Collaborative Research in Biophotonics: Towards high-resolution, label-free molecular imaging in deep tissue via stimulated Raman excitation and ultrasound detection

光学组织成像的巨大挑战是在保持分子特异性和高空间分辨率的同时，能够深入穿透组织。提出的项目通过开发一种基于受激拉曼激发和非线性诱导光声波检测的新型成像模式来解决这一重大挑战。被称为受激拉曼光声显微镜，提出的模式结合了化学特异性，通过分子选择性受激拉曼激发与深穿透和高分辨率光声成像。与现有的自发和非线性拉曼显微成像相比，最大成像深度有望至少延长一个数量级。与现有的光声成像相比，无需借助外部分子标记即可实现所需的分子特异性。这个项目将扩展现有的知识如何先进的光谱工具可以成功地用于生物医学成像。它为开发独立的分子成像显微镜奠定了基础，能够在没有外部标签的情况下提供高分辨率的深部组织成像。本研究将探讨受激拉曼激发下光声产生的机理。研究的重点是组织中的弹性散射如何影响所提出的成像模式。蒙特卡罗模拟将模拟双波长、短脉冲光在散射介质中的传播效应。这些结果将指导设计最佳的光学照明几何形状在未来的原型提出的显微镜。定量实验研究将在理论估计和蒙特卡罗模拟的指导下进行。通过匹配信号带宽和采用新型超声探测器，可以提高光声探测的灵敏度。在非散射介质中，受激拉曼光声探测的灵敏度将在存在背景线性光学吸收的情况下进行实验量化，其影响将通过波长和/或延时调制来减轻。

1066776/1066562Zhang/YakovlevThe grand challenge of optical tissue imaging is the ability to penetrate deeply into tissue while preserving molecular specificity and high spatial resolution. The proposed project tackles this grand challenge by developing a novel imaging modality based on stimulated Raman excitation and detection of the nonlinearly induced photoacoustic waves. Referred to as stimulated Raman photoacoustic microscopy, the proposed modality combines chemical specificity through the molecularly selective stimulated Raman excitation with the deep penetration and high-resolution photoacoustic imaging. Compared with existing spontaneous and nonlinear Raman microscopic imaging, the maximum imaging depth is expected to be extended by at least one order of magnitude. Compared with existing photoacoustic imaging, the much needed molecular specificity is achieved without resorting to extrinsic molecular labeling.This project will extend the existing knowledge on how advanced spectroscopic tools can be successfully used for biomedical imaging. It lays the foundation to develop a stand-alone molecular imaging microscope, capable of providing high-resolution deep tissue imaging without external labels. In the proposed research, the mechanism of the photoacoustic generation under the stimulated Raman excitation will be investigated. The investigations focus on how the elastic scattering in tissue will affect the proposed imaging modality. Monte Carlo simulations will model the effect of dual wavelength, short-pulse light propagation in scattering medium. These results will direct the design of the optimal optical illumination geometry in the future prototyping of the proposed microscope. Quantitative experimental studies will be carried out following the guidance of the theoretical estimation and Monte Carlo simulation. The sensitivity of the photoacoustic detection will be improved by matching the signal bandwidth and employing novel ultrasonic detectors. In non-scattering media, the sensitivity of stimulated Raman photoacoustic detection will be experimentally quantified in the presence of background linear optical absorption, whose effect will be mitigated by wavelength and/or time-delay modulation.