A Novel Finite Element Model to Assess the Effect of Solid Stress Inside Tumors on Elastographic Normal Strains and Fluid Pressure

Ultrasound elastography is a noninvasive imaging modality used to assess the mechanical behavior of tissues, including cancers. Analytical and finite element (FE) models are useful and effective tools to understand the mechanical behavior of cancers and predict elastographic parameters under different testing conditions. A number of analytical and FE models to describe the mechanical behavior of cancers in elastography have been reported in the literature. However, none of these models consider the presence of solid stress (SS) inside the cancer, a clinically significant mechanical parameter with an influential role in cancer initiation, progression, and metastasis. In this paper, we develop an FE model applicable to cancers, which include both SS and elevated interstitial fluid pressure (IFP). This model is then used to assess the effects of these mechanical parameters on the normal strains and the fluid pressure, estimated using ultrasound poroelastography. Our results indicate that SS creates space-dependent changes in the strains and fluid pressure inside the tumor. This is in contrast to the effects produced by IFP on the strains and fluid pressure, which are uniformly distributed across the cancer. The developed model can help elucidating the role of SS on elastographic parameters and images. It may also provide a means to indirectly obtain information about the SS from the observed changes in the experimental elastographic images.