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

1066776/1066562 Zhang/Yakovlev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深入组织的能力。提出的项目通过开发一种基于受激拉曼激发和检测非线性诱导光声波的新型成像模式来应对这一巨大挑战。被称为受激拉曼光声显微镜，该方法通过分子选择性受激拉曼激发结合了化学特异性和深度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，最大成像深度有望延长至少一个数量级。与现有的光声成像相比，不需要求助于外在分子标记就可以获得迫切需要的分子特异性。这个项目将扩展现有的关于如何将先进的光谱工具成功地用于生物医学成像的知识。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层组织成像。在拟议的研究中，将研究受激拉曼激发下的光声产生机制。研究的重点是组织中的弹性散射将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果。这些结果将指导未来所提出的显微镜原型的最佳光学照明几何形状的设计。定量实验研究将在理论估算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的超声探测器，可以提高光声检测的灵敏度。在非散射介质中，受激拉曼光声检测的灵敏度将在实验上被量化，背景线性光吸收的存在将通过波长和/或时延调制来减弱其影响。

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.