This book introduces orthogonal polarized spectral (OPS) imaging, a new technique for examining the microcirculation in both animals and humans during surgery and in other clinical setups. OPS imaging creates an image by using the sub-surface scattering of polarized light to create a 'virtual' light source within the tissue being observed. Thus, the microcirculation can be visualized without the use of fluorescent dyes or transillumination, making it possible to observe the human microcirculation in real time. The technology has been incorporated into a small, hand-held device called a CYTOSCANTM video microscope, which can be used in both research and clinical settings. Several validation studies comparing OPS imaging against standard intravital fluorescence microscopy in animal models demonstrate that it is possible to make quantitative measurements of relevant parameters (vessel diameter, red blood cell velocity and functional capillary density) from these images. Further studies show the feasibility of making such measurements in various human organs such as the skin, intestine, and brain. In addition, this book presents several clinical applications including use in cardiopulmonary bypass, neurosurgery, intensive care, general surgery and plastic surgery. The book should be read by anyone concerned with microvascular perfusion. This includes not only those involved in microcirculation research but clinicians interested in nutritive perfusion. The technique described here will be of aid to a variety of surgical specialists from cardiac and neurosurgeons to plastic surgeons. It will likewise be of interest to angiologists, anesthesiologists, neonatologists, dermatologists, and general surgeons.