Role of mass diffusion and water desorption on optical clearing of biological tissue immersed with the hyperosmotic agents

In order to understand the role of water desorption and mass transport process in optical clearing effect on gastric tissues with the application of hyperosmotic agents, the porcine stomach tissues (pyloric mucosa) applied topically with glycerol and dimethyl sulfoxide (DMSO) are investigated with the near infrared reflectance spectroscopy. Three solutions of 80% and 50% glycerol, and 50% DMSO are studied, all of which shows significant improvement in light transmittance and thus reduction of the light scattering of tissue. Among the solutions investigated, the best clearing effect is achieved by 80% glycerol in terms of the light penetration. Light transmittance is increased by approximately 23% and diffuse reflectance decreased by approximately 24% at 30 min after the topical application of 80% glycerol. 50% DMSO is more effective than 50% glycerol only at the beginning stage, thereafter the rate of optical clearing is slowed down with time. Although DMSO can enhance the light transmittance and thus reduce the scattering, it has a negligible effect on the imaging contrast improvement. The mass transport process of agent to tissue accounts for the different clearing effects for glycerol and DMSO, respectively. We conclude that the optical clearing by the hyper-osmotic agent is strongly correlated with the water desorption kinetics induced by agent and the agent mass transport process within tissue.