SignificanceMost biological fibrous tissues have anisotropic optical characteristics, which originate from scattering by their fibrous microstructures and birefringence of biological macromolecules. The orientation-related anisotropic interpretation is of great value in biological tissue characterization and pathological diagnosis.AimWe focus on intrinsic birefringence and form birefringence in biological tissue samples. By observing and comparing the forward Mueller matrix of typical samples, we can understand the interpretation ability of orientation-related polarization parameters and further distinguish the sources and trends of anisotropy in tissues.ApproachFor glass fiber, silk fiber, skeletal muscle, and tendon, we construct a forward measuring device to obtain the Mueller matrix image and calculate the anisotropic parameters related to orientation. The statistical analysis method based on polar coordinates can effectively analyze the difference in anisotropic parameters.ResultsFor those birefringent fibers, the statistical distribution of fast-axis values derived from Mueller matrix polar decomposition was found to exhibit bimodal characteristics, which is a key point in distinguishing the single-layer birefringent fiber sample from a layered, multioriented fibrous sample. The application conditions and interference factors of anisotropic orientation parameters are analyzed. Based on the parameters extracted from the orientation bimodal distribution, we can evaluate the relative change trend of intrinsic birefringence and form birefringence in anisotropic samples.ConclusionsThe cross-vertical bimodal distribution of the fast axis of anisotropic fibers is beneficial to accurately analyze the anisotropic changes in biological tissues. The results imply the potential of anisotropic orientation analysis for applications in pathological diagnosis.
In polarization imaging, circular and linear polarization are conventionally used for incident light detection. However, relying solely on these modes may lead to a loss of crucial polarization data. This study expands the incident polarization state from a single point on the Poincaré sphere to its entire surface, yielding the Global-Polarization Stokes Ellipsoids (GPSE). GPSE offers an intuitive representation of polarization response discrepancies. It reveals distinct characteristics when birefringence and scattering effects act independently and analyzes their coupled effects in concurrent operation. In systems with both birefringence and scattering, GPSE parameters provide a robust characterization of anisotropy, overcoming issues for linear phase retardation, like phase wrapping and helicity flip associated with circular polarization. This approach provides a novel perspective and methodology for polarization imaging and information extraction.
The identification of suspended particulate matter has always been an important issue of concern in the field of public health and environmental monitoring. Polarimetry has the advantage of non-invasive, label-free and sensitive to microstructure. The previous work realized the single-particle analysis of atmospheric aerosols based on polarization measurements. While progress has been made in the field of inversion of physical properties of single component aerosols, this paper further focuses on the multi-component mixing problem, and investigate how to apply polarization index system and corresponding data analysis to a wider range of application environments and provide clearer analysis of multi-component aerosol properties. Based on the multi-angle polarization scattering measurement instrument for suspended aerosols, the real-time experimental results of five typical environmental pollutants including motor vehicle exhaust, blind coal, coal, biomass combustion and dust are obtained. The central spectrum and distribution spectrum of 16 polarization indicators at 30°, 60°, 85° and 115° are established firstly. Then, the source identification of the complex component aerosols is solved by nonnegative linear least squares method, and the residual sum of squares is applied to quantitatively describe the accuracy of the source analysis. Compared with the classification method based on the central spectrum of multidimensional polarization index group, the method based on the distribution spectrum presents higher accuracy in source apportionment, which further confirmed the feasibility of realizing a refined aerosol characterization using single particle polarization scattering index and its statistical distribution.
The Mueller matrix encompasses polarization information, correlated with microstructure and optical properties. However, coupling effects complicate the retrieval of anisotropy source values. To address this, we propose a novel approach of mapping the Mueller matrix onto the Poincaré sphere and introduce a set of Global-Polarization Stokes Ellipsoids (GPSE) parameters to potentially retrieve two primary anisotropic sources: cylinder scattering and birefringence. Using porcine skeletal muscle as the reference object, we establish a database of Mueller matrices and GPSE via Monte Carlo simulation and train regression models based on multi-layer perceptron (MLP). Experimental results demonstrate that GPSE achieves comparable or even better prediction performance for anisotropy numerical values compared to the Mueller matrix model, indicating that GPSE parameters effectively contain anisotropy information present in the Mueller matrix. With an intuitive expression form and sensitivity to anisotropy, GPSE holds great potential in retrieving the values of anisotropic sources in tissues.
In this paper, we have built a Stokes imaging microscope system with a large field of view, and then validated the system. Because of the thin pathology sections and the low signal-to-noise ratio of Stokes imaging, accurate measurements of the weaker polarization signals are required. So at the light source side, we added a beam shaping module to make the distribution of light intensity more uniform. In addition, we used air as a standard sample to calibrate the measurement results, which makes the results more accurate. The specific slide scanning process is also presented in this paper, and we have used the solution to test it on actual pathology sections, and the experimental results show that the complete system works well and has the potential to assist in pathology analysis.
Polarization is a non-invasive optical technique and has become an emerging new tool in biomedicine studies due to its sensitivity to microstructure. The development of fast polarization techniques has enabled the application of polarimetry not only include static samples such as pathological sections, but also contain dynamic samples such as the process of tissue optical clearing (TOC). Dehydration is one of the important mechanisms of TOC which can result in the changes in tissue anisotropy, samples with different structures will show different characteristics in dehydration. In this study, three kinds of tissues with different degree of anisotropic including skeletal muscle, skin and fat are employed. We extracted and compared the temporal polarization parameters of several samples which may be related to the properties of microstructures. Monte Carlo (MC) simulation was combined to further explore the relationship between temporal polarization parameters and anisotropy of the sample. We first verified the main mechanisms of dehydration in spherecylinder birefringence model (SCBM). Then the optical properties of the microstructure in the model were changed to explore their influence on the polarization parameters. By analyzing the polarization parameters extracted from temporal Stokes images and Monte Carlo simulation, we can present polarization parameters to characterize microstructures of biological tissues.
Polarization measurement technology can detect the microscopic structure information from biological samples. However, for biological samples with weak scattering effect, the optical signal obtained by the detector will contain a large amount of zero-frequency light without scattering, which makes it difficult to effectively extract the polarization information of the samples with weak scattering effect. Therefore, in this study, we introduce spatial filtering technique into polarization measurement. In the experimental setup, a spatial filter is placed in the rear focal plane of the objective lens to block the zero-frequency light, so as to realize the selection of scattered photons. A red LED with the wavelength of 633nm was used as the lighting source. The measurement of polarization information is based on the dual-rotating quarter-wave plate method. Considering the widespread presence of spherical and columnar scatterers in biological systems, Hacat cells and biological fibers were selected for the experiment. By comparing with the polarization data without spatial filtering, we found that the polarization parameter obtained after the high pass filtering measurement can better characterize the samples.
Polarization imaging has shown the potential as a label-free tool in biomedical research due to its sensitivity to microstructures, especially the anisotropy analysis in pathological diagnosis. The digital pathology based on Mueller matrix systems has developed rapidly in recent years, and gradually progressed from qualitative to quantitative recognition. However, traditional critical illumination used in Mueller microscopes is likely to generate non-uniform projection accompanied by spatially varying irradiance, possibly due to unaligned optics, dust, nonuniform light sources, vignetting, etc. The non-uniform illumination results in artifacts in polarization images when stitching adjacent images to obtain a polarized image of the full sample, limiting the increase of the field of view (FOV). Therefore, a Mueller matrix microscope system with flat-field illumination and with motorized two-axis stage is proposed, we minimize the artifacts caused during splicing by uniform illumination, as well as increase the signal-to-noise (SNR) in the whole polarization images. The comparison of the real pathological sections under flat-field and wide-field illumination confirms the potential of large FOV imaging, which allows the structure of the sample to be presented more completely, laying the foundation for future pixel-level polarization digital pathology.
Significance: Reflection Mueller matrix imaging is suitable for characterizing the microstructure of bulk specimens and probing dynamic processes in living animals, there are always demands for speed and accuracy for such applications to avoid possible artifacts and reveal a sample’s intrinsic properties.Aim: To demonstrate a design of collinear reflection Mueller matrix fast imaging microscope based on dual division of focal plane (DoFP) polarimeters (DoFPs-CRMMM) which has high measurement speed and accuracy.Approach: In DoFPs-CRMMM, to improve the measurement speed, we applied the dual DoFP polarimeters design on the collinear reflection system for the first time to achieve fast imaging in about 2 s. To improve the measurement accuracy, we improved the double-pass eigenvalue calibration method (dp-ECM) by background light correction, and explored the optimization of the set of reference samples.Results: DoFPs-CRMMM was applied to measure the standard polarization samples and monitor the tissue optical clearing process of an artificial layered bulk tissue. Results show that the system has satisfactory performance which can capture the variation of polarization properties during the dynamic process.Conclusions: We present the establishment and demo application of DoFPs-CRMMM. The measurement speed can be further accelerated for potential applications in monitoring dynamic processes or living biomedical systems.
Polarimetry is sensitive to the microstructures and has its advantages in characterizing the tissue microstructures. Our previous work on dynamic polarization changes with tissue clearing has investigated the tissue variations by using glycerol,saturated sucrose and formamide.In this study, we use a fast Mueller matrix microscope to quantitatively compare the different mechanisms of two clearing agents: glycerol and formamide. We obtain the temporal Mueller matrix images with an interval of 15 seconds and extract the temporal features of polarization parameters. Except the depolarization and linear retardance, we also analyze Mueller matrix transformation (MMT) parameters and rotation invariants derived from Mueller matrices. The former is used to characterize the microscale anisotropy of scattering media, and the latter is suitable for assessing the breaking of symmetries of scattering matrix. These Mueller matrix parameters convey the micro characteristic of biological tissues, and then help to explore and explain the microstructural changes of tissue properties by optical clearing.
A common polarization measurement system consists of a quarter-wave plate and a linear polarizer, and the rotation of the wave plate can provide different phase retardance. However, the rotating phase retarder will introduce some unwanted frequency components in the light intensity signal, which may affect the correct information extraction for dynamic observation of the optical process. In this work, we analyzed the effective working frequency band of the polarization measurement system and pointed out how to judge the reliability of dynamic periodic polarization signals. We present the parameter selection strategy of the cutoff frequency of the filter, sampling frequency and rotation angular velocity for a specific dynamic polarization change of scattered light. Finally, we apply our work in the polarization monitoring of tissue optical clearing and show the improvement of the measurement stability and accuracy.
Tissue optical clearing techniques have become more and more prominent in biomedical applications, since they can reduce scattering and improve the imaging depth, resolution and contrast. Polarization is sensitive to the microstructure of tissues, when apply the rapid Stokes imaging method to monitor the process of optical tissue clearing, we observe that the polarization parameters oscillate periodically during clearing. A series of experiments have been designed to verify the truth of oscillations, we first eliminate the influence of system noise by measuring air and other polarization optics, the system error is less than 1% and is stable, then we analyze the impacts from optical clearing agents, we take quartz plate, the quartz plate with saturated sucrose solution, the fact is that there are slight fluctuations in polarization parameters but no oscillations. However, when we test the porcine skin which immersed in optical clearing agents, there are significant oscillations which show periodicity in polarization parameter, the oscillation cycle is about 40s and the oscillation amplitudes become smaller with the increase of immersion time. Finally, we imaging the samples which have completed optical clearing and no oscillation is found. By these series experiments, we confirm the truth of oscillations of the polarization parameters during clearing, and we believe these are connected with the mechanisms of the clearing which need further study.
Single suspended particle detection and recognition are tasks of significance in the context of both biomedical science and environment monitoring. In this work, we develop a system which is capable of both fluorescence and polarization real-time measurement for single suspended particle in the air. In our system, laser of 523nm is generated in light source and adjusted to light sheet in the detection area. Suspended particles fly through detection area and we real-time collect signals on both scattering, fluorescence and polarization channels for each particle. Our system provides the ability for further research on the airborne transmission route for pathogen and real-time detection of toxic pollutants in aerosol which usually emitting fluorescence for specific wavelength laser exciting.
Polarization imaging has shown great potentials in biomedical studies, due to its sensitivity to microstructural changes and anisotropic optical effects in biological tissues and contrast between lesion site and normal tissue. However, for total polarization measurement, no matter Muller matrix or Stokes vectors, their imaging processes are both time-consuming and not suitable for dynamic physiological monitoring. In this study, we proposed a method to obtain rapid continuous Stokes images and present it application in tissue characterization with clearing. We use single rotating retarder configuration to attain 2D Stokes vector images, the tissue clearing process and the Stokes measurement are carried synchronously on our vertical experimental device. According to the representation of the Stokes vectors on the Poincare sphere, we extract the linear-retardance and circular-depolarization parameters to characterize the microstructures of biological samples, and valid them by two tissue experiments. We show the dynamic Stokes imaging sequences of two types of in vitro tissue samples with clearing on the resolution board, and evaluate the clearing induced temporal variations quantitatively based on the polarization parameters. These experimental results demonstrate the feasibility of our rapid Stokes imaging based on Stokes measurement, implying a potential application in the tissue administration and physiological process.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.