Mariia Borovkova

The minimum histological criterion for the diagnostics of Alzheimer’s disease (AD) in tissue is the presence of senile plaques and neurofibrillary tangles in specific brain locations. The routine procedure of morphological analysis implies time-consuming and laborious steps including sectioning and staining of formalin-fixed paraffin-embedded (FFPE) tissue. We developed a multispectral Stokes polarimetric imaging approach that allows characterization of FFPE brain tissue samples to discern the stages of AD progression without sectioning and staining the tissue. The Stokes polarimetry approach is highly sensitive to structural alterations of brain tissue, particularly to the changes in light scattering and birefringence. We present the results of the label-free non-destructive screening of FFPE mouse brain tissue and show several polarization metrics that demonstrate statistically significant differences for tissues at different stages of AD.

We applied the wide-field Mueller imaging polarimetry for the screening of formalin-fixed paraffin-embedded samples of mouse brain tissue at different stages of brain β-amyloidosis in Alzheimer’s disease (AD). The accumulation of amyloid-beta (Aβ) deposits throughout the brain tissue is one of the key pathological hallmarks observed with the AD progression. We demonstrate that the presence of Aβ plaques influences the properties of backscattered polarized light, in particular, its degree of depolarization. By means of statistical analysis, we demonstrate that the high-order statistical moments of depolarization distributions, acquired with the multi-spectral Mueller imaging polarimetry, can be used as sensitive markers of the growing presence of Aβ plaques. The introduced label-free polarimetric approach has a potential to facilitate the current practice of the histopathology screening in terms of diagnosis accuracy, time and cost efficiency.

Significance: Biological tissues are typically characterized by high anisotropic scattering and may also exhibit linear form birefringence. Both scattering and birefringence bias the phase shift between transverse electric field components of polarized light. These phase alterations are associated with particular structural malformations in the tissue. In fact, the majority of polarization-based techniques are unable to distinguish the nature of the phase shift induced by birefringence or scattering of light. Aim: We explore the distinct contributions of scattering and birefringence in the phase retardation of circularly polarized light propagated in turbid tissue-like scattering medium. Approach: The circularly polarized light in frame of Stokes polarimetry approach is used for the screening of biotissue phantoms and chicken skin samples. The change of optical properties in chicken skin is accomplished by optical clearing, which reduces scattering, and mechanical stretch, which induces birefringence. The change of optical properties of skin tissue is confirmed by spectrophotometric measurements and second-harmonic generation imaging. Results: The contributions of scattering and birefringence in the phase retardation of circularly polarized light propagated in biological tissues are distinguished by the locus of the Stokes vector mapped on the Poincaré sphere. The phase retardation of circularly polarized light due to scattering alterations is assessed. The value of birefringence in chicken skin is estimated as 0.3 × 10 − 3, which agrees with alternative studies. The change of birefringence of skin tissue due to mechanical stretch in the order of 10 − 6 is detected. Conclusions: While the polarimetric parameters on their own do not allow distinguishing the contributions of scattering and birefringence, the resultant Stokes vector trajectory on the Poincaré sphere reveals the role of scattering and birefringence in the total phase retardation. The described approach, applied independently or in combination with Mueller polarimetry, can be beneficial for the advanced characterization of various types of malformations within biological tissues.

Breast carcinoma is the most widespread cancer among women with more than 400 000 cases diagnosed each year across EU countries. Despite the best laboratory practices, the rate of conclusive diagnosis by histological analysis for a range of cancers is only 65-75%. In fact, presently, there is no sufficiently accurate diagnostic technique providing reliable information regarding the nature of pathological formation at the stage of obtaining a biopsy material. Due to a high sensitivity of polarized light to structural variations in scattering media, the spatially resolved polarized light spectroscopy has a great potential to be used for screening malformation changes. The measurement system consists of illumination and detection channels. The light from the supercontinuum fiber laser was used in the illumination channel. The probing wavelength was selected with the acousto-optic tunable filter. The linearly polarized light from the output of the filter was then altered by a quarter-wave plate into the state of right-hand circular polarization. The state of polarization of the light diffusely reflected from the sample was collected in the measurement channel and analyzed by the Stokes polarimeter system. Automated spatial scanning of the samples was performed with the XY translation stage. The multiple measurements have been performed on a formalin-fixed, paraffin-embedded blocks of early stage breast cancer samples (ductal carcinoma in situ) and compared to the measurements from developed cancer samples (invasive ductal carcinoma). We show that circularly polarized light scattered within the breast sample is sensitive to the presence of cancer cells. The highest contrast between cancerous and normal regions was observed for the probing wavelength of 450 nm. The degree of the polarization of the reflected light was found to be the most sensitive parameter. Mapping the Stokes vectors of backscattered light on a Poincaré sphere helps to highlight the changes of polarization state.

Alzheimer’s disease, being a major societal burden, demands improvement of current techniques for its treatment and diagnostics. Currently only autopsy histology is able to provide the definite diagnosis for Alzheimer’s disease. However, the procedure is rather time consuming and costly. In the current study, we utilized Stokes and Mueller polarimetry techniques to screen for amyloid-β (Aβ) deposits in formalin-fixed, paraffin-embedded mouse brain tissue at different stages of Alzheimer’s disease. The study has shown that the presence of Aβ plaques influences the properties of scattered polarized light. The Poincaré sphere was used as a graphical tool for the visualization of the alterations of the Stokes vector, obtained with Stokes polarimetry, whereas statistical moments were used for the analysis of depolarization distributions that were acquired with Mueller polarimetry. We demonstrate the sensitivity of the last component of the Stokes vector, the degree of polarization and high-order statistical moments of depolarization to the structural alterations in brain tissue, which correspond to the disease progression. The described approach has a potential to improve the existing pathology screening methods and facilitates Aβ detection in AD research.

The interest to the use of polarized light in various modern biomedical applications is significantly growing. We explore the influence of scattering and birefringence on the phase shift between electric field components of polarized light propagated through biotissues. Degree of polarization and phase shift between the orthogonal components of circularly polarized light, propagated through the tissue samples, are examined utilizing Poincaré sphere. Scattering reduction and birefringence increase are achieved, respectively, by optical clearing and mechanical stretch. Notably different signatures of state of polarization are observed for scattering and birefringence alterations that makes it possible to distinguish mechanisms of phase retardation.

We introduce a Mueller-matrix imaging polarization-based approach for the quantitative digital screening of the polycrystalline structure of fibrillary-based biological tissues in vitro. The morphometric evaluation of histological sections of myocardium was performed utilizing the high-order statistical moments calculated based on the spatial distribution of linear and circular birefringence and dichroism obtained experimentally. We demonstrate that spatial distributions of phase of light and optical anisotropy of scattering inherent to fibrillar networks of myocardium at different necrotic stages can be effectively used as a quantitative marker of stages of myosin fibril degradation. Processing the images of phase of light scattered in biological tissues with high order statistical analysis provides a functional tool for the quantitative characterization of necrotic conditions of the myocardium.

Polarized light is widely applied in various biomedical applications in order to provide valuable information on biological tissue structure and its abnormal changes associated with different diseases. In this study, we investigate the applicability of the circularly polarized light for the diagnostics of various biotissues. This includes the investigation on the scattering and birefringence contributions in phase retardation of circularly polarized light propagated through biotissue-mimicking phantoms and skin tissue. Moreover, we present the results of the study on screening of paraffin-embedded brain samples with mice brain tissue with different stages of Alzheimer’s disease.

Using optical techniques for tissue diagnostics (so-called ‘optical biopsy’) has been a subject of extensive research for many years. Various groups have been exploring different spectral and/or imaging modalities (e.g. diffuse reflectance spectroscopy, autofluorescence, Raman spectroscopy, optical coherence tomography (OCT), polarized light microscopy, etc.) for biomedical applications. In this paper, we report on using multi-wavelength imaging Mueller polarimetry combined with an appropriated image post-processing for the detection of tissue malignancy. We investigate a possibility of complementary analysis of Mueller matrix images obtained for turbid tissue-like scattering phantoms and excised human normal and cancerous colorectal tissue samples embedded in paraffin. Combined application of correlation, fractal and statistical analysis was employed to assess quantitatively the polarization-inhomogeneous scattered fields observed at the surface of tissue samples. The combined analysis of the polarimetric images of paraffin-embedded tissue blocks has proved to be an efficient tool for the unambiguous detection of tissue malignant transformation. A fractal structure was clearly observed at spatial distributions of depolarization of light scattered in healthy tissues in a visible range of spectrum, while corresponding distributions for cancerous tissues did not show such dependence. We demonstrate that paraffin does not destroy a fractal structure of spatial distribution of depolarization. Thus, the loss of fractality in spatial distributions of depolarization for cancerous tissue is related to the structural changes in the tissue sample induced by cancer itself and, therefore, may serve as a marker of the disease. The obtained results emphasize that a combined use of statistical, correlation and fractal analysis for the Mueller-matrix image post-processing is an effective approach for an assessment of variations of optical properties in turbid tissue-like scattering media and biological tissues, with a high potential to be transferred to clinical practice for screening cancerous tissue samples.

We apply terahertz time-domain spectroscopy for the quantitative non-invasive assessment of water content in biological samples: tree leafs and pork muscles. The Landau-Looyenga-Lifshitz-based model is used for the calculation of water concentration within the samples. The obtained results show that water content in biological samples can be measured utilizing terahertz waves in transmission and reflection modes.