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9Effect of optical clearing agents on microcirculation studied in vivo with digital capillaroscopy and laser speckle contrast imaging
A. Lugovtsov1, P. Ermolinskiy1, P. Moldon1, D. Umerenkov1, M. Maksimov1, P. Timoshina2, P. Li3, V. Tuchin2, A. Priezzhev1
1-Lomonosov Moscow State University, 1-2 Leninskiye Gory, Moscow, Russia, 119991 2- Chernyshevsky Saratov State University, 83 Astrakhanskaya str., Saratov, Russia, 410012 3- Huazhong University of Science and Technology, Luoyu Road, 1037, Wuhan, China
The optical clearing agents (OCA) are used to increase the depth of light penetration into the biological tissues and, as a result, to improve the visualization of blood capillaries in the skin and blood microcirculation assessment with speckle contract imaging technique [1]. Digital capillaroscopy is a method widely used for visualisation of human capillaries in vivo, in particular, of nail bed capillaries to identify disorders of the circulatory system at the early stages and monitoring the effectiveness of treatment [2]. The application of these methods can be enhanced by using the OCA [3]. When applied to a tissue surface, OCA penetrate inside the tissue and reduce the contribution of multiple light scattering to image formation. The mechanism of their operation is based on a decrease in the relative refractive index of optical inhomogeneities after diffuse penetration into the tissue. However, OCA penetrate to the bloodstream through the walls of capillaries in the deep layers of biological tissues. Most of OCA are osmotically active and can change the microrheological properties of red blood cells (RBC), which determine blood viscosity, that in turn can locally alter the diagnosed blood flow, introducing errors in capillary blood flow measurements using digital capillaroscopy. In this work, we examined the efficiency of 15 different OCAs for increasing the light penetration depth and improving the visualization of human nail bed capillaries. The effect of optical clearing (OC) was assessed using the OCT method on the nail bed area of volunteers' finger after the application of OCAs. The effect of OCAs on RBC aggregation and deformability properties was measured in vitro by diffuse light scattering method implemented in RheoScan device (RheoMediTech Inc., Seoul, Republic of Korea) [2]. For performing the experiments, the OCAs including fructose 50%, polyethylene glycol 300, polypropylene glycol 400, omnipaque, visipaque, accupack, glycerol, cedar oil, mineral oil, oleic acid, and various combinations of these agents were used. The effect of 4 most efficient OCAs (cedar oil, oleic acid, glycerin (98.2%), Visipaque-270) on capillary blood flow was studied by digital capillaroscopy technique.
Imaging of the nail bed capillaries showed that all OPAs except Visipaque-270 demonstrated improved image quality of the nail bed capillaries. The most effective OCA is glycerol. We demonstrated that the parameters obtained by capillaroscopy (capillary blood flow velocity and average capillary filling) of the nail bed depend on the OCA used to visualize the capillaries. We believe that the mechanism for the observed differences is most likely that OCA penetrate to capillaries and change the properties of the vessel walls and RBC. Thus, it was shown that the aggregation and deformability properties of RBC dramatically changed when blood was incubated with OCAs [3].
The obtained results demonstrate the capabilities of OC to improve the visualization of capillary blood flow and necessity to correct the parameters measured using digital capillaroscopy. These results can also be used to optimize and improve the speckle contrast imaging of the celebral blood flow. This work was supported by the Russian Science Foundation (Grant No. 23-45-00027).
[1] E. Genina, A. Bashkatov, Y. Sinichkin, I. Yanina, V. Tuchin, Optical clearing of biological tissues: Prospects of application in medical diagnostics and phototherapy. Journal of Biomedical Science and Engineering, vol. 1, pp. 22-58, (2015).
[2] A. Lugovtsov, Y. Gurfinkel, P. Ermolinskiy, A. Maslyanitsina, L. Dyachuk, A. Priezzhev, Optical assessment of alterations of microrheologic and microcirculation parameters in cardiovascular diseases, Biomedical Optics Express. vol. 10, pp. 3974-3986, (2019).
[3] P.A. Moldon, et al, Influence of optical clearing agents on the scattering properties of human nail bed and blood microrheological properties: in vivo and in vitro study, Journal of Biophotonics, pp. e202300524, (2024).
