Diagnostic photomedicine: probing biological tissues with polarized light

Upon illumination by ultraviolet light, many animal species emit light through fluorescence processes arising from fluorophores embedded within their biological tissues. Fluorescence studies in living organisms are however relatively scarce and so far limited to the linear regime. Multiphoton excitation fluorescence analyses as well as nonlinear optical techniques offer unique possibilities to investigate the effects of the local environment on the excited states of fluorophores. Herein, these techniques are applied for the first time to study of the naturally controlled fluorescence in insects. The case of the male Hoplia coerulea beetle is investigated because the scales covering the beetle’s elytra are known to possess an internal photonic structure with embedded fluorophores, which controls both the beetle’s coloration and the fluorescence emission. An intense two-photon excitation fluorescence signal is observed, the intensity of which changes upon contact with water. A third-harmonic generation signal is also detected, the intensity of which depends on the light polarization state. The analysis of these nonlinear optical and fluorescent responses unveils the multi-excited states character of the fluorophore molecules embedded in the beetle’s elytra. The role of form anisotropy in the photonic structure, which causes additional tailoring of the beetle’s optical responses, is demonstrated by circularly polarized light and nonlinear optical measurements.

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Mueller matrix decomposition for polarized light assessment of biological tissues

Journal of Biophotonics ◽

10.1002/jbio.200810040 ◽

2009 ◽

Vol 2 (3) ◽

pp. 145-156 ◽

Cited By ~ 90

Author(s):

Nirmalya Ghosh ◽

Michael F. G. Wood ◽

Shu-hong Li ◽

Richard D. Weisel ◽

Brian C. Wilson ◽

...

Keyword(s):

Polarized Light ◽

Matrix Decomposition ◽

Biological Tissues ◽

Mueller Matrix

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Polarized Light Assessment of Complex Turbid Media Such as Biological Tissues Us- ing Mueller Matrix Decomposition

Handbook of Photonics for Biomedical Science ◽

10.1201/9781439806296-15 ◽

2010 ◽

pp. 289-318

Keyword(s):

Polarized Light ◽

Matrix Decomposition ◽

Biological Tissues ◽

Mueller Matrix ◽

Turbid Media

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Hyperelastic modelling of arterial layers with distributed collagen fibre orientations

Journal of The Royal Society Interface ◽

10.1098/rsif.2005.0073 ◽

2005 ◽

Vol 3 (6) ◽

pp. 15-35 ◽

Cited By ~ 1189

Author(s):

T. Christian Gasser ◽

Ray W Ogden ◽

Gerhard A Holzapfel

Keyword(s):

Structural Model ◽

Mechanical Response ◽

Constitutive Relations ◽

Polarized Light ◽

Collagen Fibre ◽

Middle Layer ◽

Biological Tissues ◽

Free Energy Function ◽

Collagen Fibres ◽

Small Pitch

Constitutive relations are fundamental to the solution of problems in continuum mechanics, and are required in the study of, for example, mechanically dominated clinical interventions involving soft biological tissues. Structural continuum constitutive models of arterial layers integrate information about the tissue morphology and therefore allow investigation of the interrelation between structure and function in response to mechanical loading. Collagen fibres are key ingredients in the structure of arteries. In the media (the middle layer of the artery wall) they are arranged in two helically distributed families with a small pitch and very little dispersion in their orientation (i.e. they are aligned quite close to the circumferential direction). By contrast, in the adventitial and intimal layers, the orientation of the collagen fibres is dispersed, as shown by polarized light microscopy of stained arterial tissue. As a result, continuum models that do not account for the dispersion are not able to capture accurately the stress–strain response of these layers. The purpose of this paper, therefore, is to develop a structural continuum framework that is able to represent the dispersion of the collagen fibre orientation. This then allows the development of a new hyperelastic free-energy function that is particularly suited for representing the anisotropic elastic properties of adventitial and intimal layers of arterial walls, and is a generalization of the fibre-reinforced structural model introduced by Holzapfel & Gasser (Holzapfel & Gasser 2001 Comput. Meth. Appl. Mech. Eng . 190 , 4379–4403) and Holzapfel et al . (Holzapfel et al . 2000 J. Elast . 61 , 1–48). The model incorporates an additional scalar structure parameter that characterizes the dispersed collagen orientation. An efficient finite element implementation of the model is then presented and numerical examples show that the dispersion of the orientation of collagen fibres in the adventitia of human iliac arteries has a significant effect on their mechanical response.

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Graphics processing unit-accelerated Monte Carlo simulation of polarized light in complex three-dimensional media

10.1101/2022.01.13.476270 ◽

2022 ◽

Author(s):

Shijie Yan ◽

Steven L Jacques ◽

Jessica C. Ramella-Roman ◽

Qianqian Fang

Keyword(s):

Monte Carlo ◽

Graphics Processing Unit ◽

Three Dimensional ◽

Polarized Light ◽

Biological Tissues ◽

Dramatic Improvement ◽

Processing Unit ◽

Photon Propagation ◽

Spatially Resolved ◽

Massively Parallel Computing

Significance: Monte Carlo (MC) methods have been applied for studying interactions between polarized light and biological tissues, but most existing MC codes supporting polarization modeling can only simulate homogeneous or multi-layered domains, resulting in approximations when handling realistic tissue structures. Aim: Over the past decade, the speed of MC simulations has seen dramatic improvement with massively-parallel computing techniques. Developing hardware-accelerated MC simulation algorithms that can accurately model polarized light inside 3-D heterogeneous tissues can greatly expand the utility of polarization in biophotonics applications. Approach: Here we report a highly efficient polarized MC algorithm capable of modeling arbitrarily complex media defined over a voxelated domain. Each voxel of the domain can be associated with spherical scatters of various radii and densities. The Stokes vector of each simulated photon packet is updated through photon propagation, creating spatially resolved polarization measurements over the detectors or domain surface. Results: We have implemented this algorithm in our widely disseminated MC simulator, Monte Carlo eXtreme (MCX). It is validated by comparing with a reference CPU-based simulator in both homogeneous and layered domains, showing excellent agreement and a 931-fold speedup. Conclusion: The polarization-enabled MCX (pMCX) offers biophotonics community an efficient tool to explore polarized light in bio-tissues, and is freely available at http://mcx.space/.

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