ИСТИНА

Water content estimation in biotissues is of paramount importance for a large amount of clinical applications due to inevitable role of water in metabolic processes starting from the cell-level metabolism ending the bioprocesses of the whole human body [1]. For example, hydration status of skin layers correlates directly with aging processes and mechanical elasticity of skin. Alterations of water content in tissues can be a concomitant symptom of number of serious disease, such as heart failure or impaired renal function [2]. Or, as it was demonstrated in [3, 4], water concentration in tissues can be used as an accurate descriptor, that allows one to classify between tumor and healthy tissues. Among methods, that allows one to determine hydration level of tissues, optical techniques are of great interest due to their low invasiveness and precision of the obtained results. Optical methods that determines water concentration can be used for intraoperative guidance on exposed tissues[3,4] as well as for purely non-invasive measurements. For example, in the work [5], the possibility of deep-tissues’ temperature measurement by means of diffuse optical tomography was demonstrated, while in the work [6] fraction of bound water in tissues was estimated by water absorption bands in near-infrared region, which is good agreement with diffuse weighted magnetic resonance imaging, thereby demonstrating the ability of optical methods to compete even with MRI. Indeed, water concentration in tissues can be determined by several optical methods: Raman spectroscopy [7], diffuse reflection spectroscopy [8], optical microscopy [9] — however, it remains unclear whether the signals obtained by different optical methods provide the same information. Whether these methods are complementary to each other or just one of them is sufficient. In this work, we compared several optical methods of water content determination — Raman spectroscopy, diffuse reflection spectroscopy of the near-IR range, using various water absorption lines (980, 1200, 1450 nm), optical capillaroscopy on a number of physiological models in vivo, and also using optical phantoms of biological tissues. We assessed the possibility of using water absorption lines in the near IR range and the valence band of Raman water scattering to assess the fraction of bound water in tissues using the simplest fiber schemes suitable for use in a clinic. Other possibilities and disadvantages of these optical methods for determining the water content in tissues are evaluated. References 1. Asogwa C., Lai D. // Electronics 6, 82 (2017). 2. Cho S., Atwood J. E. // Am. J. Med. 113, 580–586 (2002). 3. Barroso E. et al. // Anal. Chem. 87, 2419–2426 (2015). 4. Barroso E. M. et al. // Cancer Res. 76, 5945–5953 (2016). 5. Chung, S. H. et al. // J. Innov. Opt. Heal. Sci. 4.04 (2011): 361-372. 6. Chung, S. H. et al. // J. Biomed. Opt. 17.7 (2012): 071304. 7. Choe, C.S. et al. // Analyst 141.22 (2016): 6329-6337. 8. Yakimov, B. P. et al. // Quantum Electronics 50.1 (2020): 41. 9. Shirshin E.A. et al. // J. Biophotonics11.9 (2018): e201800066