Date of Award

2019

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy in Biomedical Engineering (PhD)

Administrative Home Department

Department of Biomedical Engineering

Advisor 1

Jingfeng Jiang

Committee Member 1

Bruce Lee

Committee Member 2

Sean Kirkpatrick

Committee Member 3

Gowtham

Abstract

Ultrasonic elastography (UE) is a set of ultrasonic imaging techniques used to noninvasively quantify material properties of soft tissues. UE comes in two major forms, strain elastography (SE), in which compressional force is used to produce strain images of human tissues, and shear wave elastography (SWE) in which dynamic excitation is used to induce shear waves and (typically group) shear wave speeds (SWS) are collected from their propagation. Clinical interest in UE lies in its potential for noninvasive screening for pathologies with associated biomechanical property changes, such as breast lesion classification and staging of liver fibrosis. The diagnostic utility of UE hinges on its ability to consistently detect and characterize the underlying mechanical properties of diseased and healthy tissues. A fair amount of analysis and effort has been invested in investigating signal processing and measurement related uncertainty in SWE and SE. Comparatively less attention has been paid to investigating the uncertainty associated with the complex and multifaceted continuum biomechanics that underlies the response of tissue to an UE measurement.

This dissertation contains my contributions toward delineating the role of several of these biomechanical facets on UE measurements. Its chapters are composed of a collection of five articles. In the first article, we investigated the contrast transfer characteristics of an advanced form of SE called viscoelastic imaging through mechanical simulations, which was found to be influenced by the non-viscous material characteristics. This motivated a follow up simulation study were we applied a systematic design-of-experiments based approach to determine the material and user dependent factors that most strongly influence traditional SE contrast. We found that along with the initial elasticity of the tissue, elastic nonlinearity and precompression seem to play substantial roles in SE contrast.

The other three articles contain my contributions to SWE. Here, a robust approach to SWS estimation based on the method-of-characteristics solution to the 1D elastic wave equation was developed. I also contribute to the theoretical development of acoustoelastic analysis in SWE. From these efforts, it was found that only certain material models could accurately represent SWS along multiple principle axis of deformation and that acoustoelastic analysis can be applied to understanding SWE measurements in the presence of fluid-induced deformation.

Available for download on Friday, July 31, 2020

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