E. Du

Characterizing the microstructures of biological tissues using Mueller matrix and transformed polarization parameters

Mueller matrices can be used as a powerful tool to probe qualitatively the microstructures of biological tissues. Certain transformation processes can provide new sets of parameters which are functions of the Mueller matrix elements but represent more explicitly the characteristic features of the sample. In this paper, we take the backscattering Mueller matrices of a group of tissues with distinctive structural properties. Using both experiments and Monte Carlo simulations, we demonstrate qualitatively the characteristic features of Mueller matrices corresponding to different structural and optical properties. We also calculate two sets of transformed polarization parameters using the Mueller matrix transformation (MMT) and Mueller matrix polar decomposition (MMPD) techniques. We demonstrate that the new parameters can separate the effects due to sample orientation and present quantitatively certain characteristic features of these tissues. Finally, we apply the transformed polarization parameters to the unstained human cervix cancerous tissues. Preliminary results show that the transformed polarization parameters can provide characteristic information to distinguish the cancerous and healthy tissues.

Mueller matrix polarimetry for differentiating characteristic features of cancerous tissues

Abstract. Polarization measurements allow one to enhance the imaging contrast of superficial tissues and obtain new polarization sensitive parameters for better descriptions of the micro- and macro- structural and optical properties of complex tissues. Since the majority of cancers originate in the epithelial layer, probing the morphological and pathological changes in the superficial tissues using an expended parameter set with improved contrast will assist in early clinical detection of cancers. We carry out Mueller matrix imaging on different cancerous tissues to look for cancer specific features. Using proper scattering models and Monte Carlo simulations, we examine the relationship between the microstructures of the samples, which are represented by the parameters of the scattering model and the characteristic features of the Mueller matrix. This study gives new clues on the contrast mechanisms of polarization sensitive measurements for different cancers and may provide new diagnostic techniques for clinical applications.

A possible quantitative Mueller matrix transformation technique for anisotropic scattering media/Eine mögliche quantitative Müller-Matrix-Transformations-Technik für anisotrope streuende Medien

Abstract By conducting both the experiments on samples containing well-aligned fibers and Monte Carlo simulations based on the sphere cylinder scattering model (SCSM), we present a Mueller matrix transformation (MMT) method for quantitatively characterizing the properties of anisotropic scattering media. We obtained a set of parameters by fitting the Mueller matrix elements to trigonometric curves in polar coordinates. These new parameters can be expressed as analytical functions of the Mueller matrix elements and display simple relationships to the structural and optical properties of the anisotropic scattering media, such as the anisotropy, the direction of the fibers, and the sizes of the scatterers. Experimental results on biological tissues show that these new parameters can be used in biomedical research. However, further studies are still necessary to correlate the MMT parameters to pathological features. Zusammenfassung Mit der Durchführung von Experimenten an Proben mit gut ausgerichteten Fasern sowie von Monte-Carlo-Simulationen basierend auf dem Kugel-Zylinder-Streumodell (sphere cylinder scattering model, SCSM) wird eine Müller-Matrix-Transformations (MMT)-Methode zur quantitativen Charakterisierung der Eigenschaften von anisotropen Streumedien vorgestellt. Durch die Anpassung („Fit“) der Müller-Matrix-Elemente an trigonometrische Kurven in Polarkoordinaten erhält man eine Vielzahl von Parametern. Diese neuen Parameter können als analytische Funktion der Müller-Matrix-Elemente ausgedrückt werden und zeigen einfache Beziehungen zu den strukturellen und optischen Eigenschaften des anisotropen Streumediums, wie z.B. der Anisotropie, der Richtung der Fasern und der Größe der Streuer. Experimentelle Ergebnisse an biologischen Geweben zeigen, dass diese neuen Parameter in der biomedizinischen Forschung verwendet werden können. Dennoch sind weitere Studien notwendig, um die MMT-Parameter mit pathologischen Merkmalen zu korrelieren.

Two-dimensional backscattering Mueller matrix of sphere-cylinder birefringence media

Abstract. We have developed a sphere–cylinder birefringence model (SCBM) for anisotropic media. The new model is based on a previously published sphere–cylinder scattering model (SCSM), but the spherical and cylindrical scatterers are embedded in a linearly birefringent medium. A Monte Carlo simulation program for SCBM was also developed by adding a new module to the SCSM program to take into account the effects of birefringence. Simulations of the backscattering Mueller matrix demonstrate that SCBM results in better agreement with experimental results than SCSM and is more suitable to characterize fibrous tissues such as skeletal muscle. Using Monte Carlo simulations, we also examined the characteristics of two-dimensional backscattering Mueller matrix of SCBM and analyzed the influence of linear birefringence.

Mapping local orientation of aligned fibrous scatterers for cancerous tissues using backscattering Mueller matrix imaging

Abstract. Polarization measurements are sensitive to the microstructure of tissues and can be used to detect pathological changes. Many tissues contain anisotropic fibrous structures. We obtain the local orientation of aligned fibrous scatterers using different groups of the backscattering Mueller matrix elements. Experiments on concentrically well-aligned silk fibers and unstained human papillary thyroid carcinoma tissues show that the m22, m33, m23, and m32 elements have better contrast but higher degeneracy for the extraction of orientation angles. The m12 and m13 elements show lower contrast, but allow us to determine the orientation angle for the fibrous scatterers along all directions. Moreover, Monte Carlo simulations based on the sphere-cylinder scattering model indicate that the oblique incidence of the illumination beam introduces some errors in the orientation angles obtained by both methods. Mapping the local orientation of anisotropic tissues may not only provide information on pathological changes, but can also give new leads to reduce the orientation dependence of polarization measurements.

Probing microstructural information of anisotropic scattering media using rotation-independent polarization parameters

Polarization parameters contain rich information on the micro- and macro-structure of scattering media. However, many of these parameters are sensitive to the spatial orientation of anisotropic media, and may not effectively reveal the microstructural information. In this paper, we take polarization images of different textile samples at different azimuth angles. The results demonstrate that the rotation insensitive polarization parameters from rotating linear polarization imaging and Mueller matrix transformation methods can be used to distinguish the characteristic features of different textile samples. Further examinations using both experiments and Monte Carlo simulations reveal that the residue rotation dependence in these polarization parameters is due to the oblique incidence illumination. This study shows that such rotation independent parameters are potentially capable of quantitatively classifying anisotropic samples, such as textiles or biological tissues.

Two-dimensional and surface backscattering Mueller matrices of anisotropic sphere-cylinder scattering media: a quantitative study of influence from fibrous scatterers

Abstract. We present both the two-dimensional backscattering point-illumination and surface-illumination Mueller matrices for the anisotropic sphere-cylinder scattering media. The experimental results of the microsphere-silk sample show that the Mueller matrix elements of an anisotropic scattering medium are different from those of an isotropic medium. Moreover, both the experiments and Monte Carlo simulations show that the directions of the fibrous scatterers have prominent effects on the Mueller matrix elements. As the fibrous samples rotate, the surface-illumination Mueller matrix measurement results for the m12, m21, m13, m31, m22, m23, m32, and m33 elements represent periodical variations. Experiments on skeletal muscle and porcine liver tissue samples confirm that the periodical changes for the surface-illumination Mueller matrix elements are closely related to the well aligned fibrous scatterers. The m22, m23, m32, and m33 elements are powerful tools for quantitative characterization of anisotropic scattering media, including biological tissues.

A study on forward scattering Mueller matrix decomposition in anisotropic medium

In this work, we apply Mueller matrix polar decomposition (MMPD) method in a forward scattering configuration on anisotropic scattering samples and look for the physics origin of depolarization and retardance. Using Monte Carlo simulations on the sphere-cylinder birefringence model (SCBM), and forward scattering experiments on samples containing polystyrene microspheres, well-aligned glass fibers and polyacrylamide, we examine in detail the relationship between the MMPD parameters and the microscopic structure of the samples. The results show that the spherical scatterers and birefringent medium contribute to depolarization and retardance respectively, but the cylindrical scatterers contribute to both. Retardance due to the cylindrical scatterers changes with their density, size and order of alignment. Total retardance is a simple sum of both contributions when cylinders are in parallel to the extraordinary axis of birefringence.

Study on retardance due to well-ordered birefringent cylinders in anisotropic scattering media

Abstract. We report an anisotropic tissue model containing well-ordered birefringent cylinders. Using simulations and experiments, we examined the different polarization features for nonbirefringent and birefringent cylinders and analyzed the influence of the birefringent cylinders on the retardance obtained from Mueller matrix polar decomposition. For the well-ordered birefringent cylinders, retardance increases linearly with the intrinsic birefringence and the scattering coefficient. Furthermore, the cylinders with a larger diameter generate more retardance. Compared with the cylinder-birefringence model, in which birefringent medium exists between the scatterers, the intrinsic birefringence on the cylinders usually contributes much less to the total retardance.

Mueller polarimetry for the detection of cancers

Polarization measurements allow one to enhance imaging contrast of superficial tissues and obtain new polarization sensitive parameters for better description of the micro- and macro- structural and optical properties of complex tissues. Since the majority of cancers originate in the epithelial layer, probing the morphological and pathological changes in the superficial tissues using an expended parameter set and with improved spatial resolution and contrasts will lead to new clues on the early clinical detection of cancers. In this wok, we carry out polarization imaging on cancerous tissues and look for cancer specific features. Using a scattering model, which approximates the anisotropic biological tissues to a mixture of spherical and cylindrical scatterers imbedded in birefringent ambient media, and a Monte Carlo simulation program, we examine the relationship between the micro-structure of the model and the characteristic polarization features. The studies help to understand the contrast mechanism of polarization sensitive measurements for different cancers and provide the basis for potential clinical applications.