In this work, we propose using spectro-polarimetric imaging to monitor tumors growth of non-pigmented intra-dermal grafted tumors on murine models. We use for this purpose a full Mueller imaging polarimeter operating in the near infrared range. The injection site was imaged twice a week with our system from day 1 to the sacrifice of the mice while, in parallel, tumor volume was evaluated using standard caliper measurements. 40 nude mice were injected with a nonpigmented cancerous cell line (MDA) to produce intra-dermal tumors and separated into three different groups. The first group, called “early”, received a Docetaxel treatment as soon as the polarization signal detected a change in the tissue matrix, the second one received the Docetaxel treatment as soon as the tumor reached an estimated volume of 20 mm3 and the last group, was used as a control group. We demonstrate that early detection of tumor development based on depolarization metrics permits to control the tumor growth. We show also that while the tumor grows the depolarization contrast decreases while spectral contrasts appear. We observe also a change in fiber orientation around the tumor at the necrotic stage. This is highlighted by the azimuthal retardance orientation extracted from the polar decomposition of the Mueller matrix. This study confirms the usefulness of polarimetric contrast for tumor detection and monitoring. In the future, a precise characterization of different stages of tumor development could be useful for drug efficiency assessment in small-animal studies or in clinical applications.
When a light wave passes through a sample, it undergoes a phase delay related to the optical path it has taken. The amount of shift is proportional to the product of the refractive index and the thickness of the sample and cannot be measured using conventional light microscopy. Furthermore, the velocity of light propagation in an optically anisotropic medium may depend on its polarization state. This causes a phase shift between the polarization components of the oscillating electric field called retardance. Both quantitative phase and polarimetric retardance are commonly used to examine biological tissues. This work investigates the complementarity of information retrieved by two optical modalities: Fourier Ptychographic Microscopy and Mueller Matrix Microscopy. We present two constructed microscopes and then compare the results obtained using histological slides for experimental validation.
Imaging spectropolarimetry is an informative technique that can be useful as a tool to detect and analyze cancerous tissues. However, to fit clinical standards, imaging spectropolarimeters must be fast, drift-free, and without any recurrent calibration, which is not the case for most imaging spectropolarimeters based on nematic liquid crystal phase modulators. Here, we present an instrument based on a novel architecture of differential liquid crystal variable retarders cells. A complete spectropolarimeter was built using this architecture and is now part of a clinical study at the dermatology department of the Strasbourg University Hospital.
Mueller polarimetry is a powerful characterization technique for a variety of samples and a promising optical-biopsy tool for early detection of cancer. Recent advances in Mueller imaging devices allow the collection of large ex-vivo and invivo image databases. Although the technique is sensitive to subtle changes in the micro-organization of tissue, the Mueller matrices of such complex media contain intertwined polarimetric effects and are difficult to interpret. To identify the polarimetric signature of a given tissue modification (cancerous or not), machine learning tools are particularly well suited. However, a statistically sound approach is needed to make the most out of these tools and avoid common pitfalls. We present a global statistical framework based on decision theory. It consists of a complete preprocessing and analysis pipeline for polarimetric bioimages. In the analysis stage, we use a loss-risk-based approach to automatically select the optimal classifier among a library of classifiers. The approach allows to determine the subset of polarimetric parameters of interest, to determine the parameters of the classifiers and to assess classifier performance using cross-validation. The proposed framework is illustrated with precancer detection on human ex-vivo cervical samples.
The process of tumor growth is a phenomenon which, if understood better, could greatly improve the diagnostic and treatment of patients. In this context, the use of polarimetric imaging can offer more information than classical imaging methods. Here we use a new kind of calibration-free spectro-polarimeter which can be helpful for optical biopsy. Fifty different mice have been studied in full Mueller polarimetry with this device. Some were injected with very pigmented melanoma cells, others with non-pigmented breast cancer cells. Variations in depolarization were measured throughout this study: melanomas were accompanied with intense drops in depolarization, while mice injected with breast cancer cells showed a more diffuse decrease in depolarization. The study confirmed the potential of polarimetric imaging as an optical biopsy tool.