The vascular network in the human brain is universally involved in physiology and neural activity and the alteration is commonly associated with neurological disorders such as traumatic brain injury, stroke, multiple sclerosis, and Alzheimer’s disease. However, small arterioles, venules, and the capillary networks are beyond the resolution of in vivo MRI and optical microscopy only reveals the vasculature of cortex in small animals. We reported a vascular network reconstruction with an automatic serial sectioning polarization sensitive optical coherence tomography at 3.5 micrometer resolution in ex vivo human brain tissue. Pathological patterns surrounding the vessel walls were revealed as well.
Serial Sectioning Optical Coherence Tomography(serial sectioning OCT) has been widely used to investigate the structural and pathological features of brain samples. OCT is an optical imaging technique that provides both the 3D structure of the tissue as well as the optical properties including the scattering coefficient (μs) and back-scattering coefficient (μb). Serial sectioning OCT allows the reconstruction of distortion-free volumetric images at high contrast and high resolution, which has proven to be useful for the detection of cancerous tissue boundaries, visualizing 3D vascular structures and measuring neuron density. The tissue optical properties extracted from the OCT depth profile has been shown to be related to myelin content and neuron density. However, no quantitative correlation of the tissue optical properties with myelin content and neuron density has been reported. Establishing a quantitative relationship will potentially benefit the segmentation of anatomical layers and the characterization of demyelination and neuron loss, which are related to neurological diseases such as Alzheimer’s and Chronic Traumatic Encephalopathy(CTE). Here, we demonstrate using block-face imaging with optical coherence tomography (OCT) to quantitatively measure myelin content and neuron density in the human brain. By correlating the OCT measurements of tissue optical properties with the ground truth of myelin content and neuron density provided by histology, we found that the scattering coefficient possesses a linear relationship with the myelin content across different regions of the human brain, while the neuron density only slightly modulate the overall tissue scattering properties
The signal of optical coherence tomography (OCT) decays exponentially in depth due to tissue scattering, resulting in indistinct tissue features in three-dimension. Moreover, due to limited light penetration depth, extensive volumetric investigation is usually constrained for large-scale biological samples. By integrating serial sectioning technology with block-face imaging, we establish a volumetric OCT acquisition and reconstruction pipeline that incorporates depth-resolved attenuation coefficient estimation, volumetric stitching and filtering, and feature enhancement visualization. We demonstrate this pipeline on ex vivo human brain volumes of several cubic centimeters with 5 um isotropic resolution.
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.
No current imaging technology allows us to directly and without significant distortion visualize the microscopic and defining anatomical features of the human brain. Ex vivo histological techniques can yield exquisite planar images, but the cutting, mounting and staining that are required components of this type of imaging induce distortions that are different for each slice, introducing cross-slice differences that prohibit true 3D analysis. We are overcoming this issue by utilizing Optical Coherence Tomography (OCT) with the goal to image whole human brain cytoarchitectural and laminar properties with potentially 3.5 µm resolution in block-face without the need for exogenous staining. From the intrinsic scattering contrast of the brain tissue, OCT gives us images that are comparable to Nissl stains, but without the distortions introduced in standard histology as the OCT images are acquired from the block face prior to slicing and thus without the need for subsequent staining and mounting. We have shown that laminar and cytoarchitectural properties of the brain can be characterized with OCT just as well as with Nissl staining. We will present our recent advances to improve the axial resolution while maintaining contrast; improvements afforded by speckle reduction procedures; and efforts to obtain quantitative maps of the optical scattering coefficient, an intrinsic property of the tissue.
Neuroanatomical pathways form the basis for functional activity of brain circuits. In the past, we developed a polarization-sensitive optical coherence tomography with serial scanning to achieve large-scale brain imaging. The system was able to visualize 3D fiber tracts of ~20 um in diameter. To investigate the neuroanatomical pathways at finer scales, we have now built a polarization-maintaining fiber based ultra-high resolution polarization-sensitive optical coherence microscope (PS-OCM) at 1300 nm. The PS-OCM has an axial resolution of 3.5 um in tissue. The detection setup consists of two spectrometers, acquiring spectral interference on orthogonal polarization channels. With a single measurement, the setup generates four contrasts: reflectivity, cross-polarization, retardance and optic axis orientation. To investigate the capability of PS-OCM at different resolutions, we used three microscope objectives that yield lateral resolutions of 6.0 um, 3.4 um and 1.3 um. Blocks of formalin fixed mouse brain and human brain were scanned. The cross-polarization and retardance images clearly depict the neuronal fiber structures, which are comparable with that generated by the maximum projection of volumetric reflectivity data. The optic axis orientation quantifies the in-plane fiber orientation. With the lateral resolution of 1.3 um, the retardance contrast is weak in white matter due to the shallow depth of focus. Overall, the ultra-high resolution PS-OCM provides a new tool to reveal neuroanatomical maps in the brain at cellular resolution.
The cytoarchitecture of the human brain is of great interest in diverse fields: neuroanatomy, neurology, neuroscience, and neuropathology. Traditional histology is a method that has been historically used to assess cell and fiber content in the ex vivo human brain. However, this technique suffers from significant distortions. We used a previously demonstrated optical coherence microscopy technique to image individual neurons in several square millimeters of en-face tissue blocks from layer II of the human entorhinal cortex, over 50 μm in depth. The same slices were then sectioned and stained for Nissl substance. We registered the optical coherence tomography (OCT) images with the corresponding Nissl stained slices using a nonlinear transformation. The neurons were then segmented in both images and we quantified the overlap. We show that OCT images contain information about neurons that is comparable to what can be obtained from Nissl staining, and thus can be used to assess the cytoarchitecture of the ex vivo human brain with minimal distortion. With the future integration of a vibratome into the OCT imaging rig, this technique can be scaled up to obtain undistorted volumetric data of centimeter cube tissue blocks in the near term, and entire human hemispheres in the future.
According to the epoch and place, the artists use the same pigments to paint the faces but change their techniques
and the binders, which modify the visual appearances (color, gloss) of the works of art. Various techniques
(encaustic, tempera, oil, synthetic binder) are investigated on model samples containing the same pigments but
different binders and on a old painting. The influence of the techniques on the visual rendering is investigated
experimentally. Goniophotometry and optical coherent tomography are used to determine the surface state, the
gloss and the surface scattering. The spectrometry in the visible range allows to characterize the bulk scattering
by determining the absorption and scattering coefficients of the pigments according to the binders. A particular
oil technique, the art glaze is also studied on a real painting.
The identification of varnishes may be essential for the choice of the appropriate solvent during their removal by
restorers. This recognition is obtained by UV-fluorescence emission spectroscopy with a quasi-monochromatic UVexcitation.
A new portable instrument has been developed in order to implement non-destructive, contactless and in situ
measurements, providing results in real time.
The method is applied to the analysis of a real ancient painting. The resin-based varnish, the recipe and the state of
degradation of the varnish are deduced in different locations of the painting by comparison with a database of reference
varnishes. Moreover, spectral data are compared with the Fluorescence Lifetime Imaging (FLIM) analysis, performed on
the same painting. Different areas containing the same varnish can then be localized on the whole painting. These results
show that both UV-fluorescence methods are complementary for rapid and in situ analysis of varnishes of an entire work
of art.
Nevertheless, the paint layer beneath the varnish modifies the varnish fluorescence spectrum thus complicating its
recognition. Indeed, the possible fluorescence of the binder of the paint layer or its reflectance spectrum must be taken
into account. A systematic experimental study on fresh and aged model samples made of different varnishes, pigments
and binders is presented in this work. It shows that UV-fluorescence emission spectra and diffuse reflectance spectra
must be coupled to extract the fluorescence of the single varnish. Both spectra can be recorded by the presented
instrument. A new theoretical approach is summarized in order to explain this phenomenon.
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.