偏振光成像技术用于肿瘤病变检测的研究进展

偏振光成像是一种非标记、无损伤检测技术,它与现有非偏振光学方法硬件兼容,但能提供更丰富的样品结构和光学信息,并且对亚波长微观结构变化十分敏感.最近,偏振光成像方法在生物医学,特别是肿瘤癌症检测领域显示出很好的应用前景.本文介绍了常用的偏振光散射成像方法,包括偏振差、偏振度、旋转线偏振成像、偏振显微、穆勒矩阵成像等,并展示这些偏振方法在生物医学领域,特别是癌症检测方面的最新研究进展.目前偏振差、偏振度等成像方法已被初步用于皮肤癌的诊断,而穆勒矩阵包含更为丰富的组织微观结构信息,因而具有更好的诊断应用前景.通过对穆勒矩阵进行分解、变换等处理,可获得具有明确物理意义的成像参数,并发展为针对不同应用的特异性方法.目前,随着新型光源、偏振器件和探测器的出现,特别是数据计算处理能力的急剧提升,偏振成像在数据解释和测量方法方面的研究快速发展,已经在生物医学领域显示出很好的应用前景.     

Detection and identification of optical activity using polarimetry – applications to biophotonics,biomedicine and biochemistry

Polarized light that is reflected or transmitted through chiral specimens can be used to detect and identify biological and chemical materials including human tissue. The determination of the silent footprints of the chiral properties of the biological materials on scattered polarized light is the basis for these investigations. It is of primary importance to identify which combinations of the elements of the Mueller matrix for reflected or for transmitted light can be used to determine the optical activity of the biochemical materials. The optical activity of chiral materials is characterized by optical rotation and circular dichroism. The explicit analytical dependence of these specific elements of the Mueller matrix, upon the angles of incidence and scatter, upon the wavelength and upon the type of chirality has the potential to provide experimentalists with guidance in determining the optimum use of optical polarimetric scatterometers. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Alignment maps of tissues: I. Microscopic elliptical polarimetry

An automated method for generating a fiber alignment map in tissues, tissue-equivalents, and other fibrillar materials exhibiting linear and circular optical properties and scattering is presented. This method consists of interrogating the sample with elliptically polarized light from a rotated quarter-wave plate and an effective circular analyzer, and implementing nonlinear regression techniques to estimate parameters defining the optical properties of the optic train and the sample. Thus, an account is made for imperfect and misaligned optic elements. The optic train was modeled using the Mueller matrix representation and the combined sample properties by an exponential matrix. Because a sample's Mueller matrix does not uniquely determine the linear, circular, or scattering properties, the circular properties and effective scattering are estimated for a matched isotropic sample to determine and correct for the linear birefringence of an aligned sample. The method's utility is demonstrated by generating an alignment map of an arterial media-equivalent, a relevant test case because of its circumferential alignment and thus showing the method's sample orientation independence.     

Changes in DNA superhelical density monitored by polarized light scattering.

Linear and circular lambda-DNA at different ethidium bromide concentrations have been studied by means of polarized light scattering, namely the S14, S34, S33 and S13 elements of Mueller matrix. While S33 at low angle appears well correlated with the total light scattering evaluated by optical density measurements at 632.8 nm for linear and circular DNA of the same mass, the magnitude and slope of the S14, S34 and S13 signals display significant changes for the circular lambda-DNA depending on the degree of negative superhelical density as induced by the different ethidium bromide concentrations. At the same time, for linear lambda-DNA the signal remains invariant, making explicit for the differential scattering of polarized light the possibility to obtain additional information by its angular dependence. Strikingly also the effect of 0.2% glutaraldehyde versus ethanol fixation on the native lambda-DNA structural properties appears to confirm earlier findings by other well-established probes. Results are discussed in terms of first physical principles and of their potential bearings towards our understanding of the mechanism controlling gene expression.     

Development of vacuum-ultraviolet circular dichroism measurement system using a polarizing undulator

We have developed an improved circular dichroism (CD) and linear dichroism (LD) simultaneous measurement system for the vacuum ultraviolet (VUV) region by polarization modulation techniques using a four-period Onuki-type crossed undulator as a polarized light source. The system has been constructed at the VUV beamline BL-5 in the electron storage ring TERAS, at AIST. Our improvements, in particular the adoption of an optical chopper as the detection method of incident light, have resulted in a flat baseline and a consequent simplification of the Mueller matrix calculation for our optical system. Based on the Mueller matrix calculation, we have successfully measured real VUV-CD and LD spectra of leucine films for wavelengths down to 160 nm with absolute optical constants. The obtained spectra show good consistency with spectra measured by conventional methods.     

Differential polarization imaging. II. Symmetry properties and calculations

Various differential polarization images or Mueller images of model objects are generated using the equations derived in the previous paper (paper I of this series). These calculated images include models of the higher-order organization of metaphase chromosomes, and show the applicability of the differential polarization imaging method to the elucidation of complex molecular organizations. Then, the symmetry behavior of the Mueller matrix elements upon infinitesimal rotations of the optical components about the optical axis of the imaging system is presented. It is shown that the rotational properties of the Mueller images can be used to eliminate the linear polarization contributions to the M14 and M44 images, which appear when these images are generated with imperfect circular polarizations. The relationships between the 16 bright-field Mueller images for four different media, i.e., linearly and circularly isotropic, circularly anisotropic, linearly anisotropic, and linearly and circularly anisotropic, are also derived. For the first three cases simple relationships between the Mueller images are found and phenomenological equations in terms of the optical coefficients are derived. In the last case there are no specific relationships between the Mueller images and instead we briefly present Schellman and Jensen's method for treating this type of medium. The criterion of spatial resolution between adjacent domains of different optical anisotropy is then derived. It is found that in transitions between domains of opposite anisotropy the classical Rayleigh limit must be replaced by a magnitude criterion which depends on the limits of the sensitivity of the detection. Finally, the feasibility of optical sectioning in differential polarization imaging is demonstrated.     

Assessment of tissue polarimetric properties using Stokes polarimetric imaging with circularly polarized illumination

Tissue‐depolarization and linear‐retardance are the main polarization characteristics of interest for bulk tissue characterization, and are normally interpreted from Mueller polarimetry. Stokes polarimetry can be conducted using simpler instrumentation and in a shorter time. Here, we use Stokes polarimetric imaging with circularly polarized illumination to assess the circular‐depolarization and linear‐retardance properties of tissue. Results obtained were compared with Mueller polarimetry in transmission and reflection geometry, respectively. It is found that circular‐depolarization obtained from these 2 methods is very similar in both geometries, and that linear‐retardance is highly quantitatively similar for transmission geometry and qualitatively similar for reflection geometry. The majority of tissue circular‐depolarization and linear‐retardance image information (represented by local image contrast features) obtained from Mueller polarimetry is well preserved from Stokes polarimetry in both geometries. These findings can be referred to for further understanding tissue Stokes polarimetric data, and for further application of Stokes polarimetry under the circumstances where short acquisition time or low optical system complexity is a priority, such as polarimetric endoscopy and microscopy.      

Polarized diffuse reflectance measurements on cancerous and noncancerous tissues

We report the measurement of polarization parameters (linear retardance, diattenuation and depolarization) of normal and malignant tissue from human oral cavity and breast over the spectral range 390 nm to 550 nm. These parameters were determined using the 3 × 3 Mueller matrix, the elements of which could be determined using linear polarization measurements only. The significant differences observed in the polarization parameters of the normal and malignant tissues appear to arise because of the changes in the collagen matrix in the two tissue types. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phasor approach of Mueller matrix optical scanning microscopy for biological tissue imaging

Mueller matrix microscopy is an advanced imaging technique providing a full characterization of the optical polarization fingerprint of a sample. The Lu-Chipman (LC) decomposition, a method based on the modeling of elementary polarimetric arrangements and matrix inversions, is the gold standard to extract each polarimetric component separately. However, this models the optical system as a small number of discrete optical elements and requires a priori knowledge of the order in which these elements occur. In stratified media or when the ordering is not known, the interpretation of the LC decomposition becomes difficult. In this work, we propose a new, to our knowledge, representation dedicated to the study of biological tissues that combines Mueller matrix microscopy with a phasor approach. We demonstrate that this method provides an easier and direct interpretation of the retardance images in any birefringent material without the use of mathematical assumptions regarding the structure of the sample and yields comparable contrast to the LC decomposition. By validating this approach through numerical simulations, we demonstrate that it is able to give access to localized structural information, resulting in a simple determination of the birefringent parameters at the microscopic level. We apply our novel, to our knowledge, method to typical biological tissues that are of interest in the field of biomedical diagnosis.     

Effects of light regimes on anther culture response in bread wheat

This experiment was initiated to further test the effects of light regimes during callus induction and plant regeneration on anther culture response of spring wheat (Triticum aestivum L.). Spring wheat cultivars 'Edwall' and 'WA 7176' with high callus induction from anther culture but low green plant production were used. Different gro-lux light and dark regimes during callus induction, and gro-lux light and fluorescent light regimes during plant regeneration were used. Callus induction decreased significantly at relatively high light intensity (315 μmol m⁻² s⁻¹) applied at any period of culture when compared to continuous dark. Light regimes used continuously and from the 15^th to the last day of callus induction also had a significant negative effect on plant regeneration compared to continuous dark and light application in the first half of callus induction. During plant regeneration, '15 day dark + 7 day gro-lux light' significantly increased plant regeneration compared to both 'gro-lux' and 'fluorescent light' regimes. Light regimes during both callus induction and plant regeneration and their interaction effects were found to be highly significant on green plant proportion and green plant yield. 'Continuous light' application during callus induction increased green plant proportion more than other applications in contrast to its negative effect on plant regeneration. During plant regeneration, '15 day dark + 7 day gro-lux light' had the higher green plant proportion compared to only 'fluorescent light' and only 'gro-lux light'. The highest green plant yields were obtained from '15 day dark + 7 day gro-lux light' during plant regeneration in combination with either 'continuous dark' or 'continuous light' regimes during callus induction. This revised version was published online in June 2006 with corrections to the Cover Date.     

Perceiving polarization with the naked eye: characterization of human polarization sensitivity

Like many animals, humans are sensitive to the polarization of light. We can detect the angle of polarization using an entoptic phenomenon called Haidinger''s brushes, which is mediated by dichroic carotenoids in the macula lutea. While previous studies have characterized the spectral sensitivity of Haidinger''s brushes, other aspects remain unexplored. We developed a novel methodology for presenting gratings in polarization-only contrast at varying degrees of polarization in order to measure the lower limits of human polarized light detection. Participants were, on average, able to perform the task down to a threshold of 56%, with some able to go as low as 23%. This makes humans the most sensitive vertebrate tested to date. Additionally, we quantified a nonlinear relationship between presented and perceived polarization angle when an observer is presented with a rotatable polarized light field. This result confirms a previous theoretical prediction of how uniaxial corneal birefringence impacts the perception of Haidinger''s brushes. The rotational dynamics of Haidinger''s brushes were then used to calculate corneal retardance. We suggest that psychophysical experiments, based upon the perception of polarized light, are amenable to the production of affordable technologies for self-assessment and longitudinal monitoring of visual dysfunctions such as age-related macular degeneration.     

Simulation and Analytical Study of Optical Complex Field in Nano-corral Slits Plasmonic Lens

Although spiral plasmonic lens has been proposed as circular polarization analyzer, there is no such plasmonic nanostructure available for linear polarization. In the current work, we have designed nano-corral slits (NCS) plasmonic lens, which focuses the x- and y-polarized light into spatially distinguished plasmonic fields. We have calculated analytically and numerically the electric field intensity and phase of the emission from nano-corral slits plasmonic lens with different pitch lengths under various polarizations of the illumination. It has been shown that one can control the wave front of the output beam of these plasmonic lenses by manipulating the illumination of both circular and linear polarization. Our theoretical study in correlation with FDTD simulation has shown that NCS plasmonic lens with pitch length equal to λ_spp produces scalar vortex beam having optical complex fields with helical wave front and optical singularity at the center under circular polarization of light. When NCS lens (pitch = λ_spp) is illuminated with linearly polarized light, it exhibits binary distribution of phase with same electric field intensity around the center. However, with pitch length of 0.5λ_spp, NCS shows linear dichroism under linearly polarized illumination unlike spiral plasmonic lens (SPL) eliminating the use of circularly polarized light. Optical complex fields produced by these NCS plasmonic lenses may find applications for faster quantum computing, data storage, and telecommunications.

     

Complex Polarization Response in Plasmonic Nanospirals

Archimedean nanospirals exhibit many far-field resonances that result from the lack of symmetry and strong intra-spiral plasmonic interactions. Here, we present a computational study, with corroborating experimental results, on the plasmonic response of the 4π Archimedean spiral as a function of incident polarization, for spirals in which the largest linear dimension is less than 550 nm. We discuss the modulation of the near-field structure for linearly and circularly polarized light in typical nanospiral configurations. Computational studies of the near-field distributions excited by circularly polarized light illustrate the effects of chirality on plasmonic mechanisms, while rotation of linearly polarized light provides a detailed view of the effects of broken symmetry on nanospiral fields in any given direction in the plane of the spiral. The rotational geometry exhibits a preference for circular polarization that increases near-field enhancement compared to excitation with linearly polarized light and exchanges near-field configurations and resonant modes. By analyzing the effects of polarization and wavelength on the near-field configurations, we also show how the nanospiral could be deployed in applications such as tunable near-field enhancement of nonlinear optical signals from chiral molecules.     

Investigation on the potential of Mueller matrix imaging for digital staining

Digital staining based on Mueller matrix measurements and their derivatives was investigated. Mueller matrix imaging was performed at the microscopic level on gastric tissue sections. Full Mueller matrices (4 × 4) were reconstructed using recorded images, followed by the extraction of polarization parameters. The most effective parameters and their combinations were extracted from Mueller matrix elements, principal component scores and polarization parameters respectively to classify samples into three categories – i.e. cancer, dysplasia and intestinal metaplasia/normal glands for various regions of interest sizes. It was observed that two‐step classification yielded higher classification accuracy than the traditional one‐step classification and that pixel classification based on Mueller matrix elements yielded higher accuracy than that based on polarization parameters and derived principal components. Moreover, Mueller matrix images with a lower spatial resolution generated higher classification accuracy but those with a higher spatial resolution revealed more morphological details.ns.

The original stained image (top) and the digital staining image (bottom).     

Revisiting polarimetry near the isotropic point of an optically active,non‐enantiomorphous,molecular crystal

Accurate polarimetric measurements of the optical activity of crystals along low symmetry directions are facilitated by isotropic points, frequencies where dispersion curves of eigenrays cross and the linear birefringence disappears. We report here the optical properties and structure of achiral, uniaxial (point group D_2d) potassium trihydrogen di‐(cis‐4‐cyclohexene‐1,2‐dicarboxylate) dihydrate, whose isotropic point was previously detected (S. A. Kim, C. Grieswatch, H. Küppers, Zeit. Krist. 1993; 208:219–222) and exploited for a singular measurement of optical activity normal to the optic axis. The crystal structure associated with the aforementioned study was never published. We report it here, confirming the space group assignment I c2, along with the frequency dependence of the fundamental optical properties and the constitutive tensors by fitting optical dispersion relations to measured Mueller matrix spectra. k‐Space maps of circular birefringence and of the Mueller matrix near the isotropic wavelength are measured and simulated. The signs of optical rotation are correlated with the absolute crystallographic directions.     

Circular polarization vision in a stomatopod crustacean

We describe the addition of a fourth visual modality in the animal kingdom, the perception of circular polarized light. Animals are sensitive to various characteristics of light, such as intensity, color, and linear polarization [1, 2]. This latter capability can be used for object identification, contrast enhancement, navigation, and communication through polarizing reflections [2-4]. Circularly polarized reflections from a few animal species have also been known for some time [5, 6]. Although optically interesting [7, 8], their signal function or use (if any) was obscure because no visual system was known to detect circularly polarized light. Here, in stomatopod crustaceans, we describe for the first time a visual system capable of detecting and analyzing circularly polarized light. Four lines of evidence-behavior, electrophysiology, optical anatomy, and details of signal design-are presented to describe this new visual function. We suggest that this remarkable ability mediates sexual signaling and mate choice, although other potential functions of circular polarization vision, such as enhanced contrast in turbid environments, are also possible [7, 8]. The ability to differentiate the handedness of circularly polarized light, a visual feat never expected in the animal kingdom, is demonstrated behaviorally here for the first time.     

基于旋转偏振角的线偏振扫描成像方法研究

提出一种基于旋转偏振角的新的偏振光成像方法:改变入射线偏振光偏振角和检偏角,采集样品图像系列,总结出背向散射光2个正交偏振分量的光强差关于入射线偏振光偏振角和检偏角的函数关系式.通过对模拟散射介质,猪肉脂肪,猪肉骨骼肌和牛肉骨骼肌等样品进行实验,论证了偏振差函数式中各个参数与样品光学特性之间的联系,并从中提取出2个相互独立的参数,分别表征样品的纤维方向角和光学各向异性度,从而实现对样品浅表层光学特性进行定量测量.和普通光强图像相比,用这些独立的光学信息生成不同基色的图像,能更直观明了地区分组织结构差异,具有潜在的临床医学应用价值,如成为一种皮肤疾病、皮肤损伤的检测方法.     

Circular Polarization of Transmitted Light by Sapphirinidae Copepods

Circularly polarized light, rare in the animal kingdom, has thus far been documented in only a handful of animals. Using a rotating circular polarization (CP) analyzer we detected CP in linearly polarized light transmitted through epipelagic free living Sapphirina metallina copepods. Both left and right handedness of CP was detected, generated from specific organs of the animal''s body, especially on the dorsal cephalosome and prosome. Such CP transmittance may be generated by phase retardance either in the muscle fibers or in the multilayer membrane structure found underneath the cuticle. Although the role, if any, played by circularly polarized light in Sapphirinidae has yet to be clarified, in other animals it was suggested to take part in mate choice, species recognition, and other forms of communication.

Highlights

Planktonic Sapphirinidae copepods were found to circularly polarize the light passing through them. Circular polarization may be created by unique, multilayered features of the membrane structure found under their cuticle or by organized muscle fibers.