Details

Autor(en) / Beteiligte

• Elmeliegy, Abdelrahman Mohamed Ibrahiem Ali

Titel

Correlation-Based Full-Waveform Shear Wave Elastography: Towards Three-Dimensional Reconstruction of Soft Tissue Viscoelasticity

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2023

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• Soft tissue mechanical properties are strongly linked to physiology and pathology.Shear wave elastography (SWE) is used to reconstruct soft tissue mechanical properties by observing and processing shear wave motion that is commonly induced after application of an acoustic radiation force (ARF). Despite the successful application of SWE in imaging different diseases and organs, there are still several hardware and/or software limitations associated with any SWE method. For example, the mainstream SWE modalities are limited to two dimensional imaging. This is because conventional ultrasound (US) devices detect motions only in a plane. However, 2D imaging does not account for the out-of-plane scattering and does not provide a complete picture of the tissue’s geometrical and mechanical properties.Also, most of the existing SWE techniques assuming local homogeneity for convenient wave speed calculations, thus neglecting the reflections which may cause loss of important information. In addition, many existing SWE algorithms assume directional waves with local plane wave approximation. These assumptions are often violated in most circumstances involving heterogeneities. Moreover, the objective functions of the underlying reconstruction algorithms are often highly nonlinear. Also, acoustic radiation force signature and amplitude are not precisely known, thus any reconstruction algorithm that is dependent of ARF signature and amplitude would result in erroneous reconstruction. Also, it is well established that human soft tissues are viscoelastic in nature. Several existing algorithms are limited to elasticity reconstruction. However, there is increasing evidence that soft tissue viscosity can add valuable information to disease diagnosis. Motivated by the hardware and software limitations of SWE technology, in this work we address most of the challenges with an overarching goal of reconstructing 3D maps from 2D measurements (conventional SWE devices). We have approached this in a step-by-step fashion and provide several methodologies and approaches for mitigating each of them.Specifically, we first present a new reconstruction framework based on PDE constrained optimization for quantitatively evaluating soft tissue stiffness, which has the following features: (a) there is no assumption made about direction of shear wave propagation,(b) incorporates the effects of all reflections and scattering, (c) has better behaving objective function e.g., less nonlinear compared to the traditional objective functions, (d) robust even with few measurements and (e) not dependent on the ARF signature and amplitude. Ther obustness of the framework is tested in reconstruction of 2D images using synthetically generated SW motions.We then extend the new framework for reconstruction of not only the elasticity but also the viscosity map of soft tissue, by inverting the anti-plane shear visco elastic wave equation in two dimensions. We introduced several techniques to improve the reconstructed images, e.g.,multi-resolution and multi-acquisition imaging. We tested these methodologies on several different digital phantoms.We then validate the new framework using two phantom data sets of different mechanical properties. The data is acquired in three measurement planes after application of acoustic pushes, one at a time, with 3 mm between each. Only measurements at the depth of the push focus are considered, resulting in one line of measurements per plane. The three lines of measurements were then used for successfully reconstructing the out-of-plane 2D elasticity map.