The aim of the study was to evaluate a novel non-invasive method-optical coherence elastography (OCE)-for detecting early changes in the elasticity of tumor tissue in response to chemotherapy. Materials and Methods. Female BalB/C mice were used in this experimentation. Cultured breast cancer cells (the 4T1 line) were implanted onto the surface of the mouse ear. The experimental animals were randomly separated into two groups: the control group (n=5) and the therapeutic group (n=5); the latter one received chemotherapy with cisplatin injected intraperitoneally at a dose of 6 mg/kg. We then studied the elastic properties of the tumor tissue using a spectral multimodal optical coherence tomograph (Institute of Applied Physics of the Russian Academy of Sciences, Russia) that allowed for measuring the mechanical characteristics in terms of elastography. The compression mode of the OCE is based on estimating the inter-frame variation gradient of the OCE signal phases when tissue images are pairwise compared in the process of tissue deformation. By using a silicone layer for calibration we were able to determine the absolute values of the tissue stiffness (the Young's modulus of elasticity). The stiffness distribution across the tissue sample is displayed by images with a pseudocolor palette. Results. The efficacy of chemotherapy with cisplatin was evaluated by the standard technique (kinetics of tumor growth), and then verified by histological analysis. Throughout the study, the tumor growth rate in the control group was significantly (p<0.05) higher than that in the therapeutic group. By means of OCE significant differences (p<0.05) in the stiffness of the tumor tissue were found between the therapeutic and control groups of animals already on day 5 after the start of chemotherapy. By the end of the treatment, the OCE showed the lowest values of tumor stiffness, which correlated with the existence of extensive necrosis as confirmed by histology. Conclusion. During chemotherapy, OCE can be used for in vivo monitoring of tumor stiffness as an index of treatment efficacy.

New modalities of optical coherence tomography (OCT) are based not only on the analysis of light beam scattering by biological tissues, but also, to a greater extent, on the assessment of spatio-temporal changes in the speckle structure (both the amplitude and the speckle phase). The aim of the study was to develop a method for eliminating parasitic vibrations in the scanning system, which interfere with the new OCT modalities such as angiography, relaxography, and slow process monitoring. Materials and Methods. The task of stabilizing the beam scan trajectory was successfully solved by actively filtering the controlling voltage. Results. The effect of the proposed approach application is demonstrated both on a phantom sample and examples of implementation of several modalities applied to real tissues, including: exudate visualization in vivo; OCT-angiography for visualization of microcirculation of the brain; OCT-relaxography on the example of mapping the time of mechanical relaxation of cartilage tissue; increasing the lateral resolution of OCT by compensating for defocusing. Conclusion. Vibrations of the scanning system cause artifact speckle variations that mask the informative variations of the speckles due to the relative change of the position of the scatterers inside the biological tissue caused by Brownian motion, flow, and deformation. Without proper stabilization of the scanning pattern, it is impossible to implement these modalities with quality suitable for practical use.

Among the numerous methods for improving the informative value of the optical coherence tomography (OCT), a special place is taken by the methods for increasing the spatial resolution of the resulting images. Increasing the resolution allows one to identify more clinically significant structures in OCT images and thus improve the diagnostic value of OCT. Since the transverse resolution of OCT images is determined by the physical principles different from those for the longitudinal resolution, the ways of their improvement are also different. The aim of the study is to develop a method for increasing the transverse resolution of OCT by using a finite impulse response (FIR) filter for numerical refocusing and by combining the numerically refocused images. Results. We have developed a FIR filter able to transfer the focal plane of an OCT image using the data from 17 consecutive measurements of the field scattered by the object. In addition, we propose an original method for automatic synthesis of the final OCT image with an improved transverse resolution over the entire object depth from a series of images having different focal plane positions. This will enable the OCT instrument to produce a sharply focused beam for the scanning and thus obtain images with an improved transverse resolution in the focal plane, restore the required resolution in the out-of-focus areas using numerical transfer of the focal plane, and also synthesize the final OCT image with an improved transverse resolution. The method has been tested with model objects using an OCT device operating at a central wavelength of 1 μm with the 60 nm range and a beam focused onto a spot with a diameter of 5 μm. Conclusion. The proposed method of numerically increasing the transverse resolution of OCT images allows one to obtain images with an improved transverse resolution using only a small number of OCT measurements; in the future, it will allow for creating an OCT device that produces high-resolution images in real time.