Optical coherence elastography for non-invasive monitoring of tumor elasticity under chemotherapy: Pilot study

Abstract

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.