523 ISSN 0030-400X, Optics and Spectroscopy, 2019, Vol. 126, No. 5, pp. 523–529. © Pleiades Publishing, Ltd., 2019. Russian Text © The Author(s), 2019, published in Optika i Spektroskopiya, 2019, Vol. 126, No. 5, pp. 604–610. Use of Terahertz Spectroscopy for in vivo Studies of Lymphedema Development Dynamics 1 Yu. V. Kistenev a, b, *, V. V. Nikolaev a, c , O. S. Kurochkina d , A. V. Borisov a, b , E. A. Sandykova a, b , N. A. Krivova a , D. K. Tuchina a, e , and P. A. Timoshina a, e a Tomsk National Research University, Tomsk, 634050 Russia b Siberian State Medical University, Tomsk, 634050 Russia c Institute of Strength Physics and Materials Science, Siberian Branch, Russian Academy of Sciences, Tomsk, 634055 Russia d Microsurgery Research Institute, Tomsk, 634063 Russia e Chernyshevskii National Research University, Saratov, 410012 Russia *e-mail: yuk@iao.ru Received December 5, 2018; revised December 25, 2018; accepted January 31, 2019 Abstract—A laboratory model of lymphedema development induced by lymphatic vessel resection in rat extremities is presented. In vivo analysis of lymphedema development (monitoring for 4 weeks) employed reflective terahertz spectroscopy with a Dove prism. The incidence angle for an s-polarized electromagnetic wave directed to the boundary of the prism and the biological tissue was close to the Brewster’s angle. Signif- icant changes in the spectral characteristics of the tissue in the animals’ extremities were detected on days 21– 28 of lymphedema development. A predictive model for disease diagnostics based on monitoring the changes of the tissue absorbance curve in the 0.4–1.1 THz range was constructed. Principal component analysis and support vector machines were used in the model. DOI: 10.1134/S0030400X19050138 INTRODUCTION Lymphedema is a chronic progressive disease of the lymphatic system caused by anomalous accumula- tion of protein-rich tissue fluid, which leads to hyper- trophy of the fibrous connective tissue, adipose tissue hypertrophy, and inflammation [1, 2]. Lymphedema limits the patient’s mobility and causes severe discom- fort [3–5]. Early diagnostics of the disorder enables both the selection of appropriate treatment and the prevention of disease progression [6]. The need for methods of lymphatic system diag- nostics is increasing progressively due to the growing interest in the problems of molecular lymphology. Lymphangiogenesis is a key component of such pro- cesses as cell proliferation, directional migration of cells, cell differentiation, cell–cell interactions, tissue regeneration, and wound healing [7]. Lymphatic ves- sels play a decisive role in tumor metastasis and the rejection of transplanted organs. Conventional methods for lymphedema diagnosis are based on the registration of changes in the geomet- ric parameters of an extremity, such as its circumfer- ence (optical methods are used along with the com- mon appliances for the assessment of linear dimen- sions) or volume, which can be inferred from the volume of the displaced liquid in a reservoir where the extremity is placed. However, the precision and con- sistency of these diagnostic methods are low [8]. Intermittent pneumatic compression is a therapeu- tic approach for the reduction of lymphatic edema, which also enables the assessment of mechanical (elastic) properties of the subcutaneous tissue, disease diagnostics, and the assessment of treatment efficacy [9]. Coherent optical elastography can be used to study the elastic properties of tissue. The approach combines interference-based analysis of the spatial distribution of inhomogeneities in the tissue and the excitation of elastic waves by an ultrasound source. Coherent opti- cal elastography is noninvasive, and the elastic proper- ties of tissue can be assessed in a clinical setup if this method is used [10, 11]. However, the signal/noise ratio of the technique is rather low and the ambiguity of phase reconstruction adds complexity to the analysis. 1 The 22nd Annual Conference Saratov Fall Meeting 2018 (SFM’18): VI International Optics and Biophotonics Sympo- sium and XXII International School for Junior Scientists and Students on Optics, Laser Physics, and Biophotonics, Septem- ber 24−29, 2018, Saratov, Russia. BIOPHOTONICS