No abstract

Pronounced elastic nonlinearity intrinsic to many biological tissues makes the Young's modulus (stiffness) of the tissue strongly dependent on the current strain and stress. The measured modulus may vary several times for rather moderate tissue straining within a few per cent, such strains being quite typical for compressional optical coherence elastography (C-OCE). This pronounced stiffness variability may strongly affect diagnostic conclusions based on the stiffness measurements, so that obtaining reproducible estimates of stiffness in C-OCE is an important and challenging problem. Here, we report a novel full-optical method allowing one to ensure a preselected stress level in C-OCE stiffness mapping. The proposed improved OCE visualization enables reproducible quantitative elastographic visualization even for strongly elastically-nonlinear biological tissues, which is of key importance for reliability of diagnostic applications of C-OCE. In particular, in oncology such OCE technique can be used to control clear tumor resection boundary, express assessment of tumor subtypes and in vivo monitoring of morphological alterations in animal tumor models in response to anti-tumor therapies.

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.

Emerging methods of anti-tumor therapies require new approaches to tumor response evaluation, especially enabling label-free diagnostics and in vivo utilization. Here, to assess the tumor early reaction and predict its long-term response, for the first time we apply in combination the recently developed OCT extensions-optical coherence angiography (OCA) and compressional optical coherence elastography (OCE), thus enabling complementary functional/microstructural tumor characterization. We study two vascular-targeted therapies of different types, (1) antiangiogenic chemotherapy (ChT) and (2) photodynamic therapy (PDT), aimed to indirectly kill tumor cells through blood supply injury. Despite different mechanisms of anti-angiogenic action for ChT and PDT, in both cases OCA demonstrated high sensitivity to blood perfusion cessation. The new method of OCE-based morphological segmentation revealed very similar histological structure alterations. The OCE results showed high correlation with conventional histology in evaluating percentages of necrotic and viable tumor zones. Such possibilities make OCE an attractive tool enabling previously inaccessible in vivo monitoring of individual tumor response to therapies without taking multiple biopsies.

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.

No abstract

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.

Tumor cells are well adapted to grow in conditions of variable oxygen supply and hypoxia by switching between different metabolic pathways. However, the regulatory effect of oxygen on metabolism and its contribution to the metabolic heterogeneity of tumors have not been fully explored. In this study, we develop a methodology for the simultaneous analysis of cellular metabolic status, using the fluorescence lifetime imaging microscopy (FLIM) of metabolic cofactor NAD(P)H, and oxygen level, using the phosphorescence lifetime imaging (PLIM) of a new polymeric Ir(III)-based sensor (PIr3) in tumors in vivo. The sensor, derived from a polynorbornene and cyclometalated iridium(III) complex, exhibits the oxygen-dependent quenching of phosphorescence with a 40% longer lifetime in degassed compared to aerated solutions. In vitro, hypoxia resulted in a correlative increase in PIr3 phosphorescence lifetime and free (glycolytic) NAD(P)H fraction in cells. In vivo, mouse tumors demonstrated a high degree of cellular-level heterogeneity of both metabolic and oxygen states, and a lower dependence of metabolism on oxygen than cells in vitro. The small tumors were hypoxic, while the advanced tumors contained areas of normoxia and hypoxia, which was consistent with the pimonidazole assay and angiographic imaging. Dual FLIM/PLIM metabolic/oxygen imaging will be valuable in preclinical investigations into the effects of hypoxia on metabolic aspects of tumor progression and treatment response.