Publikationsdatenbank

Studies of microstructural changes of liver tissue by magnetic resonance elastography and diffusion-sensitive magnetic resonance imaging (2022)

Art

Hochschulschrift

Autor

Krehl, Karolina (WE 12)

Quelle

Berlin, 2022 — IX, 73 Seiten

Sprache

Englisch

Verweise

URL (Volltext): https://refubium.fu-berlin.de/handle/fub188/37282

Kontakt

Institut für Tierpathologie

Robert-von-Ostertag-Str. 15
14163 Berlin
+49 30 838 62450
pathologie@vetmed.fu-berlin.de

Abstract / Zusammenfassung

The liver is a vital organ that is involved in most processes in the body and rapidly adapts to changes in the organism. Pathological and physiological processes are associated with adaptations of the cellular and noncellular (extracellular matrix) tissue components, which can be visualized by medical imaging such as elastography and diffusion-sensitive magnetic resonance imaging. The relationship between microarchitectural changes and the corresponding biophysical manifestations is not yet clear. Elastography is already a standard clinical procedure in liver diagnosis, which requires a deeper understanding of the influence of structural elements on macroscopic imaging properties. In order to properly diagnose pathological processes, with special attention to the early detection of chronic liver diseases such as fibrosis or nonalcoholic fatty liver disease, we must first focus on physiological changes to understand the results of modern imaging techniques. In this work, we studied ex vivo rat livers to determine how structural changes of the liver depend on postmortem time and blood content on the one hand, and to investigate liver adaptation to physiological gestation on the other. We identified three phases in the cascade of postmortem biological events that provide a biophysical imaging fingerprint of liver tissue breakdown. Within the first two hours after death, the viscoelastic properties and also the water diffusion capacity of the liver change rapidly due to cytotoxic edema manifested by enlargement of hepatocytes. This is followed by a stable phase up to ten hours post mortem. In the final phase, the degradation phase, there are changes in cell shape, cell packing pattern, and loss of cell membrane integrity, resulting in higher water diffusivity and an increase in the wave penetration rate. In this study, we demonstrated the individual contributions of vascular components and cellular integrity to the changes observed with imaging techniques. In the second part of this work, we investigated pregnancy-induced changes in microstructure and biophysical properties in the liver. We used the findings from the first study to minimize the effects of additional factors as much as possible. To this end, liver samples were examined under identical conditions during the stable phase - beginning two hours post mortem. Our findings demonstrate that the adaptations of the female organism during pregnancy lead to liver hypertrophy and hyperproliferation of hepatocytes, which cause increased intracellular pressure, increased mechanical resistance, and a decrease in intracellular spaces, resulting in an increase in liver stiffness and wave penetration rate. Due to hypertrophy, cell density per unit area decreases, and fewer cell membranes (which act as barriers to water movement) are present, resulting in an increase in water diffusivity in the livers of pregnant rats. Elastography and diffusion-weighted imaging can detect microstructural changes in liver tissue, and the results of this work provide insight into the processes that affect the biomechanical properties and diffusivity of biological tissue and form the basis for further investigation.