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

Influence of scattering and birefringence on the phase shift between electric field components of polarized light propagated through biological tissues

Abstract 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 retardatio

Towards non-invasive reflection measurement of water content in biotissue by means of terahertz timedomain spectroscopy

Abstract 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

Gastrointestinal cancer diagnostics by terahertz time domain spectroscopy

Abstract Samples of fresh excised tissues obtained from patients who had undergone gastric cancer have been investigated. Samples consisted of cancer zone, normal zone and pathologically changed zone. Their optical properties and spectral features were investigated by terahertz time-domain spectroscopy (THz-TDS) in reflection mode. It was found that waveforms of reflected signals from normal and cancer tissues and their optical properties were well distinguished, so it can be concluded that it is possible to discriminate gastric cancer tissue from normal by using THz-TDS

Assessment of the Alzheimer progression with multiwavelength stokes polarimetry

Abstract Multiwavelength Stokes polarimetry imaging is used for screening fixed bulk mouse brain tissue blocks at different stages of Alzheimer’s disease, providing statistically significant difference sufficient for quantitative analysis of brain tissue

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

Abstract 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

Investigation of terahertz radiation influence on rat glial cells

Abstract We studied an influence of continuous terahertz (THz) radiation (0.12–0.18 THz, average power density of 3.2 mW/cm²) on a rat glial cell line. A dose-dependent cytotoxic effect of THz radiation is demonstrated. After 1 minute of THz radiation exposure a relative number of apoptotic cells increased in 1.5 times, after 3 minutes it doubled. This result confirms the concept of biological hazard of intense THz radiation. Diagnostic applications of THz radiation can be restricted by the radiation power density and exposure time