Optical clearing of cranial bone by multicomponent immersion solutions and cerebral venous blood flow visualization

Background and Objectives: Optical clearing of bone tissue is of great practical interest, which opens up the possibility of the development of minimally invasive laser diagnostics and brain therapy. The aim of this work is the study of the optical clearing of cranial bone using multicomponent optical clearing agents, and the possibility of the measurement of cerebral blood flow. Materials and Methods: Optical clearing of rat skull bone ex vivo and in vivo using two solutions with different compositions and refractive indices comprising ethanol or thiasone as biological tissue permeability enhancers, has been studied in the paper. Kinetics of collimated transmission of the bone samples under the influence of these solutions has been measured in the spectral range of 600-900 nm, and Doppler optical coherence tomography (DOCT) of rat cerebral vessels has been carried out. Results: Within 4 hours, a relative increase in the collimated transmittance under the action of the immersion solutions with inclusion of ethanol and thiasone by 15% and 80%, respectively, has been obtained. The effectiveness of optical clearing of bone tissue has been 4.5$\pm$0.4% and 13.2$\pm$3.4%, respectively. The use of the solutions has contributed to significant improvement of visualization of vena cerebri magna using DOCT without damage of the cranial bone and allowed determining the velocity of blood flow in the vein in the normal state (7 mm/sec) as well as under the action of adrenaline (5.5 mm/ sec). Conclusion: Thus, it is shown that the use of these solutions increases the probing depth of DOCT and improves the imaging of cerebral blood vessels, which can be used in the diagnosis of various pathological changes, including blood disorders.