This Conference Presentation, “Best Student Paper” was recorded for the Photonics West 2022 On-Demand.

Imaging Mueller polarimetry (IMP) was used in reflection geometry and large field of view configuration for the in-plane visualization of brain fiber tracts by exploring the anisotropy of the refractive index of healthy brain white matter. Our initial studies demonstrated that IMP successfully detects in-plane orientation of fiber tracts on a flat surface of the excised brain specimens. This work, performed ex-vivo on complete fresh calf brains proves the potential of IMP as a technique suitable to detect both presence and orientation of brain fiber tracts in the adverse conditions of complex surface topography and presence of blood.

Alignment of tissue fibers, such as collagen, can be disrupted by some cancers. Mueller matrix polarimetry (MMP) is often correlated to this tissue orientation, as seen in cases such as cervical imaging. However, its bulk assessment of a sample’s polarimetric properties prevents it from distinguishing specific structures at different depths, as there would be in any non-uniform or multilayered sample. Spatial Frequency Domain Imaging (SFDI) is a well-documented technique that can be used to manipulate depth of penetration of an investigating light source through use of different sinusoidal frequency patterns. We have combined the two imaging modalities to investigate and differentiate between anisotropic samples with varied depth-dependent structure and demonstrate its use with various tissue phantoms. We also discuss some issues that arise with the combined methodology.

Radiation concerns preclude the use of fluoroscopy guidance in lumbar puncture procedures performed on pregnant women or other at-risk groups. We have developed an alternative method for guidance based on a simple, unscanned polarization-sensitive optical coherence tomography needle tip probe. Using the porcine spine as a model, we show that the polarization signals returned by the probe allow each layer from the skin to the subarachnoid space to be uniquely identified in situ. Combining these signals with needle-tip tracking using Doppler methods provides real-time anatomical localization of the needle tip.

We present a combination of Mueller matrix measurements (635 nm) of cancerous colon specimens and machine-learning approach. Physical realizability filtering and symmetric decomposition were used to extract polarimetric quantities, used as predictors in machine-learning algorithms. The results were visualized using various depolarization spaces. Principal component analysis was used to extract particular features from the model, logistic regression evaluated predictors with high likelihood for tumor detection, while random forest and support vector machines provided the best results for classification. Hence, polarimetry combined with machine-learning approach may increase the histopathology diagnostic accuracy.

Thin sections of uterine cervices from pregnant mice at day 6 and 18 of 19-days gestation period at different spatial locations along the cervices were studied with imaging Mueller polarimetry (IMP) combined with statistical analysis and multi-curve fit. The results suggest using depolarization and linear retardance images for collagen scoring and identification of cervical collagen changes during pregnancy. One day before delivery the remodeling of extracellular matrix of cervical collagen was detectable at the external cervical os, thus, proving that IMP modality may serve for the preterm birth risk assessment associated with the accelerated remodeling of cervical collagen.

This Conference Presentation, High fidelity polarization-sensitive optical coherence tomography through deep learning, was recorded at SPIE Photonics West 2022 held in San Francisco, California, United States.”

Precancer-to-cancer progression in epithelial tissues is marked by cellular proliferation and nuclear pleomorphism. These transformations have been shown to influence tissue optical properties: (1) tissue turbidity (quantified by the scattering coefficient) and (2) average scatterer size. It is found that backscattered polarized light can assess these properties. We use linear and circular depolarization to generate a predictive response surface where turbid media samples cluster by scatterer size and scattering coefficient. The novel polarimetric ability to noninvasively and simultaneously assess scatterer size and scattering coefficient of tissue-like turbid media may improve upon currently invasive skin cancer tests.

A three-dimensional label-free multi-contrast imaging for ex vivo tissue investigation is presented. Computational refocusing is implemented in a Jones-matrix polarization-sensitive optical coherence tomography (PS-OCT) system to overcome the trade-off between imaging depth and lateral resolution. The application of multiple contrast imaging, including intensity, birefringence, and degree-of-polarization uniformity (DOPU), is demonstrated by phantom, porcine muscle, and zebrafish measurements. Extended imaging depth with enhanced lateral resolution over millimeter is achieved. In tissue imaging we find some altered birefringence and DOPU estimation, whose size and alteration are proportional to defocus amount. This biased estimation can be numerically mitigated after applying computational refocusing.