Role of scattering and birefringence in phase retardation revealed by locus of Stokes vector on Poincaré sphere

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.</p

Terahertz time-domain spectroscopy for non-invasive assessment of water content in biological samples

We apply terahertz time-domain spectroscopy for the quantitative non-invasive assessment of the water content in biological samples, such as Carpinus caroliniana tree leaves and pork muscles. The developed experimental terahertz time-domain spectroscopy system operates both in transmission and reflection modes. The Landau-Looyenga-Lifshitz-based model is used for the calculation of the water concentration within the samples. The results of the water concentration measurements are compared with the results of the gravimetric measurements. The obtained results show that the water content in biological samples can be measured non-invasively, with a high accuracy, utilizing terahertz waves in transmission and reflection modes

The use of Stokes-Mueller polarimetry for assessment of amyloid-β progression in a mouse model of Alzheimer's disease

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

Evaluating β-amyloidosis progression in Alzheimer’s disease with Mueller polarimetry

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

Imaging of early stage breast cancer with circularly polarized light

In this study, we utilize the properties of polarized light for the analysis of paraffin-embedded breast cancer samples. We perform the measurements of the full Stokes vector of back-reflected radiation and calculate the degree of polarization as a diagnostic criterion for the separation of healthy and cancer sample sections. We show that circularly polarized light scattered within the breast sample is sensitive to the presence of cancer cells. The degree of the polarization of the reected light was found to be the most sensitive parameter for the reliable differentiation of tissue

Screening of Alzheimer’s disease with multiwavelength Stokes polarimetry in a mouse model

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

Complementary analysis of Mueller-matrix images of optically anisotropic highly scattering biological tissues

Background: 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. Methods: 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. Results: 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. Conclusion: 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

Polarization and terahertz imaging for functional characterization of biological tissues

Abstract New methods for the functional characterization of biological tissues based on optical sensing and imaging techniques have been developed in recent decades. These advanced optical methods enable the quantitative scoring of tissue optical properties and give rise to the optical biopsy, which shows high potential for implementation in clinical practice in the near future. The present thesis describes the methods for the functional characterization of biological tissues based on the polarized light of the visible range and terahertz radiation. The considered approaches, enhanced by methods of mathematical and statistical analysis, were applied to differentiate various conditions of biological tissues that affect their morphological structure and water content. Polarized light imaging techniques, in particular, Stokes vector polarimetry based on circularly polarized illumination and multi-wavelength Mueller matrix imaging, were used for the label-free analysis of changes in tissue depolarization and anisotropy characteristics caused by different conditions such as cancer, beta-amyloidosis, tissue stretching, and dystrophic changes of fibrillary structures. Terahertz time-domain spectroscopy was utilized to non-invasively monitor tissue dehydration in transmission- and reflection-based measurement configurations. The fundamentals of the considered methods of optical tissue characterization, their limitations, and recent advances are overviewed. The present work aims for the improvement of the considered optical imaging and characterization techniques, as well as for discovering their potential to achieve better diagnostic efficiency and for facilitating their transfer from the laboratory to clinical use.Tiivistelmä Viime vuosikymmeninä biologisten kudosten toiminnalliseen karakterisointiin on kehitetty uusia menetelmiä, jotka perustuvat optisen tunnistamisen ja kuvantamisen tekniikoihin. Nämä kehittyneet optiset menetelmät mahdollistavat kudoksen optisten ominaisuuksien kvantitatiivisen pisteytyksen ja luovat siten pohjaa optiselle biopsialle, jolla on suuri potentiaali tulla kliiniseen käyttöön lähitulevaisuudessa. Opinnäyte kuvaa näkyvän alueen polarisoituun valoon ja terahertsisäteilyyn perustuvat biologisten kudosten toiminnallisen karakterisoinnin menetelmät. Näitä valikoituja, matemaattisilla ja tilastollisilla analyysimenetelmillä tehostettuja lähestymistapoja sovellettiin erottelemaan biologisten kudosten morfologiseen rakenteeseen ja vesipitoisuuteen vaikuttavia erilaisia olotiloja. Polarisoitua valoa hyödyntäviä kuvantamistekniikoita, erityisesti pyöröpolarisoituun valaistukseen perustuvaa Stokes-vektoripolarimetriaa ja monen aallonpituuden Mueller-matriisikuvantamista, käytettiin kudosten depolarisaatio- ja anisotropiapiirteissä tapahtuneiden erilaisten muutosten, joita aiheuttava esimerkiksi syöpä, beta-amyloidoosin, kudosvenymä ja lihasrakenteiden rappeumamuutokset, nimeämättömään analysointiin. Aikatason terahertsispektroskopiaa käytettiin kudoksen kuivumisen kajoamattomaan seurantaan mittauskokoonpanoilla, jotka perustuvat sekä läpäisyyn että heijastukseen. Työssä luodaan yleiskuva valittujen optisten kudoksen karakterisointimenetelmien perusteista, rajoitteista ja viimeaikaisesta kehityksestä. Työ tähtää näiden optisten kuvantamis- ja karakterisointitekniikoiden parantamiseen sekä niiden uuden potentiaalin löytämiseen, jotta saavutetaan parempi diagnostinen tehokkuus ja helpotetaan tekniikoiden siirtymistä laboratoriosta kliiniseen käyttöön

Assessment of water content in biological samples by terahertz time-domain spectroscopy

The noninvasive measurement of water content in biological samples utilizing the terahertz waves is a promising tool for various biomedical applications. We introduce the method of water concentration measurement in biological samples by terahertz time-domain spectroscopy.</p