Studying Microcirculation with Micro-CT

Three&dimensional images of microvascular trees, within their surrounding tissue, are obtainable by micro&computed tomography (micro&CT) imaging of intact small animals or tissue specimens. With a resolution down to a few micrometers, these images can be used to measure the interbranch segment diameters, branching angles, volume of tissue perfused, and study the vascular anatomic relationships to organ microstructures such as glomeruli in kidney, hepatic lobules in liver, and so on. Such data can be used to model intravascular flow, endothelial shear stress, and altered branching geometry such as that which may occur in localized angiogenesis and around tissue infarction and tumors. Endothelial permeability can also be evaluated using cryostatic micro&CT methods, and special contrast agents can be used to convey permeability and vascular lumen volumes. In this chapter, we provide background information of micro&CT image systems, sample preparation methods such as ex vivo casting methods, in situ contrast agent injection techniques, special considerations pertaining to in vivo studies, and the use of probes (such as microspheres in &simulated embolization& experiments). Various image analysis approaches are discussed, such as vascular segmentation (e.g., delineating what is and what is not vasculature), measurement (e.g., the diameter of vessel interbranch segments or the hierarchical structure of the entire vascular tree), and modeling (e.g., comparing measurements to theoretical predictions based on optimization criteria, or computing perfusion territories and local shear stresses through fluid dynamic simulations). We summarize the current state of micro&CT microcirculation research and suggest possible directions for future research investigations.