High Resolution Cardiac Magnetic Resonance Elastography: From Phantom to Mouse Heart
thesisposted on 16.02.2016 by Yifei Liu
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First proposed in 1995, magnetic resonance elastography (MRE) has attracted more and more attention with its capability of estimating soft tissue stiffness non-invasively. In addition to the FDA-certified application for hepatic disease diagnosis, MRE has been studied in multiple organs as a potential new biomarker in various disease diagnoses, especially in recent years. Beside the application to disease diagnosis, MRE has also been utilized in monitoring the development of engineered tissue and in more fundamental studies of tissue viscoelasticity. This dissertation aims to advance the application of high field MRE on complex anatomical structures, beginning with phantom studies progressing to, arguably, the most complex application yet attempted, cardiac MRE in vivo on a mouse model to assess myocardial stiffness in healthy and pathological subjects. Prior to attempting in vivo cardiac MRE on the mouse model, several pilot studies were conducted on phantom models to advance the technique. A wideband phantom study was conducted to improve viscoelastic model identification. In order to better understand mechanical wave motion in geometry similar to the left ventricle, MRE experiments on a liquid-filled spherical shell phantom embedded in a soft tissue mimicking material were also conducted. Computational finite element simulations on a three dimensional model of a mouse with different actuation methods were also performed to improve understanding of how mechanical waves propagate into the complicated geometry of the mouse body, and how the tissue responds under different actuation approaches. An in vivo mouse cardiac MRE technique was then developed and tested on a healthy mouse model. This technique is able to track expected stiffness changes in the myocardium as a function of the cardiac cycle. And the results showed the feasibility of this implementation of in vivo cardiac MRE on mice. A follow-up study of applying the cardiac MRE on a Myocardial Infarcted (MI) mouse model was then conducted to assess the ability to noninvasively quantify expected changes in the myocardial mechanical properties of these animals, relative to the healthy cases.