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It is highlighted that the current state of agricultural landscapes is characterized by a significant increase in the area of eroded arable land, which amounts to about 11 million hectares, and eroded agricultural lands — more than 13 million hectares (32.0% of their total area). Modern land-tenancy relations do not contribute to the implementation of measures to protect and increase soil fertility and have a negative effect on their fertility. In the process of using the soil cover, the needs and requirements of the ecobalance are ignored, as a result of which agricultural land is exhaustingly exploited. Soils lose a significant part of humus and such trends continue. Degradation processes are most observed in soils where agricultural techniques were violated, unfounded changes in the hydrological regime of the territory were carried out by irrigation and drainage meliorations, pollution by agrochemicals and industrial emissions occurred, which led to the removal of significant areas of productive land from active agricultural use. It has been established that the process of pollution manifests itself differently and depends on the types of harmful substances, their concentration in the soil environment and toxicity, on the natural properties and characteristics of the soil cover. It is proposed that the suitability of the soils of the contaminated lands should reflect the natural and acquired over time properties of their quality state. The combination of these properties is possible on the basis of establishing the boundaries of contaminated land on soil maps. This will make it possible to determine the area, composition of agricultural production groups and characteristics of the natural state of contaminated soils, humus content, depth of humus profiles, granulometric composition, etc. The established processes that cause various types of degradation require further processing of the parameters of indicators of crisis phenomena. It is emphasized that in the classification of processes leading to the degradation of agricultural lands, it is necessary to pay attention to the economic activity that leads to soil degradation and which is reflected in the dynamics of the structure of cultivated areas; spread of phytoviruses of different taxonomic groups in agricultural plants, weeds, wild plants and soil of different ecological regions of Ukraine; handling of waste of I–IV hazard classes.

Currently, optical biopsy technologies are being developed for rapid and label-free visualization of biological tissue with micrometer-level resolution. They can play an important role in breast-conserving surgery guidance, detection of residual cancer cells, and targeted histological analysis. For solving these problems, compression optical coherence elastography (C-OCE) demonstrated impressive results based on differences in the elasticity of different tissue constituents. However, sometimes straightforward C-OCE-based differentiation is insufficient because of the similar stiffness of certain tissue components. We present a new automated approach to the rapid morphological assessment of human breast cancer based on the combined usage of C-OCE and speckle-contrast (SC) analysis. Using the SC analysis of structural OCT images, the threshold value of the SC coefficient was established to enable the separation of areas of adipose cells from necrotic cancer cells, even if they are highly similar in elastic properties. Consequently, the boundaries of the tumor bed can be reliably identified. The joint analysis of structural and elastographic images enables automated morphological segmentation based on the characteristic ranges of stiffness (Young's modulus) and SC coefficient established for four morphological structures of breast-cancer samples from patients post neoadjuvant chemotherapy (residual cancer cells, cancer stroma, necrotic cancer cells, and mammary adipose cells). This enabled precise automated detection of residual cancer-cell zones within the tumor bed for grading cancer response to chemotherapy. The results of C-OCE/SC morphometry highly correlated with the histology-based results (r =0.96-0.98). The combined C-OCE/SC approach has the potential to be used intraoperatively for achieving clean resection margins in breast cancer surgery and for performing targeted histological analysis of samples, including the evaluation of the efficacy of cancer chemotherapy.

In this work, we use the method of optical coherence elastography (OCE) to enable quantitative, spatially resolved visualization of diffusion-associated deformations in the areas of maximum concentration gradients during diffusion of hyperosmotic substances in cartilaginous tissue and polyacrylamide gels. At high concentration gradients, alternating sign, near-surface deformations in porous moisture-saturated materials are observed in the first minutes of diffusion. For cartilage, the kinetics of osmotic deformations visualized by OCE, as well as the optical transmittance variations caused by the diffusion, were comparatively analyzed for several substances that are often used as optical clearing agents, i.e., glycerol, polypropylene, PEG-400 and iohexol, for which the effective diffusion coefficients were found to be 7.4 ± 1.8, 5.0 ± 0.8, 4.4 ± 0.8 and 4.6 ± 0.9 × 10−6 cm2/s, respectively. For the osmotically induced shrinkage amplitude, the influence of the organic alcohol concentration appears to be more significant than the influence of its molecular weight. The rate and amplitude of osmotically induced shrinkage and dilatation in polyacrylamide gels is found to clearly depend on the degree of their crosslinking. The obtained results show that observation of osmotic strains with the developed OCE technique can be applied for structural characterization of a wide range of porous materials, including biopolymers. In addition, it may be promising for revealing alterations in the diffusivity/permeability of biological tissues that are potentially associated with various diseases.

The recent impressive progress in Compression Optical Coherence Elastography (C-OCE) demonstrated diverse biomedical applications, comprising ophthalmology, oncology, etc. High resolution of C-OCE enables spatially resolved characterization of elasticity of rather thin (thickness 1 mm) samples, which previously was impossible. Besides Young's modulus, C-OCE enables obtaining of nonlinear stress-strain dependences for various tissues. Here, we report the first application of C-OCE to nondestructively characterize biomechanics of human pericardium, for which data of conventional tensile tests are very limited and controversial. C-OCE revealed pronounced differences among differently prepared pericardium samples. Ample understanding of the influence of chemo-mechanical treatment on pericardium biomechanics is very important because of rapidly growing usage of own patients' pericardium for replacement of aortic valve leaflets in cardio-surgery. The figure demonstrates differences in the tangent Young's modulus after glutaraldehyde-induced cross-linking for two pericardium samples. One sample was over-stretched during the preparation, which caused some damage to the tissue.

The use of central segmental blockades (spinal and epidural) is associated with a large number of contraindications and complications including life-threatening. The combination of general anesthesia with opioids is associated with a slow recovery of the gastrointestinal tract and other side effects of their systemic application. Therefore the search for alternative methods of pain relief in the context of Enhanced Recovery After Surgery protocols is becoming an increasingly relevant research topicn. Relative to central blocks, the fascial sheath block of peripheral nerves under ultrasound guidance is a technically simple and safe technique. This article provides a brief overview of the main blocks used for anesthesia of the anterior abdominal wall.

We report the first application of compression optical coherence elastography (C-OCE) to evaluate both linear and nonlinear elastic properties of lymph nodes (LNs) for assessing their status, which is an important factor for detecting metastasis and staging breast cancer. The reported study involved 27 excised sentinel and axillary LNs from 24 patients with breast cancer, including normal LNs (n = 6), reactive LNs with follicular hyperplasia (n = 7) and sinus histiocytosis (n = 8), and metastatic LNs (n = 6). C-OCE data were compared with co-registered gold-standard histopathology and demonstrated a significantly higher contrast in differentiation of LNs as compared to structural optical coherence tomography imaging. Normal LNs are characterized by low stiffness values in the areas of LN cortex (600 kPa). Since in terms of the tangent Young’s modulus there remained an appreciable overlap among these types of LNs, we also evaluated their elastic nonlinearity parameters. Complementary usage of both linear and nonlinear elastic parameters enabled very clear differentiation of all four main states of LNs. Thus, C-OCE imaging demonstrates high potential for future intraoperative usage to rapidly determine the LN status during breast-conserving surgery and to assess the extent of the cancer cells propagation in regional lymphatic collectors for preserving benign LNs. This is important for reducing the associated risks and complications (such as lymphedema) from excessive surgical removal of lymphoid structures.

The aims of this study are (i) to compare ultrasound strain elastography (US-SE) and compression optical coherence elastography (C-OCE) in characterization of elastically linear phantoms, (ii) to evaluate factors that can cause discrepancy between the results of the two elastographic techniques in application to real tissues, and (iii) to compare the results of US-SE and C-OCE in the differentiation of benign and malignant breast lesions. On 22 patients, we first used standard US-SE for in vivo assessment of breast cancer before and then after the lesion excision C-OCE was applied for intraoperative visualization of margins of the tumors and assessment of their type/grade using fresh lumpectomy specimens. For verification, the tumor grades and subtypes were determined histologically. We show that in comparison to US-SE, quantitative C-OCE has novel capabilities due to its ability to locally control stress applied to the tissue and obtain local stress-strain curves. For US-SE, we demonstrate examples of malignant tumors that were erroneously classified as benign and vice versa. For C-OCE, all lesions are correctly classified in agreement with the histology. The revealed discrepancies between the strain ratio given by US-SE and ratio of tangent Young’s moduli obtained for the same samples by C-OCE are explained. Overall, C-OCE enables significantly improved specificity in breast lesion differentiation and ability to precisely visualize margins of malignant tumors compared. Such results confirm high potential of C-OCE as a high-speed and accurate method for intraoperative assessment of breast tumors and detection of their margins.

We present a non-invasive (albeit contact) method based on Optical Coherence Elastography (OCE) enabling the in vivo segmentation of morphological tissue constituents, in particular, monitoring of morphological alterations during both tumor development and its response to therapies. The method uses compressional OCE to reconstruct tissue stiffness map as the first step. Then the OCE-image is divided into regions, for which the Young’s modulus (stiffness) falls in specific ranges corresponding to the morphological constituents to be discriminated. These stiffness ranges (characteristic "stiffness spectra") are initially determined by careful comparison of the "gold-standard" histological data and the OCE-based stiffness map for the corresponding tissue regions. After such pre-calibration, the results of morphological segmentation of OCE-images demonstrate a striking similarity with the histological results in terms of percentage of the segmented zones. To validate the sensitivity of the OCE-method and demonstrate its high correlation with conventional histological segmentation we present results obtained in vivo on a murine model of breast cancer in comparative experimental study of the efficacy of two antitumor chemotherapeutic drugs with different mechanisms of action. The new technique allowed in vivo monitoring and quantitative segmentation of (1) viable, (2) dystrophic, (3) necrotic tumor cells and (4) edema zones very similar to morphological segmentation of histological images. Numerous applications in other experimental/clinical areas requiring rapid, nearly real-time, quantitative assessment of tissue structure can be foreseen.

Soft biological tissues, breast cancer tissues in particular, often manifest pronounced nonlinear elasticity, i.e., strong dependence of their Young’s modulus on the applied stress. We showed that compression optical coherence elastography (C-OCE) is a promising tool enabling the evaluation of nonlinear properties in addition to the conventionally discussed Young’s modulus in order to improve diagnostic accuracy of elastographic examination of tumorous tissues. The aim of this study was to reveal and quantify variations in stiffness for various breast tissue components depending on the applied pressure. We discussed nonlinear elastic properties of different breast cancer samples excised from 50 patients during breast-conserving surgery. Significant differences were found among various subtypes of tumorous and nontumorous breast tissues in terms of the initial Young’s modulus (estimated for stress < 1 kPa) and the nonlinearity parameter determining the rate of stiffness increase with increasing stress. However, Young’s modulus alone or the nonlinearity parameter alone may be insufficient to differentiate some malignant breast tissue subtypes from benign. For instance, benign fibrous stroma and fibrous stroma with isolated individual cancer cells or small agglomerates of cancer cells do not yet exhibit significant difference in the Young’s modulus. Nevertheless, they can be clearly singled out by their nonlinearity parameter, which is the main novelty of the proposed OCE-based discrimination of various breast tissue subtypes. This ability of OCE is very important for finding a clean resection boundary. Overall, morphological segmentation of OCE images accounting for both linear and nonlinear elastic parameters strongly enhances the correspondence with the histological slices and radically improves the diagnostic possibilities of C-OCE for a reliable clinical outcome.

Fracture geometry, density, and distribution control fluid and thermal transport in low porosity rocks, as well as their seismic attributes. The creation of cracks throughout the matrix can result ...

We present a computationally highly efficient full-wave spectral model of OCT-scan formation with the following features: allowance of arbitrary phase-amplitude profile of illuminating beams; absence of paraxial approximation; utilization of broadly used approximation of ballistic scattering by discrete scatterers without limitations on their density/location and scattering strength. The model can easily incorporate the wave decay, dispersion, measurement noises with given signal-to-noise ratios and arbitrary inter-scan displacements of scatterers. We illustrate several of such abilities, including comparative simulations of OCT-scans for Bessel versus Gaussian beams, presence of arbitrary aberrations at the tissue boundary and various scatterer motions. The model flexibility and computational efficiency allow one to accurately study various properties of OCT-scans for developing new methods of their processing in various biomedical applications.

We present a real-time realization of OCT-based elastographic mapping local strains and distribution of the Young’s modulus in biological tissues, which is in high demand for biomedical usage. The described variant exploits the principle of Compression Optical Coherence Elastography (C-OCE) and uses processing of phase-sensitive OCT signals. The strain is estimated by finding local axial gradients of interframe phase variations. Instead of the popular least-squares method for finding these gradients, we use the vector approach, one of its advantages being increased computational efficiency. Here, we present a modified, especially fast variant of this approach. In contrast to conventional correlation-based methods and previously used phase-resolved methods, the described method does not use any search operations or local calculations over a sliding window. Rather, it obtains local strain maps (and then elasticity maps) using several transformations represented as matrix operations applied to entire complex-valued OCT scans. We first elucidate the difference of the proposed method from the previously used correlational and phase-resolved methods and then describe the proposed method realization in a medical OCT device, in which for real-time processing, a “typical” central processor (e.g., Intel Core i7-8850H) is sufficient. Representative examples of on-flight obtained elastographic images are given. These results open prospects for broad use of affordable OCT devices for high-resolution elastographic vitalization in numerous biomedical applications, including the use in clinic.

Linear elastic moduli of solids with similar chemical compositions usually vary fairly insignificantly. However, for a broad class of apparently similar materials, their higher-order (nonlinear) moduli may differ by many times or even by orders of magnitude. Besides their large magnitude, nonlinear effects often demonstrate qualitative/functional features inconsistent with predictions of the classical theory of nonlinear elasticity based on consideration of weak lattice (atomic) nonlinearity. The latter is mostly applicable to ideal crystals and flawless amorphous solids, whereas the presence of structural heterogeneities can drastically modify the acoustic nonlinearity of materials without appreciable variation in the linear elastic properties. Despite often rather nontrivial/nonstraightforward relationships between microstructural features of the material and the resultant “nonclassical” acoustic nonlinearity, the extremely high structural sensitivity makes utilization of nonlinear acoustic effects attractive for a broad range of diagnostic applications that have been emerging in recent years in various areas—from seismic sounding and nondestructive testing to materials characterization down to the nanoscale.

Prediction of tumour treatment response may play a crucial role in therapy selection and optimization of its delivery parameters. Here we use optical coherence angiography (OCA) as a minimally-invasive, label-free, real-time bioimaging method to visualize normal and pathological perfused vessels and monitor treatment response following vascular-targeted photodynamic therapy (PDT). Preclinical results are reported in a convenient experimental model (CT-26 colon tumour inoculated in murine ear), enabling controlled PDT and post-treatment OCA monitoring. To accurately predict long-term treatment outcome, a robust and simple microvascular metric is proposed. It is based on perfused vessels density (PVD) at t = 24 hours post PDT, calculated for both tumour and peri-tumour regions. Histological validation in the examined experimental cohort (n = 31 animals) enabled further insight into the excellent predictive power of the derived early-response OCA microvascular metric. The results underscore the key role of peri-tumour microvasculature in determining the long-term PDT response.

We present a computationally efficient full-wave spectral model of OCT-scan formation with the following capabilities/features: (i) the illuminating beam may have arbitrary phase-amplitude profile with allowance of a sharp diaphragm; (ii) paraxial approximation that limits the degree of focusing/divergence is not used; (iii) the broadly used approximation of ballistic (single) scattering by discrete scatterers is assumed without additional limitations on the density of scatterers, their distribution in space and scattering strengths with possible frequency-dependence; (iv) besides rigorous accounting for the influence of focusing/divergence of the waves, factors describing the wave decay can readily be introduced by analogy with Monte-Carlo approaches; (v) arbitrary measurement noises can easily be added to simulate required signal-to-noise ratios. The model also allows one to account for arbitrary (e.g., random or flow/deformation-induced) displacements of scatterers between subsequently generated scans. Thus, in view of the above-listed features the model can be characterized as comprehensive in the framework of ballistic scattering by discrete scatterers. The model is computationally efficient due to the use of only rapid summations and fast Fourier transforms. Main model features are illustrated, including simulations of OCT scans for a nearly non-diverging Bessel beam and a focused Gaussian beam, with the possibility to introduce at the tissue boundary arbitrary aberrations represented via Zernike polynomials often utilized for describing aberrations in ophthalmology. The unprecedented flexibility and high computational efficacy of the model open a broad range of possibilities for studying OCT-scan properties and developing new methods of their processing for biomedical diagnostics.

Laser-assisted relaxation of internal stresses can be used to stabilize the new shape of cartilaginous implants. The ability of cartilage tissue to experience irreversible deformation under certain conditions, as well as to restore its original configuration after external mechanical stress, is studied in near real time using a new method of optical coherent elastography (OCE), developed to visualize slow deformation. The OCE technique allows one to monitor the efficiency of laser-induced stress relaxation at 1–2 minute intervals using 2D subsurface strain mapping. It has been shown that the redistribution of the interstitial fluid due to the applied load is an important factor for the mechanism of "shape memory" of the cartilage. Deviations in the behavior of cartilage from the usual elastic properties of homogeneous materials, such as subsurface dilatation opposing the applied load, are identified and analyzed.

This report presents an overview of recent progress in the development of novel OCE-based technologies enabling non-invasive morphological segmentation of tumor tissues during their natural development and response to therapies. The approach is based on preliminary quantitative assessment of characteristic elasticity ranges corresponding to the segmented morphological constituents (“quasistatic elasto-spectroscopy”). It has been found that such constituents are characterized by fairly well separated ranges of the Young’s modulus, which makes it possible to automatically segment up to 4-6 such zones in OCE-based elasticity maps. High consistency of such OCE-based procedure with conventional morphological segmentation of histological slides in terms of percentages of the segmented-zone areas has been demonstrated. Unlike invasive, time-consuming and laborious histological studies the developed OCE-based segmentation is non-invasive and can be performed even in vivo. High accuracy and sensitivity of the OCE-based-segmentation was demonstrated in vivo for two different types of model tumors (4T1 and Ct26) treated by PDT and chemotherapies. The OCE-based analysis can readily be combined with such OCT-based extensions as texture analysis and OCT-based angiography. The latter opens the possibility to combine morphological assessment with functional characterization of tumor response to therapies. OCE-based characterization of mechanical heterogeneity and elasticity spectra of tumors has also proven to be efficient for express assessment of patients’ breast-cancer subtypes. Overall, the developed OCE-based assessment in many applications suggests a rapid and in vivo feasible alternative to conventional histology and can be efficiently used in a wide range of biomedical problems.

An important factor in assessing tumor status for determining therapeutic and surgical tactics is the study of its morphological structure. In particular, preoperative differentiation/grading of colorectal adenocarcinomas is very important for the adjustment of neoadjuvant therapy, surgical technique choice and survival prediction. To achieve the maximum benefit and to avoid unnecessary side effects, the ability to distinguish high-grade from low-grade colorectal adenocarcinoma, as well as identification of patients with high recurrence risk before the possible initiation of treatment will increase the quality and duration of patients' life. Taking into account the peculiarities of the biology of intestinal cancer, optical coherence elastography, as a method of studying tissue structure at a shallow depth, may be promising in the study of colorectal adenocarcinoma. Possibilities of optical coherence elastography in differentiating low-grade and high-grade types of colorectal adenocarcinoma are demonstrated in this study. The reported results are based on revealed qualitative criteria for assessment of OCE images in combination with quantitative statistically significant differences in characteristic stiffness values for low-grade and high-grade colorectal adenocarcinomas.

An understanding of micro- and macrofracture behavior in low porosity rocks is pertinent to several areas of energy and environmental science such as petroleum production, carbon sequestration, and enhancement of technologies based on geothermal energy, etc. For example, the carbonate reservoirs in dolomitic or micritic formations with matrix porosities below 6% suggest the importance of fracture-augmented permeability in production. Similarly, hydrocarbons have been found on nearly every continent in tight basement rocks, all of which have little matrix porosity and their permeability therefore rely solely on hydraulic connectivity from fractures. For geothermal energy, various igneous and sedimentary rocks (granites, basalts, and limestones) are being exploited across the globe, with some of the lowest porosity and permeability. In all these cases, fractures are necessary to improve rock permeability and thermal exchange between the rock and working fluid, which can be enabled by hydraulic stimulation, as well as by secondary cracking due to extreme temperature gradients from the injection of cold water. The fracture geometry, density, and distribution all together control not only fluid and thermal transport in the rocks, but also their seismic attributes that can be used to extract information about the fractures. In order to accurately interpret the seismo-acoustic data (usually, the velocities of compression and shear waves) reliable rock physics models are required. Here, we report the results of interpretation of such experimental data for both as-cored rock samples and those subjected to thermo-hydro-chemo-mechanical damage (THCMD) in the laboratory. For interpretation, we use a convenient model of fractured rock in which fractures are represented as planar defects with decoupled shear and normal compliances. The application of such an approach makes it possible to assess and compare the elastic properties of fractures in the rocks before and after application of THCMD procedures. For the analyzed samples of granites, basalts, and limestones it has been found that for a significant portion of rocks, the ratio of normal-to-shear compliances of cracks significantly differ from the value typical of conventionally assumed penny-shape cracks. Furthermore, for some samples, this ratio appears to be noticeably different for fractures existing in the as-cored rock and arising in the same rock after THCMD procedures. These results indicate that damage to a rock typically changes its compliance ratio since the old and new cracks are likely to have different elastic properties. Our results are also consistent with the notion that a specific damage process occurring for a given microstructure will consistently create cracks with a particular set of elastic properties. The proposed methodology for assessment of elastic properties of cracks in rock samples subjected to thermo-hydro-chemo-mechanical damage has given previously inaccessible useful information about the elastic properties of fractures and can be extended to interpretation of seismic attributes of rocks for a broad range of other applications.

We present a novel method, which by analogy with the term "mass-spectroscopy" can be called "quasistatic elasto-spectoscopy" based on quantitative compressional Optical Coherence Elastogrphy (C-OCE). The method relies on initial determining of characteristic stiffness ranges for various morphological components of the tissue by comparing the OCE-based stiffness maps and histology. Such pre-calibration allows one to perform morphological segmentation of OCE-images demonstrating excellent correlation with segmentation of conventional histological images, but can be performed using freshly-extracted samples and even in vivo.

We present a robust semi-analytical multi-factor model of OCT-scan formation with rigorous accounting for the beam-focusing effects. It is based on numerical summation of the contributions of the localized sub-resolution scatterers, accounting for variations in the phase-amplitude parameters of the incident and backscattered optical waves, with a subsequent integration of the latter over the objective aperture. The main advantage of presented model is its convenience to account for scatterer motions in comparison with classical Monte-Carlo OCT-simulation approaches. In view of difficulties in performing highly-controlled phantom experiments, application of an adequate numerical model opens very flexible and convenient possibilities for evaluating the influence of scatter motions using numerically simulated OCT scans. The numerical model readily allows one to introduce various (e.g., regular/irregular or mixed) types of scatterer motions.

This report presents a clinical case of a 57-year-old female patient who was admitted for dyspnea, productive cough, reduced left ventricular (LV) systolic function, and who had previously undergone thoracocentesis for significant pleural effusion. This case is a unique combination of lymphocytic myocarditis and massive intracardiac and ileo-caval thrombosis. Morphological verification of the diagnosis, that was necessary prior to the administration of immunosuppressive therapy due to the prothrombogenic effect of glucocorticoids, provided a justification for a basis therapy for myocarditis, which significantly improved the patient’s condition.

The possibility to assess molecular-biological and morphological features of particular breast cancer types can improve the precision of resection margin detection and enable accurate determining of the tumor aggressiveness, which is important for treatment selection. To enable reliable differentiation of breast-cancer subtypes and evaluation of resection margin, without performing conventional histological procedures, here we apply cross-polarization optical coherence tomography (CP-OCT) and compare it with a novel variant of compressional optical coherence elastography (C-OCE) in terms of the diagnostic accuracy (Ac) with histological verification. The study used 70 excised breast cancer specimens with different morphological structure and molecular status (Luminal A, Luminal B, Her2/Neo+, non-luminal and triple-negative cancer). Our first aim was to formulate convenient criteria of visual assessment of CP-OCT and C-OCE images intended (i) to differentiate tumorous and non-tumorous tissues and (ii) to enable more precise differentiation among different malignant states. We identified such criteria based on the presence of heterogeneities and characteristics of signal attenuation in CP-OCT images, as well as the presence of inclusions/mosaic structures combined with visually feasible assessment of several stiffness grades in C-OCE images. Secondly, we performed a blinded reader study of the Ac of C-OCE versus CP-OCT, for delineation of tumorous versus non-tumorous tissues followed by identification of breast cancer subtypes. For tumor detection, C-OCE showed higher specificity than CP-OCT (97.5% versus 93.3%) and higher Ac (96.0 versus 92.4%). For the first time, the Ac of C-OCE and CP-OCT were evaluated for differentiation between non-invasive and invasive breast cancer (90.4% and 82.5%, respectively). Furthermore, for invasive cancers, the difference between invasive but low-aggressive and highly-aggressive subtypes can be detected. For differentiation between non-tumorous tissue and low-aggressive breast-cancer subtypes, Ac was 95.7% for C-OCE and 88.1% for CP-OCT. For differentiation between non-tumorous tissue and highly-aggressive breast cancers, Ac was found to be 98.3% for C-OCE and 97.2% for CP-OCT. In all cases C-OCE showed better diagnostic parameters independently of the tumor type. These findings confirm the high potential of OCT-based examinations for rapid and accurate diagnostics during breast conservation surgery.

Quantitative mapping of deformation and elasticity in optical coherence tomography has attracted much attention of researchers during the last two decades. However, despite intense effort it took ~15 years to demonstrate optical coherence elastography (OCE) as a practically useful technique. Similarly to medical ultrasound, where elastography was first realized using the quasi-static compression principle and later shear-wave-based systems were developed, in OCE these two approaches also developed in parallel. However, although the compression OCE (C-OCE) was proposed historically earlier in the seminal paper by J. Schmitt in 1998, breakthroughs in quantitative mapping of genuine local strains and the Young's modulus in C-OCE have been reported only recently and have not yet obtained sufficient attention in reviews. In this overview, we focus on underlying principles of C-OCE; discuss various practical challenges in its realization and present examples of biomedical applications of C-OCE. The figure demonstrates OCE-visualization of complex transient strains in a corneal sample heated by an infrared laser beam.

As was shown earlier in the animal experiments, compression optical coherence elastography (OCE) is a highly sensitive method for studying the morphological features of biological tissues. An attempt was made to study the possibilities of the OCE method for identifying and differentiating from each other various morphological structures in human tissues. Postoperative samples of human breast cancer and human colon cancer were studied. Histological examination identified areas of morphological structures - (I) adipose tissue, (II) stroma and (III) tumor tissue in breast cancer samples; and areas of (I) mucous membrane and (II) tumor tissue in colon cancer samples. For these areas, an accurate comparison was made with OCE images and stiffness ranges for morphological structures were obtained. This observation allows us to make a conclusion that OСE can be a promising method for studying the structure of human tissue in clinics.

We report a new application of compressional optical coherence elastography (OCE) to discriminate morphological constituents of biological tissues by analyzing OCE images obtained either in vivo or for freshly excised samples. The new technique enables quantitative morphological segmentation of OCE images with delineation of several (~4-6) tissue constituents. As the first step, the method uses compressional OCE to reconstruct stiffness maps for a pre-chosen standardized pressure over the entire area of the OCE image. Then specific stiffness ranges (characteristic "stiffness spectra") are initially determined by careful comparison of the OCE-based stiffness maps with the results of segmentation of "gold-standard" histological slices. After such pre-calibration, the stiffness maps can be automatically segmented into regions, for which the Young’s modulus (stiffness) falls in specific ranges corresponding to the morphological constituents to be discriminated. The results of such automated segmentation of OCE-images demonstrate a striking correlation with the results of conventional segmentation of histological slices in terms of percentages of the segmented zones. High sensitivity of the OCE-method to histological alterations was demonstrated in vivo in comparative studies of various types of anti-tumor therapies using murine tumor models. Studies of >100 samples of freshly excised breast cancer samples revealed strong correlation between the tumor-tissue subtype and its morphological composition determined by the developed OCE method. Thus, the developed approach can be used as a basis for express OCE-based biopsy (feasible intraoperatively). Longitudinal in vivo monitoring of morphological alterations in tumors under therapy or during natural development is also possible for locations accessible to OCT.