Collagen is the major component of the extracellular matrix in mammals and its characteristics provide important information about the state of connective tissue. There are only few methods of label-free visualization of collagen fibers; the most frequently used is the second harmonic generation (SHG) microscopy. SHG microscopy is a non-invasive technique for the assessment of the abundance and structure of fibrillar collagen with a high resolution and specificity. At constant measurement parameters (magnification, excitation power, resolution, digital gain of registration matrix), quantitative analysis of SHG images provides a reliable characterization of collagen state. Current approaches to the SHG signal quantification are numerous and typically should be adapted to a specific task. In this review, we systematize the variety of these approaches and present the examples of biomedical application of the SHG signal quantitative analysis, as well of combined application of SHG and autofluorescence imaging.

We report realizations of OCT combining conventional structural imaging, polarization-sensitive one, as well as allowing for real-time angiographic, elastographic and lymphangiographic modalities with manual-operation capabilities. Among the main features of the developed device one can point out on-flight imaging of microvascular network with feedback for clinicians when performing angiography; in elastography - robust "vector" method of interframe phasevariation gradient estimation and stiffness quantification using reference silicone layers; lymphangiography utilizing pixel statistics beyond conventional amplitude thresholding, etc. These capabilities are ensured by the developed optical schemes of the probe, signal receiving parts, as well as computationally efficient signal processing methods. Examples of the developed device usage in preclinical and clinical applications are discussed (efficient criteria for PDT success; angiographic monitoring of complications during radiotherapy; elastographic classification of tumor and non-tumor regions; detailed imaging of fairly rapid transient and slowly varying deformations in laser-assisted reshaping of collagenous tissues; lymphangiography-based diagnostics in gynecology; otolaryngologic applications for diagnosing inner ear diseases, etc.)

The aim of the investigation was evaluating the possibilities of cross-polarization optical coherence tomography (CP OCT) to monitor the effectiveness of photodynamic therapy (PDT) and radiation therapy (RT) of the oral cancer and of the cervical cancer. Materials and Methods. The CP OCT investigation was performed by an OCT-1300U tomograph (Institute of Applied Physics of the Russian Academy of Sciences, LLC “Biomedtech”, Russia). The monitoring of the two types of treatment was performed after different periods of exposure: for RT of the oral cancer — once for every 2–3 days throughout the whole course of the treatment, starting from the first day of radiation; for the PDT of the cancers of the skin and cervix uteri — before the exposure, immediately after the exposure, and then at 1 day, 7 day and 1 month after the exposure. Fourteen patients were examined in total. Results. The results of the study of the medical pathomorphism of different kinds of tumors performed on the 14 patients showed that visual evaluation of CP OCT images of a tumor does not reveal any visible changes in response to RT, however it does register the reaction of the normal mucosa in the area exposed to the radiation. During the PDT of tumors of the skin and cervix mucosa CP OCT was capable of detecting the key morphological changes (edema, necrosis, and structural recovery). It can be applied most effectively at later stages of the follow-up observation (at 30–35 days after PDT) to evaluate the completeness of the recovery of the stromal component of the tissues. Conclusion. The use of CP OCT contributes to realization of non-invasive monitoring of the responses of tumors and the adjacent normal tissues to PDT and to RT that can be useful for evaluation of the effectiveness of therapy and to help in choosing optimal tactics for the treatment.

The aim of the investigation was to determine the optimal dates and morphological parameters of inoculated CT-26 tumors for evaluating the effectiveness of anti-cancer therapy. This was undertaken on the basis of morphological and morphometric investigations of the tumor growth dynamics by identifying the daily structural changes which were occurring. Materials and Methods. The features of morphological changes in experimental tumors growth were evaluated on Balb/c mice using the mouse colon CT-26 adenocarcinoma inoculated onto the external side of mouse ear auricles (n=20). The inoculation dose in all cases was 2·105 cells. The animals were removed by cervical dislocation on days 4, 8, 11, 17–19 or 20–22 after the inoculation. Each group consisted of four animals. The excised tumor was exposed to macroscopic and histological investigation. The specimens were stained by hematoxylin and eosin and picro-fuchsin using the Van-Gieson method. There were examined the quantitative composition of the cells the areas of the stroma and tumor parenchyma, the volume of the vascular bed, the area of necrosis and the presence of hemodynamic disruptions, the mitotic activity of the tumor cells. Results. The study of the features of morphological changes in experimental tumors growth showed that tumor growth is determined not only by the mitotic activity of the cells, but also by the degree of the vascular bed development and its capacity for performing its required functional load to the full. It was found that tumor angiogenesis is a fluctuating process which is, to a certain degree, connected with the state of the tumor cells. The formation of the vascular bed in the form of sinusoidal capillaries begins on day 4 after inoculation and it increases continuously until day 11. Between days 17–19 after inoculation there is a decrease in the proportion of vessels in the tumor tissue, but by days 20–22 this has increased again with the formation not only of sinusoidal capillaries, but also of vessels of larger diameters (to 200 μm). The manifestations of spontaneous tumor regration are characterized by the occurrence of cells with irreversible damage to their nuclei and cytoplasm with a parallel decrease in their mitotic activity, and by the appearance of mosaically located areas of spontaneous necrosis. Spontaneous regression is also reflected in the observation of hemodynamic and hemorheologic disorders — plethora (hyperemia), stasis, the sludge-phenomenon and diapedetic hemorrhage. Here there is a connection between the severity of the changes associated with spontaneous regression and the relationship of the tumor volume to the degree of the vascular bed development. When the tumor is small and the vascular network is well-developed, as is seen on day 11, spontaneous regression is revealed only by irreversible cell changes in a small number of tumor cells, while, by contrast, the bigger tumor size with a small number of vessels, as is registered on days 17–19, is characterized by a considerably greater number of dead cells (85%). The tumors of larger sizes observed on days 20–22 after inoculation, despite their more developed network of blood vessels, are characterized by a high level of spontaneous regression, which leads us to the conclusion that there is a mismatch between the level of angiogenesis in relation to the needs of the proliferating parenchymal elements. Conclusion. The development of this carcinoma is characterized by two parallel processes: the formation of the tumor as a morphological substrate and the development of spontaneous regressive changes within it. The state of the tumor cells and the degree of development of spontaneous regressive changes depend on both the size of the tumor and on the level of development and functioning of the vascular network. These findings suggest that when using CT-26 tumors inoculated into mouse ears for evaluating the effectiveness of anti-cancer therapy periods of greater than 11 days should be avoided, as from this time there are evident manifestations of spontaneous pathomorphism in the tumor.