Serial sectioning PSOCT and 2PM for imaging post-mortem human brain and neurodegeneration

The study of aging and neurodegenerative processes in the human brain necessitates a comprehensive understanding of its myeloarchitectonic, cytoarchitectonic, and vascular structures. While recent computational advances have enabled volumetric reconstruction of the human brain using stained slices, the standard histological processing methods have often led to tissue distortions and loss, making deformation-free reconstruction challenging. Therefore, the development of a multi-scale and volumetric imaging technique that can accurately measure multiple structures within the intact brain would be a significant technical breakthrough. In this work, we present the development of an integrated approach that combines serial sectioning Polarization Sensitive Optical Coherence Tomography (PSOCT) and Two Photon Microscopy (2PM) to provide label-free multi-contrast imaging of human brain tissue. Our method allows for the simultaneous visualization of scattering, birefringence, and autofluorescence properties of the post-mortem human brain. By utilizing high-throughput reconstruction of 4x4x2cm3 sample blocks and simple registration of PSOCT and 2PM images, we enable comprehensive analysis of myelin content, cellular information, and vascular structure. PSOCT provides mesoscopic images and enables quantitative measurement of those brain structures, while 2PM provide complementary microscopic validation and enrichment of cellular and capillary information. This combined approach reveals myelin density and structure maps of the whole brain block and supplies intricate vessel and capillary networks as well as lipofuscin-filled cell soma across cortical regions, providing insights into the myeloarchitectural, cellular and vascular changes associated with neurodegenerative diseases such as Alzheimer's disease (AD) and Chronic Traumatic Encephalopathy (CTE)

Improving the characterization of ex vivo human brain optical properties using high numerical aperture optical coherence tomography by spatially constraining the confocal parameters

SIGNIFICANCE: The optical properties of biological samples provide information about the structural characteristics of the tissue and any changes arising from pathological conditions. Optical coherence tomography (OCT) has proven to be capable of extracting tissue's optical properties using a model that combines the exponential decay due to tissue scattering and the axial point spread function that arises from the confocal nature of the detection system, particularly for higher numerical aperture (NA) measurements. A weakness in estimating the optical properties is the inter-parameter cross-talk between tissue scattering and the confocal parameters defined by the Rayleigh range and the focus depth. AIM: In this study, we develop a systematic method to improve the characterization of optical properties with high-NA OCT. APPROACH: We developed a method that spatially parameterizes the confocal parameters in a previously established model for estimating the optical properties from the depth profiles of high-NA OCT. RESULTS: The proposed parametrization model was first evaluated on a set of intralipid phantoms and then validated using a low-NA objective in which cross-talk from the confocal parameters is negligible. We then utilize our spatially parameterized model to characterize optical property changes introduced by a tissue index matching process using a simple immersion agent, 2,2'-thiodiethonal. CONCLUSIONS: Our approach improves the confidence of parameter estimation by reducing the degrees of freedom in the non-linear fitting model.Published versio