Optical clearing of blood

Light scattering in biological tissues and blood leads to a reduction in imaging spatial resolution, imaging depth and contrast of optical imaging techniques. Refractive index mismatch between erythrocytes and blood plasma is the main source of light scattering in blood. Immersion method for optical clearing of biological tissues and blood can be applied to improve light transport. Application of biocompatible clearing agents can lead to reduction of light scattering in turbid biological samples and enhancement of optical penetration depth in tissues and blood. The mechanism of the enhancement of transmittance depends on the particular agent applied, its concentration and stage of the measurements. Determination of optimal type and concentration of clearing agents for blood optical clearing is required for effective and non-destructive usage of optical clearing techniques. The purpose of this work is to investigate systematically the mechanism of optical clearing of blood by use of various biocompatible clearing agents and determination of the optimal type and concentration of clearing agents for blood optical clearing in order to improve light penetration depth for optical imaging techniques. The experiments carried out on animals showed the possibility of in vivo applications of optical clearing method. The scattering and absorbing properties of blood are determined by the optical properties of hemoglobin. The knowledge of refractive index of human hemoglobin is important for practical applications in blood and tissue optics. The direct measurements of refractive index of oxygenated and deoxygenated hemoglobin in wide range of concentrations were carried out in visible and near infrared region. The suggested model functions allow to estimate the refractive index of hemoglobin with arbitrary concentrations, including highly concentrated hemoglobin as in blood and in erythrocytes.