Effect of dextran-induced changes in refractive index and aggregation on optical properties of whole blood.

The purpose of the present study is to investigate systematically the mechanisms of alterations in the optical properties of whole blood immersed in the biocompatible agent dextran, and to define the optimal concentration of dextrans required for blood optical clearing in order to enhance the capability of light penetration depth for optical imaging applications. In the experiments, dextrans with different molecular weights and various concentrations were employed and investigated by the use of the optical coherence tomography technique. Changes in light attenuation, refractive index and aggregation properties of blood immersed in dextrans were studied. It was concluded from the results that the mechanisms for blood optical clearing are characteristic of the types of dextrans employed, their concentrations and the application stages. Among the substances applied, Dx500 at a concentration at 0.5 g dl(-1) gives the best result in improving light penetration depth through the blood. The increase of light transmission at the beginning of the addition of dextrans is mainly attributed to refractive index matching between the scattering centres and the ground matter. Thereafter, the transmission change is probably due to a dextran-induced aggregation-disaggregation effect. Overall, light scattering in the blood could be effectively reduced by the application of dextrans. It represents a promising approach to increasing the imaging depth for in vivo optical imaging of biological tissue, for example optical coherence tomography.