This conference presentation was prepared for SPIE BiOS, 2024.

Polarized light interaction with media can reveal the microstructure and anisotropy of complex media beyond what can be obtained from scalar light interaction. Here, we present reciprocal polar decomposition for the backscattering Mueller matrices, a new Mueller matrix decomposition method for analyzing chiral and nonchiral complex media measured in reflection geometry. Reciprocal polar decomposition uniquely accounts for the reciprocity of the optical wave in forward and backward scattering paths. We demonstrate the superiority of the reciprocal polar decomposition against Lu-Chipman and differential Mueller matrix decompositions in various applications of backscattering polarimetry for birefringent targets, tissue sections, and chiral media. We also report examples where Lu-Chipman and differential decompositions produce incorrect media properties, whereas reciprocal polar decomposition succeeds. Reciprocal polar decomposition will open up diverse applications of backscattering polarimetry for biomedicine.

We present an advanced technique of polarized light microscopy (PLM) for the assessment of carious lesions, wherein the degree of polarization (DOP) is evaluated. Through modifications of a conventional PLM setup, images were generated by calculating the DOP from an image series of different linear polarization images acquired with a polarization camera. Demineralization is reliably displayed by the DOP in accordance with the common imaging methods. Evaluating the DOP by PLM allows the characterization of the different pathohistological zones of caries with a new quantitative approach.

Tooth color is an important parameter in cosmetic dentistry, to measure staining, effects of whitening products, or for matching the appearance of implants to neighboring teeth. The apparent color of teeth is affected by surface (extrinsic) and sub-surface (intrinsic) factors and is still assessed qualitatively by the dentist’s visual impression. This study used a new color polarization camera to quantify tooth color. Recent commercial availability of snapshot color polarization cameras offers a new approach to rapidly quantify tissue color with depth selectivity. We applied this technology to quantify tooth color and are currently investigating its use in assessment of enamel demineralization.

Esophageal cancer has seen an increase in incidence in recent decades; early intervention is key in improving patient outcomes. As a result screening techniques must be improved in order to detect early cancer and dysplasia endoscopically. Polarized light imaging (PLI) and optical coherence tomography (OCT) are of interest due to their capabilities to probe microstructural tissue properties. In this study healthy and cancerous esophageal tissue samples are imaged with PLI and OCT systems. Classification algorithms are developed to identify polarimetric properties from PLI and Haralick texture features from OCT which are key in distinguishing between the healthy and diseased tissue.

Wide-field Imaging Mueller polarimetry (IMP) is capable to trace the in-plane orientation of brain fiber tracts by detecting the retardance of healthy brain white matter. IMP can help delineating brain tumor during neurosurgery, because tumor cells grow chaotically. However, the underlying crossing fibers may also affect the retardance of healthy brain. We measured with the transmission Mueller microscope two-layered stacks of thin sections of brain corpus callosum tissue. Brain fiber crossing induced the drop in the linear retardance values and azimuth randomization. The depolarization was invariant to mutual orientation of corpus callosum stripes, hence, the studies of brain tumor depolarization may help to distinguish brain tumor from the fiber crossing zones.

Preterm birth (PTB) is a critical global health concern, contributing to over 35% of 3.1 million neonatal deaths annually. PTB is linked to various developmental complications, including neurological disorders, cognitive impairment, and gestational difficulties. Our primary objective in this study is to investigate pregnant cervix remodeling using the Self Validating Mueller Matrix Micro-mesoscope (SAMMM). Departing from conventional methods, our research emphasizes visualizing the entire cervix through large field of view mesoscopic imaging and high-resolution microscopic imaging. By employing SAMMM, we aim to visualize the extracellular matrix (ECM) structure in spatially defined cervical sections, from the internal os to the distal cervix, at different gestational stages in mice. This research has significant potential to improve PTB risk assessment and maternal-neonatal healthcare outcomes on a global scale, contributing to enhanced understanding and targeted interventions for better maternal and neonatal health.

The uterine cervix undergoes extensive remodeling during pregnancy to facilitate successful childbirth. The extracellular matrix (ECM) plays a pivotal role in this remodeling process, affecting cervical biomechanics and its ability to maintain structural integrity throughout gestation. However, early softening of the uterine cervix due to accelerated remodeling of the cervix ECM leads to Preterm Birth. In this study, we performed Mueller matrix polarization imaging of mice cervix at different pregnancy time points and analyzed polarization parameters to assess the associated cervical collagen remodeling. Our research focuses on the depth-resolved Mueller matrix polarization assessment of the ECM structure evolution of mice cervix sections, spanning from external OS to the internal OS of the cervical region, at different gestation stages. Our statistical analysis of the MM results yields valuable information on the variation in the micro-structural organization of the cervical ECM across depths.

Mueller matrix describes the polarization properties of the samples comprehensively, characterizing microstructural information at subcellular-level. Mueller matrix microscopy is a promising non-invasive tool for pathological diagnosis, but it can be challenging to extract polarization parameters that correlate with pathological variation. In this study, we propose a polarization super-pixel based polarization feature extraction framework. Polarization super-pixels are able to represent the polarization features of the biological sample in a simple, compact, and comprehensive way, while reducing the data volume drastically. Using various pathological samples including breast cancer, liver cancer, and lung cancer, we show that polarization super-pixel approach greatly increases the efficiency and performance of the downstream supervised and unsupervised learning tasks, for cancerous tissue identification and microstructural composition analysis. We also propose the super-pixel based label spreading method, which iteratively propagates pathologist’s initial manual label of cancerous region to the entire field of view, highlighting the tissues with the same microstructural features.

We introduce a spectral domain polarization sensitive optical coherence tomography system with balanced detection capability. The design relies on polarization optics to split incoming light into reference and sample paths. Modified light returning from these paths creates the co- and cross-polarization channels, which are respectively coupled into two polarization-maintaining fibers. These fibers carry the light to a custom spectrometer, and their orthogonal axes help form the interference. The spectrometer produces two pairs of highly aligned and focused spectral lines on a camera for optimal balanced detection operation. System performance is characterized and demonstrated for biomedical imaging with improved signal-to-noise ratio.

Several promising applications of terahertz spectroscopy and imaging techniques in biological and medical diagnostics have been investigated over the years. Polarimetric systems are useful for enhancing imaging contrasts, yet the interplay between THz polarization and the discrete structures in biological samples is still obscure. In this work, we performed Monte Carlo simulations of the propagation of the THz waves in tissues with intrinsic random structures. The polarization states of backscattered THz radiation are obtained for different conditions and their connections are analyzed. This approach can be used to guide the design of the imaging modality and the interpretation of data in future THz applications.

Polarization aberrations, such as diattenuation, can significantly affect the performance of modern polarization imaging systems. Polarization adaptive optics (P-AO) provides a means for compensating polarization aberrations, although an approach to deal with diattenuation is not yet available. In this work, we theoretically investigate the potential of a P-AO-assisted diattenuation aberrated Stokes vector measurement system. We provide a comprehensive theoretical and quantitative analysis of the properties regarding diattenuation aberration that can be compensated by P-AO to ensure the optimal performance of a Stokes vector sensing/imaging system. This work provides a solid basis for future use of P-AO in aberrated polarimetric applications.