**Appendix A**

Simulation test 1 was also used to investigate the validity of compressional viscoelastography. In this investigation, we studied three groups of materials with different mechanical properties (Table A1). In group 1, *E* = 10, 20, and 30 kPa, *τ<sup>R</sup>* = 5 s, and *g* = 0.8.

In group 2, *τ<sup>R</sup>* = 1, 5, and 10 s, *E* = 10 kPa, and *g* = 0.8. In group 3, *g* = 0.4, 0.6, and 0.8, *E* = 10 kPa, and *τ<sup>R</sup>* = 5 s. For the map of each mechanical property, the simulation value (the median of the values of all elements) is compared to the theoretical value (the value of that mechanical property set in ABAQUS) using the following equation:

> error = |simulation value − theoretical value| theoretical value

Table A1 shows the results. It can be observed that the theoretical and simulation values are very close for each case. Figure 6a shows the 2D distribution map of each mechanical property and the corresponding error map for simulation test 1. It can be observed that the map for each mechanical property is perfectly homogeneous, as is the corresponding error map. The error for each element in the error map is nearly zero. The results show that the measurement is accurate, justifying the validity of compressional viscoelastography.

**Table A1.** The results of investigating the validity of compressional viscoelastography. It can be observed that the theoretical and simulation values are very close for each case.

