Polarimetry has a long and successful history in various forms of clear media. Driven by their biomedical potential, the use of the polarimetric approaches for biological tissue assessment has also recently received considerable attention. Specifically, polarization can be used as an effective tool to discriminate against multiply scattered light (acting as a gating mechanism) in order to enhance contrast and to improve tissue imaging resolution. Moreover, the intrinsic tissue polarimetry characteristics contain a wealth of morphological and functional information of potential biomedical importance. However, in a complex random medium-like tissue, numerous complexities due to multiple scattering and simultaneous occurrences of many scattering and polarization events present formidable challenges both in terms of accurate measurements and in terms of analysis of the tissue polarimetry signal. In order to realize the potential of the polarimetric approaches for tissue imaging and characterization/diagnosis, a number of researchers are thus pursuing innovative solutions to these challenges. In this review paper, we summarize these and other issues pertinent to the polarized light methodologies in tissues. Specifically, we discuss polarized light basics, Stokes-Muller formalism, methods of polarization measurements, polarized light modeling in turbid media, applications to tissue imaging, inverse analysis for polarimetric results quantification, applications to quantitative tissue assessment, etc.

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Tissue polarimetry: concepts, challenges, applications, and outlook

We report a new type of holographic interface, which is able to manipulate the three fundamental properties of light (phase, amplitude, and polarization) over a broad wavelength range. The design strategy relies on replacing the large openings of conventional holograms by arrays of subwavelength apertures, oriented to locally select a particular state of polarization. The resulting optical element can therefore be viewed as the superposition of two independent structures with very different length scales, that is, a hologram with each of its apertures filled with nanoscale openings to only transmit a desired state of polarization. As an implementation, we fabricated a nanostructured holographic plate that can generate radially polarized optical beams from circularly polarized incident light, and we demonstrated that it can operate over a broad range of wavelengths. The ability of a single holographic interface to simultaneously shape the amplitude, phase, and polarization of light can find widespread applications in photonics.

Nanostructured holograms for broadband manipulation of vector beams.

This paper aims to review recent results on the optical clearing of the naturally turbid biological tissues and blood using the optical immersion technique, which is well known in physical science and is applied for the reduction of light scattering and undesirable reflections in the optical system. Basic principles of the technique, its advantages, limitations and future are discussed. The refractive index matching concept for enhancement of in-depth light penetration into tissues and blood is presented on the basis of in vitro and in vivo studies using optical spectroscopy, polarization and coherence-domain techniques. The index matching of scatterers and ground matter by means of administration of clearing agents is under discussion. The optical properties of tissues with basic multiple scattering, which are transformed to a low scattering mode, are analysed. It is shown that light reflection, transmission, scattering and polarization can be effectively controlled. The possibilities of using the optical immersion method for diagnostic purposes based on contrasting of abnormalities, on in-depth profiling of tissue and blood and on monitoring of endogenous and exogenous matter diffusion within tissue are demonstrated.

https://iopscience.iop.org/article/10.1088/0022-3727/38/15/001/pdf

Optical clearing of tissues and blood using the immersion method

Quantum approaches relying on entangled photons have been recently proposed to increase the efficiency of optical measurements. We demonstrate here that, surprisingly, the use of classical light with entangled degrees of freedom can also bring outstanding advantages over conventional measurements in polarization metrology. Specifically, we show that radially polarized beams of light allow to perform real-time single-shot Mueller matrix polarimetry. Our results also indicate that quantum optical procedures requiring entanglement without nonlocality can be actually achieved in the classical optics regime.

https://iopscience.iop.org/article/10.1088/1367-2630/16/7/073019/pdf

Classical entanglement in polarization metrology

In this article, we discuss the optical immersion method based on refractive index matching of scatterers (e.g., collagen, elastin fibers, cells and cell compartments) and the ground material (interstitial fluid and/or cytoplasm) of tissue and blood under the action of exogenous optical clearing agents. We analyze the optical clearing of fibrous and cell-structured tissues and blood from the point of view of receiving more valuable, normally hidden, information from spectroscopic and polarization measurements, confocal microscopy, optical coherence and optical projection tomography, as well as from nonlinear spectroscopies, such as two-photon fluorescence and second-harmonic generation techniques. Some important applications of the immersion technique to glucose sensing, drug delivery monitoring, improvements of image contrast and imaging depth, nondistortive delivery of laser radiation and precision tissue laser photodisruption, among others, are also described.

Tissue optical immersion clearing

Tissue Structure and Optical Models.- Polarized Light Interactions with Weakly Scattering Media.- Polarized Light Interactions with Strongly Scattering Media.- Polarization Properties of Tissues and Phantoms.- Polarization-Dependent Interference of Multiply Scattered Light.- Decay of Light Polarization in Random Multiple Scattering Media.- Degree of Polarization in Laser Speckles from Turbid Media.- Monte Carlo Modeling of Polarization Propagation.- Polarization-Sensitive Optical Coherence Tomography.- Biomedical Diagnostics and Imaging.

Optical polarization in biomedical applications

Statistical properties of GB speckle patterns: Influence of the phase modulation depth of the synthesized GB apertures

Small-angle polarimetry as a technique for identification of nucleotide sequences in bioinformatics

The modern coherent-optical methods based on the processing of the detected multiple-scattered by randomly inhomogeneous media signals. The statistical analysis of the stochastic intensity distributions caused by the multiple scattered radiation (evaluating such characteristic as flicker index, contrast, structural and correlation functions, etc.) give the opportunity to evaluate the structural morphology of the investigate media (concentration and shape of inhomogeneities, features of the organization of the structure) and the dynamic processes occurring inside the media. In this work the investigation of the water solutions of technical or food gelatin with added TiO2 nanoparticles and foamy phantoms by use of the full field speckle correlometry method is represented.

Dmitrij A Zimnyakov

Papers

Optical polarization in biomedical applications

Statistical properties of GB speckle patterns: Influence of the phase modulation depth of the synthesized GB apertures

Small-angle polarimetry as a technique for identification of nucleotide sequences in bioinformatics

Speckle correlometry processing algorithms in application to randomly inhomogeneous media study

On the Minimum Length of Fluorescence Enhancement upon Laser Pumping of Randomly Inhomogeneous Media