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A fiber-based, label-free multispectral fluorescence lifetime imaging and intravascular ultrasound (FLIm/IVUS) system was evaluated as a new tool for monitoring variations in biochemical and structural composition of vascular biomaterials, including native arteries and engineered vascular grafts both in vitro and in vivo. Fiber-based FLIm was adapted to assess the hollow geometry of vasculature, allowing for imaging of the luminal surface of vessels. The capacity of FLIm to resolve tissue cellular location (i.e. scaffold reendothelialization) and collagen to elastin ratio on the vessel wall was investigated. Quantitative imaging parameters derived from spectrally- and temporally-resolved autofluorescence (i.e. intensity ratios and fluorescence lifetime) provide benchmark indicators to identify areas of recellularized tissue, and to distinguish wall matrix compositions within and across biomaterials. In addition, fiber-based FLIm was complemented with intravascular ultrasound (IVUS) for simultaneous in vivo evaluation of biochemical and structural tissue properties. Here, we performed an in vitro evaluation of pig carotid arteries and show correlations between FLIm parameters and biochemical composition in different anatomical locations. We discuss the spectral and lifetime differences between native pig carotid artery, acellular antigen removed bovine pericardium grafts, and reendotheliarized grafts. Finally, we translate the findings to an in vivo clinical FLIm/IVUS imaging study with antigen removed bovine pericardium grafted on healthy pig native carotid artery. Upon implantation, the graft is expected to repopulate with cells, and change composition as cells remodel it. These experiments demonstrate the feasibility of fiber-based FLIm/IVUS to examine vascular engineered tissue in research and clinical settings.
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