The high scattering nature of non-transparent human tissue limits the imaging depth of optical coherence tomography (OCT) to 1-2 millimeters. By using the longer wavelength of the light source, the penetration depth is improved; the imaging contrast is however decreased largely due to the reduced backscattering in microscopic scale and the reduced refractive heterogeneity in macroscopic scale. For more effective diagnosis using OCT, a concurrent improvement of penetration depth and imaging contrast are often needed. We report in this paper that the OCT imaging depth and contrast can be enhanced concurrently by the use of osmotic agents. We demonstrate experimentally, by examples, that the topical applications of glycerol and propylene glycol, two common biocompatible and osmotically active solutions, onto the tissue surfaces could significantly improve the OCT imaging contrast and depth capability. The biotissues demonstrated include the rat skin, human oesophageal and gastric tissues.
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