High Resolution Cardiac Magnetic Resonance Elastography: From Phantom to Mouse Heart

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

The Microgeographical Patterns of Morphological and Molecular Variation of a Mixed Ploidy Population in the Species Complex <i>Actinidia chinensis</i>

<div><p>Polyploidy and hybridization are thought to have significant impacts on both the evolution and diversification of the genus <i>Actinidia</i>, but the structure and patterns of morphology and molecular diversity relating to ploidy variation of wild <i>Actinidia</i> plants remain much less understood. Here, we examine the distribution of morphological variation and ploidy levels along geographic and environmental variables of a large mixed-ploidy population of the <i>A. chinensis</i> species complex. We then characterize the extent of both genetic and epigenetic diversity and differentiation exhibited between individuals of different ploidy levels. Our results showed that while there are three ploidy levels in this population, hexaploids were constituted the majority (70.3%). Individuals with different ploidy levels were microgeographically structured in relation to elevation and extent of niche disturbance. The morphological characters examined revealed clear difference between diploids and hexaploids, however tetraploids exhibited intermediate forms. Both genetic and epigenetic diversity were high but the differentiation among cytotypes was weak, suggesting extensive gene flow and/or shared ancestral variation occurred in this population even across ploidy levels. Epigenetic variation was clearly correlated with changes in altitudes, a trend of continuous genetic variation and gradual increase of epigenomic heterogeneities of individuals was also observed. Our results show that complex interactions between the locally microgeographical environment, ploidy and gene flow impact <i>A. chinensis</i> genetic and epigenetic variation. We posit that an increase in ploidy does not broaden the species habitat range, but rather permits <i>A. chinensis</i> adaptation to specific niches.</p></div

Population genetic and epigenetic structure subdivisions detected in STRUCTURE.

<p>(a) <i>Actinidia chinensis</i> individuals grouped by ploidy levels and (b) sorted out by sampling sites along altitudinal changes (Low → High). The four different colors in the first row represent four main genetic clusters (<i>K</i> = 4, red: cluster I; green: cluster II; yellow: cluster III; blue: cluster IV) and three colors in the second row represent three epigenetic clusters (<i>K</i> = 3, red: cluster I; green: cluster II; yellow: cluster III).</p

Examining the Impact of Rehospitalization on Healthcare Cost of Myocardial Infarction Patients in Beijing: A Retrospective Observational Study

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Multilocus genetic and epigenetic differentiations between <i>Actinidia chinensis</i> cytotypes using analyses of molecular variance (AMOVA).

<p>*<i>P</i> values based on 10 0000 permutations</p><p>Multilocus genetic and epigenetic differentiations between <i>Actinidia chinensis</i> cytotypes using analyses of molecular variance (AMOVA).</p

The respective significances for each geo-environmental variable examined in the canonical correspondence analysis (CCA) in relation to ploidy distribution of <i>Actinidia chinensis</i>

<p>Significant codes: 0.001, **; 0.01, *. <i>P</i> values based on 999 permutations</p><p>The respective significances for each geo-environmental variable examined in the canonical correspondence analysis (CCA) in relation to ploidy distribution of <i>Actinidia chinensis</i></p

Cumulative oil recovery and water cut plots.

<p>Recycling system include 0.2 wt % VES and 0.04 wt % AOS, (a) initial water flooding; (b) recycling system flooding; (c) subsequent water flooding.</p

Interfacial tension plots.

<p>(a) IFT plots between clear fracturing flowback fluids and oil with different VES concentrations; (b) IFT plots between recycling system and oil as a function of different VES concentrations for 0.04 wt% AOS.</p

Quality analysis of formation water.

<p>Quality analysis of formation water.</p

Dynamic oscillatory plots.

<p>(a) Variations of G′ and G″ as a function of frequency (<i>ω</i>) in aqueous 70 mM C₁₆MDB/35 mM SL solution; (b) Cole–Cole plots (solid lines indicate the best fitting of Maxwell model).</p