Multiscale label-free imaging of myelin in human brain tissue with polarization-sensitive optical coherence tomography and birefringence microscopy

Blanke, Nathan; Chang, Shuaibin; Novoseltseva, Anna; Wang, Hui; Boas, David A.; Bigio, Irving J.

doi:10.1364/boe.499354

Cited by 7 publications

(1 citation statement)

References 66 publications

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“…The device was small enough to fit in a surgical cannula. Another work [ 5 ] demonstrated label-free imaging of myelin in a block of human brain tissue using serial-sectioning polarization sensitive optical coherence tomography and quantitative birefringence microscopy. These technologies will aid in understanding the brain’s complex fiber architecture over microscopic to mesoscopic scales.…”

Section: Introductionmentioning

confidence: 99%

Introduction to the Optics and the Brain 2023 feature issue

Bauer,

Gibson,

Wang

et al. 2024

Biomed. Opt. Express

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Section: Introductionmentioning

confidence: 99%

Introduction to the Optics and the Brain 2023 feature issue

Bauer,

Gibson,

Wang

et al. 2024

Biomed. Opt. Express

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Imaging of developing human brains with ex vivo PSOCT and dMRI

Wang,

Blanke,

Gong

et al. 2024

Preprint

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The human brain undergoes substantial developmental changes in the first five years of life. Particularly in the white matter, myelination of axons occurs near birth and continues at a rapid pace during the first 2 to 3 years. Diffusion MRI (dMRI) has revolutionized our understanding of developmental trajectories in white matter. However, the mm-resolution of in vivo techniques bears significant limitation in revealing the microstructure of the developing brain. Polarization sensitive optical coherence tomography (PSOCT) is a three-dimensional (3D) optical imaging technique that uses polarized light interferometry to target myelinated fiber tracts with micrometer resolution. Previous studies have shown that PSOCT contributes significantly to the elucidation of myelin content and quantification of fiber orientation in adult human brains. In this study, we utilized the PSOCT technique to study developing brains during the first 5 years of life in combination with ex vivo dMRI. The results showed that the optical properties of PSOCT quantitatively reveal the myelination process in young children. The imaging contrast of the optic axis orientation is a sensitive measure of fiber orientations in largely unmyelinated brains as young as 3-months-old. The micrometer resolution of PSOCT provides substantially enriched information about complex fiber networks and complements submillimeter dMRI. This new optical tool offers great potential to reveal the white matter structures in normal neurodevelopment and developmental disorders in unprecedented detail.

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Practical considerations for birefringence microscopy of myelin structure: Microscope design and tissue processing for effective imaging

Blanke,

Gray,

Robinson

et al. 2024

Imaging Neuroscience

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Despite the interest in studying and quantifying the structural integrity of myelin in postmortem brain tissue, current methods for high-resolution imaging of myelin with optical microscopy are not sufficient. While imaging methods must have adequate resolution and sensitivity to detect microstructural alterations to myelin that are relevant in aging and neurodegenerative disease, an equally critical aspect is to minimize myelin damage that is induced during tissue processing steps. Birefringence microscopy (BRM) is a powerful technique that leverages the structural anisotropy of myelin to provide detailed, label-free images of myelin at any diffraction-limited optical resolution, while maintaining a simple and low-cost setup. Building on our previous work, we have developed a new BRM system and image processing pipeline that enable efficient, high-throughput imaging of myelin structure at multiple scales. Here, we utilize this system to systematically assess the damage to myelin that is induced by several common tissue processing steps in brain sections from the rhesus monkey. Images taken of the same myelinated axons, before and after each tissue processing step, provide direct evidence that mishandling of tissue during sample preparation can cause significant structural alterations to myelin. First, we report on key advancements to our BRM system, imaging procedure, and image processing pipeline, which provide significant increases to the speed and efficiency of BRM. These include integrating fast piezoelectric rotational stages, minimizing the number of images required (to three images) for determining birefringence parameter maps, and implementing an analytical solution for directly determining birefringence parameter maps. Second, using this BRM system, we demonstrate that effective myelin imaging requires (1) the avoidance of prolonged drying or dehydration of tissue, (2) the selection of the optimal mounting medium (85% glycerol), (3) the avoidance of tissue permeabilization with detergents (i.e., Triton X-100 and Saponin), and (4) the selection of a suitable tissue-section thickness (15, 30 and 60 µm) based on the region of interest. In addition to serving as a guide for new users interested in imaging myelin, these basic experiments in sample preparation highlight that BRM is very sensitive to changes in the underlying lipid structure of myelin and suggest that optimized BRM can enable new studies of myelin breakdown in disease. In this work, we show that BRM is a leading method for detailed imaging and characterization of myelin, and we provide direct evidence that the structure of myelin is highly sensitive to damage during inadequate preparation of brain tissue for imaging, which has previously not been properly characterized for birefringence imaging of myelin. For the most effective, high-resolution imaging of myelin structure, tissue processing should be kept to a minimum, with sections prevented from dehydration and mounted in 85% glycerol. With proper preservation of myelin structure, BRM provides exquisitely detailed images that facilitate the assessment of myelin pathology associated with injury or disease.

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Multiscale label-free imaging of myelin in human brain tissue with polarization-sensitive optical coherence tomography and birefringence microscopy

Cited by 7 publications

References 66 publications

Introduction to the Optics and the Brain 2023 feature issue

Introduction to the Optics and the Brain 2023 feature issue

Imaging of developing human brains with ex vivo PSOCT and dMRI

Practical considerations for birefringence microscopy of myelin structure: Microscope design and tissue processing for effective imaging

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