Three-dimensional (3D) refractive index (RI) tomography has recently become an exciting new tool for biological studies. However, its limitation to (1) thin samples resulting from a need of transmissive illumination and (2) small fields of view (typically ${\sim}50 \;{\unicode{x00B5}{\rm m}} \times 50 \;{\unicode{x00B5}{\rm m}}$) has hindered its utility in broader biomedical applications. In this work, we demonstrate 3D RI tomography with a large field of view in opaque, arbitrarily thick scattering samples (unsuitable for imaging with conventional transmissive tomographic techniques) with a penetration depth of ca. one mean free scattering path length (${\sim}100 \;{\unicode{x00B5}{\rm m}}$ in tissue) using a simple, low-cost microscope system with epi-illumination. This approach leverages a solution to the inverse scattering problem via the general non-paraxial 3D optical transfer function of our quantitative oblique back-illumination microscopy (qOBM) optical system. A theoretical analysis is presented along with simulations and experimental validations using polystyrene beads, and rat and human thick brain tissues. This work has significant implications for the investigation of optically thick, semi-infinite samples in a non-invasive and label-free manner. This unique 3D qOBM approach can extend the utility of 3D RI tomography for translational and clinical medicine.

中文翻译：

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外延模式下不透明样品的定量 3D 折射率断层扫描

三维 (3D) 折射率 (RI) 断层扫描最近已成为令人兴奋的生物研究新工具。然而，它的局限性在于（1）由于需要透射照明而导致的薄样本和（2）小视野（通常为 ${\sim}50 \;{\unicode{x00B5}{\rm m}} \times 50 \;{\unicode{x00B5}{\rm m}}$ ) 阻碍了其在更广泛的生物医学应用中的实用性。在这项工作中，我们展示了具有大视野的 3D RI 断层扫描，在不透明、任意厚的散射样本（不适合使用传统透射断层扫描技术成像）中，穿透深度约为 一个平均自由散射路径长度 ( ${\sim}100 \;{\unicode{x00B5}{\rm m}}$在组织中）使用带有落射照明的简单、低成本的显微镜系统。这种方法通过我们的定量斜背照明显微镜 (qOBM) 光学系统的一般非近轴 3D 光学传递函数来利用逆散射问题的解决方案。提出了理论分析以及使用聚苯乙烯珠、大鼠和人类厚脑组织的模拟和实验验证。这项工作对以非侵入性和无标记方式研究光学厚、半无限样品具有重要意义。这种独特的 3D qOBM 方法可以扩展 3D RI 断层扫描在转化医学和临床医学中的应用。