Real-time imaging offers a powerful diagnostic tool to evaluate the many endothelial functions in an organism. Although the clinical use of real-time imaging of the endothelium is in its infancy, the use of this tool in diagnosing endothelial dysfunction in animal models is widespread and, in many cases, state-of-the-art.

The initial attraction of real-time imaging was the “wow factor.” A picture tells a thousand words – and a movie is even better! Seeing images that put in place concepts that previously were only imagined is a powerful tool.

But the real attraction of real-time imaging of the endothelium is that it allows for the spatial and temporal evaluation of experimental systems that are at a higher order of complexity (1) compared with traditional static assays. Historically, ignoring such complexity has impeded progress in endothelial research. Although studying protein structure in a crystal is complex and no doubt yields useful information, the function of that protein in a membrane, let alone in a cultured cell, is not always predictable. Similarly, the response to a stimulant of endothelial cells (ECs) in culture does not predict the response of ECs in vivo. Real-time imaging provides a window into functioning endothelium in the context of its native microenvironment (Table 177–1).

The aim of advancing technology is to allow observations in the natural, undisturbed environment. Until this is optimal, imaging of the endothelium has tended to suffer “the observer's paradox,” in which the observation affects the outcome. To obfuscate this has often meant that real-time imaging of the endothelium is limited to the microcirculation of organ surfaces or thin tissues, with a few exceptions.