as possible, so that the unfavorable value of wave attenuation does not occur. The next stage of the study was to check the commonly used materials allowing measurement with the FibroScan(r) device on CIRS phantoms. Samples were made of materials such as Agar Progel, Medical Gel #0, and Ecoflex 00-20 silicone rubber for later construction of overlays [15; 16; 17]. The prepared samples were placed between the head and the surface of the phantom, additionally protected by a film. Example photos of the realization of measurement tests of designed and fabricated attachments of different thicknesses on CIRS Model 039 phantoms using the FibroScan(r) apparatus are shown below (Figure 18). Figure 16: The method of fixing the head for control measurements with the FibroScan® device. Figure 17: Overview of transverse and ultrasonic wave propagation images recorded with the FibroScan® device for three phantoms from CIRS (fabric Young’s modulus: 6.67 kPa, 15.75 kPa, 32.49 kPa). In order to evaluate the suitability of selected shapes and thicknesses of D_0 and E_15 attachments of Agar Progel, Medical Gel #0, and Ecoflex 00-20 materials, this chapter compares the average values of stiffness and ultrasound attenuation measurements of CIRS Model 039 phantoms E = 6.67 kPa and 15.75 kPa, as well as images of 50 Hz transverse wave propagation and a 3.5 MHz ultrasonic wave recorded with the FibroScan(r) device (Figures 19 and 20). Analysis of control measurements of the target developed D_0 and E_15 attachments from all three target materials selected for testing (Agar Progel, Medical Gel #0, Ecoflex 00-20) confirms their correct performance as a mechanical-acoustic simulation of the intermediate layer between skin and liver tissue.