Structural Analysis Of Cardiovascular Tissue Using Quantitative Polarised Light Microscopy

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Whittaker, Peter
Biophysics; General
thesis / dissertation description
Prior to the advent of electron microscopy, polarised light was commonly used in structural research. New microscopical and mathematical methods have made the techniques worthy of reappraisal. I used quantative polarised light microscopy to examine tissue structure at both the fibre and molecular level. Birefringent materials, those with an anisotropic molecular organisation (such as collagen, muscle and elastin), can be studied using polarised light. The optical properties of birefringent materials were used to determine fibre orientation. Two-dimensional orientation was measured on the planar rotating microscope stage and three-dimensional orientation on a Universal stage. Molecular organisation, which affects optical anisotropy, was assessed by measuring the path-difference or retardation when linearly polarised light passes through birefringent materials. Five projects, focussing on collagen and muscle in cardiovascular tissues, were undertaken to demonstrate the usefulness of polarised light microscopy in structural studies.;I measured the two-dimensional orientation of cardiac muscle fibres in hypertrophic cardiomyopathy and developed a quantitative method to complement the current qualitative method of diagnosis. I used the Universal stage to measure the orientation of collagen fibres in brain arteries and found that the fibres were predominantly circumferentially aligned at normal systolic pressures, but, at higher pressures a population of fibres had large longitudinal components of orientation. I measured the retardation in scar collagen produced following myocardial infarction and found that changes in the optical properties of collagen could be detected for at least six weeks after its production. A measured difference in retardation in tendons from floppy mitral valves, indicated that degraded collagen can also be detected using polarised light. Both fibre orientation and molecular organisation were assessed in cerebral saccular aneurysms. The aneurysm wall was layered and the collagen fibres were organised in a complex three-dimensional weave, suggesting a strong structure; however, the retardation in the aneurysm was lower than normal, indicating less molecular organisation and a possible reason why aneurysms enlarge and rupture.;The general conclusion is that quantitative polarised light mircoscopy remains an effective method in structural analysis.