The Study of the Microcirculation using Orthogonal Polarization Spectral Imaging

Abstract

The microcirculation is an extremely important part of the body where blood interacts with tissue to create an environment necessary for cell survival [1]. As such, an understanding of its function under both physiological and pathophysiological conditions provides real insight into the disease processes. Furthermore, as the site of interaction between blood and tissue, the microcirculation also provides the link between clinical medicine and molecular biology [1]. However, the clinical importance of the microcirculation is often overlooked due to the difficulty associated with its visualization in humans. Most observations of the microcirculation in humans have been limited to blood vessels that are visible and close to the surface, the skin and nailfold capillaries and the eye, which have found limited clinical applications [2–5]. Skin and nailfold capillaroscopy has been used in the diagnosis and treatment of peripheral vascular diseases, diabetes and hypertension [1, 2, 6]. Due to the difficulty associated with holding the eye absolutely motionless, the usefulness of microvascular measurements in the bulbar conjuctiva for clinical application in ophthalmology is very restricted [3–5]. Recently laser scanning confocal imaging has been used to study the microcirculation [7]. However, the images can only be collected at a fraction of the normal video rate, making the observation of dynamic events difficult. Furthermore, the acquisition of these images usually requires the use of fluorescent dyes for contrast enhancement [8]. Using fluorescent dyes and large, conventional microscopes, the microcirculation has been studied extensively in many animal models, and from these studies we have gained important information about its function and importance in disease states. The transfer of this knowledge directly into clinical practice has been limited due to the difficulty in quantitatively accessing the microcirculation of humans. The need for transillumination or the use of fluorescent dyes, as well as the large size of the instrumentation necessary to produce real time images of the microcirculation which can be quantitatively analyzed has prevented the widespread clinical use of techniques to directly study the micro circulation. The ability to quantitatively measure the nutritive perfusion of the vital organs in humans would have important diagnostic implications in clinical medicine.