Cannon Taylor M, Bouma Brett E, Uribe-Patarroyo Néstor
Massachusetts Institute of Technology, Institute of Medical Engineering and Science, 70 Massachusetts Avenue, Cambridge, MA 02141, USA.
Wellman Center for Photomedicine, Massachusetts General Hospital, 40 Blossom St, Boston, MA 02114, USA.
Biomed Opt Express. 2023 Jul 27;14(8):4326-4348. doi: 10.1364/BOE.494518. eCollection 2023 Aug 1.
Optical coherence tomography (OCT) leverages light scattering by biological tissues as endogenous contrast to form structural images. Light scattering behavior is dictated by the optical properties of the tissue, which depend on microstructural details at the cellular or sub-cellular level. Methods to measure these properties from OCT intensity data have been explored in the context of a number of biomedical applications seeking to access this sub-resolution tissue microstructure and thereby increase the diagnostic impact of OCT. Most commonly, the optical attenuation coefficient, an analogue of the scattering coefficient, has been used as a surrogate metric linking OCT intensity to subcellular particle characteristics. To record attenuation coefficient data that is accurately representative of the underlying physical properties of a given sample, it is necessary to account for the impact of the OCT imaging system itself on the distribution of light intensity in the sample, including the numerical aperture (NA) of the system and the location of the focal plane with respect to the sample surface, as well as the potential contribution of multiple scattering to the reconstructed intensity signal. Although these considerations complicate attenuation coefficient measurement and interpretation, a suitably calibrated system may potentiate a powerful strategy for gaining additional information about the scattering behavior and microstructure of samples. In this work, we experimentally show that altering the OCT system geometry minimally impacts measured attenuation coefficients in samples presumed to be singly scattering, but changes these measurements in more highly scattering samples. Using both depth-resolved attenuation coefficient data and layer-resolved backscattering coefficients, we demonstrate the retrieval of scattering particle diameter and concentration in tissue-mimicking phantoms, and the impact of presumed multiple scattering on these calculations. We further extend our approach to characterize a murine brain tissue sample and highlight a tumor-bearing region based on increased scattering particle density. Through these methods, we not only enhance conventional OCT attenuation coefficient analysis by decoupling the independent effects of particle size and concentration, but also discriminate areas of strong multiple scattering through minor changes to system topology to provide a framework for assessing the accuracy of these measurements.
光学相干断层扫描（OCT）利用生物组织的光散射作为内源性对比度来形成结构图像。光散射行为由组织的光学特性决定，而组织的光学特性又取决于细胞或亚细胞水平的微观结构细节。在许多生物医学应用中，为了获取这种亚分辨率的组织微观结构从而提高OCT的诊断效果，人们已经探索了从OCT强度数据测量这些特性的方法。最常见的是，光学衰减系数（散射系数的类似物）已被用作将OCT强度与亚细胞颗粒特征联系起来的替代指标。为了记录准确代表给定样品潜在物理特性的衰减系数数据，有必要考虑OCT成像系统本身对样品中光强分布的影响，包括系统的数值孔径（NA）以及焦平面相对于样品表面的位置，还有多次散射对重建强度信号的潜在贡献。尽管这些因素使衰减系数的测量和解释变得复杂，但经过适当校准的系统可能会增强一种强大的策略，用于获取有关样品散射行为和微观结构的更多信息。在这项工作中，我们通过实验表明，改变OCT系统几何结构对假定为单次散射的样品中测量的衰减系数影响最小，但会改变在散射更强的样品中的这些测量结果。利用深度分辨的衰减系数数据和层分辨的背向散射系数，我们展示了在仿组织体模中散射颗粒直径和浓度的反演，以及假定的多次散射对这些计算的影响。我们进一步扩展我们的方法来表征小鼠脑组织样本，并基于增加的散射颗粒密度突出显示一个肿瘤区域。通过这些方法，我们不仅通过解耦颗粒大小和浓度的独立影响来增强传统的OCT衰减系数分析，还通过对系统拓扑结构的微小改变来区分强多次散射区域，从而为评估这些测量的准确性提供一个框架。
