Investigation of Strain Elasstography to Assess Benign and Malignant Tumors

Abstract

Poroelastography is a new subfield of ultrasound elastography that enables cost-effective and non-invasive imaging of mechanical properties of tissues. Assessment of changes in the mechanical properties of tumors is of great clinical significance as the onset of pathology often triggers these changes. Interstitial fluid pressure (IFP) and Solid stress (SS) are clinically significant tumor parameters in cancer initiation, growth, and metastasis. Although IFP and SS are crucial parameters for cancer prognosis and treatments, there are currently no non-invasive methods to assess this parameter in vivo. The use of poroelastography to noninvasively assess IFP and SS in cancers has not been thoroughly investigated yet. In this thesis, we used a novel Finite element modeling (FEM) technique to examine the effect of IFP and SS on elastographic strains generated inside a tumor model in a poroelastography experiment, including fundamental strains (normal and shear strains) and derived strains (principal and Von Mises strains). A variety of simulated phantoms with different properties of backgrounds and inclusions are simulated. We proposed the first principal and the Von Mises strain as sensitive elastographic markers associated with IFP and SS changes in simulated cancers. Our simulation results show that SS causes shear strains inside the tumor and leads to spatial variations in derived strains, while IFP causes uniformly reduction in derived strains. Using ultrasound simulations, we demonstrated that the observations from the FE study are also applicable with noisy experimental conditions except for the radial shear strain and the second principal strain. Additionally, as a proof of concept, this study used previously obtained mice data to demonstrate the feasibility of imaging Von Mises strains in vivo. This study may help understand the effect of IFP and SS on the strains generated in a tumor during a poroelastography experiment and may also result in new methods to check for IFP and SS in cancers in vivo.