For in-vivo polarimetry such as Mueller matrix endoscopy of human internal organ cavities, the complicated undulating tissue surfaces deliver an inescapable occurrence of oblique incidence, which induce a prominent aberration to backscattering tissue polarimetry. In this Letter, we quantitatively analyze such polarimetric aberration on polarization basic parameters derived from the Mueller matrix. A correlation heatmap is obtained as applicable criteria to select an appropriate incident angle for different polarization basic parameters. Based on the analyzing results, we propose two aberration optimization strategies of parameter selection and azimuth rotation, which are suitable for tissue samples with randomly and well-aligned fiber textures, respectively. Both strategies are demonstrated to be effective in the ex-vivo human gastric muscularis tissue experiment. The findings presented in this Letter can be useful to provide accurate polarization imaging results, widely applied on in-vivo polarimetric endoscopy for tissues with complicated surface topography.

Polarimetry is attracting increasing attention nowadays, due to its unique ability to obtain microstructural and optical information of tissue samples label-free.^{1 – 4} Among the available polarimetric techniques, Mueller matrix (MM) imaging can comprehensively characterize the polarization-related properties of media, including diattenuation, retardance, and depolarization, which are of great importance in biomedical studies and clinical trials.^{5 – 7} Recently, transmission MM microscopy has shown potential in detection of various abnormal and pathological tissues, such as breast cancer,⁸ cervical cancer,⁹ colon cancer,¹⁰ skin cancer,^11,12 liver cirrhosis,^13,14 gastrointestinal cancer,^15,16 thyroid cancer,¹⁷ and lung cancer.¹⁸ Meanwhile, the backscattering MM polarimetry provides a promising non-contact and quantitative tool for ex-vivo measurement of bulk tissue samples,^{6,7,19 – 22} in-vivo imaging of skin tissue,^{23 – 26} and endoscopic detection of internal organs.^{27 – 31}

Polarization imaging and sensing techniques have shown great potential for biomedical and clinical applications. As a novel optical biosensing technology, Mueller matrix polarimetry can provide abundant microstructural information of tissue samples. However, polarimetric aberrations, which lead to inaccurate characterization of polarization properties, can be induced by uneven biomedical sample surfaces while measuring Mueller matrices with complex spatial illuminations. In this study, we analyze the detailed features of complex spatial illumination-induced aberrations by measuring the backscattering Mueller matrices of experimental phantom and tissue samples. We obtain the aberrations under different spatial illumination schemes in Mueller matrix imaging. Furthermore, we give the corresponding suggestions for selecting appropriate illumination schemes to extract specific polarization properties, and then provide strategies to alleviate polarimetric aberrations by adjusting the incident and detection angles in Mueller matrix imaging. The optimized scheme gives critical criteria for the spatial illumination scheme selection of non-collinear backscattering Mueller matrix measurements, which can be helpful for the further development of quantitative tissue polarimetric imaging and biosensing.

As a complex anisotropic medium, variation in birefringence within biological tissues is closely associated with numerous physiological behaviors and phenomena. In this Letter, we propose a polarization feature fusion method and corresponding polarimetric parameters, which exhibit excellent performance of capturing the birefringence dynamic variation process in complex anisotropic media. By employing the feature fusion method, we combine and transform polarization basis parameters (PBPs) to derive fused polarization feature parameters (FPPs) with explicit expressions. Subsequently, we conduct Monte Carlo (MC) simulation to demonstrate the effectiveness of the proposed FPPs from two variation dimensions of birefringence direction 0 and modulus triangle n. Leveraging mathematical modeling and linear transformations, we investigate and abstract their response patterns concerning 0 and triangle n. Finally, the experiments confirm that the FPPs show superior adaptability and interpretability in characterizing the birefringence dynamic process of turbid media. The findings presented in this study provide new, to the best of our knowledge, methodological insights of information extraction for computational polarimetry in biomedical research. (c) 2024 Optica Publishing Group

Liver fibrosis is a response to chronic liver damage, causing the accumulation of extracellular components like collagen fibers. Accurate evaluation of fibrosis is key for predicting disease prognosis. Multiphoton microscopy (MPM) is an advanced technique that allows label-free imaging of biomedical tissues using femtosecond laser-induced nonlinear optical effects. In this study, hepatic tissue samples were imaged via MPM and then imaging data were analyzed with Hover-Net, a convolutional neural network. We find that MPM has the ability to directly observe fibrotic changes, and also find that the number of portal bile ducts are positively related to liver fibrosis and can be automatically identified by the Hover-Net. These findings suggest MPM combining with deep learning can assess liver fibrosis quickly and reliably without the need for exogenous contrast agents.