Small blood microvessels can be clearly identified visually by the naked eye in in vivo study of hamster and rat skin, when a transparent window in the skin was created by glycerol drops applied to the subdermal side of a native hamster dorsal skin flap window preparation, or by intradermal injection of glycerol or 40% glucose (see Fig. 34).
In in vitro study of fresh human fat tissue with a topical application of a propylene glycol (PG) solution (50â80% with pure water), blood vessels are also seen. In order to have a quantitative sense of fat tissue optical clearing, the corresponding OCT images were registered (see Fig. 58). Two images of a fat sample without and with topical application of PG solution were captured. It is well seen that OCT techniques are very capable of visualizing the fat cells because of their sizes, which are within the limits of the OCT system spatial resolution. By comparison of images of Figs. 58(a) and 58(b), the light penetration enhancement is evident. Particularly, the blood vessel wall is clearly visualized after the topical application of PG solution, whereas without application of chemical agents, the light is almost blocked by the blood vessel. This is due to the fact that the blood inside the vessel highly scatters the incoming light, which degrades the imaging performance.
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