Photoacoustic Imaging in Optically Diffusive Media Using Structured Illumination

第1部分：浑浊介质内部或后面的物体的光学成像是非常具有挑战性的。多次散射扰乱了物体信息，隐藏了物体的特征。该项目旨在开发和表征一种具有前所未有的空间分辨率的光学散射介质深处成像技术。该方法结合了光声成像（一种利用光和超声波成像组织内吸收结构的新兴模式）和结构照明显微镜（一种通过空间模式化照明来提高成像分辨率的既定方法）。提出了利用光通过散射介质传播时自然出现的光学散斑场的数学和实验技术，以提高光声成像的分辨率，使其接近光学分辨率，甚至深入散射介质。这项提议的研究旨在改变生物医学成像，使医生能够透过生物组织来检测和诊断疾病状态或条件。它还可以实现无损检测应用，例如检测高散射聚合物基复合材料和陶瓷样品中的结构缺陷。跨学科的研究工作将支持应用数学和机械工程的研究生，并提供工程、应用数学和生物学方面的培训。本科生研究人员也将在项目期间获得资助。提出了一项延伸到当地高中的计划，研究结果将纳入新的和现有的本科课程。第二部分：本提案的目的是开发一种实验技术和相关的数学框架，利用随机散斑照明和光声检测在多重散射介质内部和通过多重散射介质成像。目标是在多重散射条件下实现光学分辨率成像。当光通过漫射介质传播时自然出现的斑点图案为放置在散射墙后面的物体提供了结构化的照明。利用聚焦超声换能器检测由这种照明产生的光声信号。盲结构照明光声显微镜（BSIPAM）为浑浊介质成像提供了一种全新的方法，通过利用散射过程本身产生的散斑模式来增强图像分辨率。BSIPAM利用了这样一个事实，即吸收物体在脉冲激光照射下产生的光声信号与物体的光吸收分布和照明模式的乘积成正比。在随机散斑模式的非均匀照明的情况下，照明和物体之间的频率混合将物体的高空间频率编码为可以用超声波换能器检测到的低空间频率光声响应。此外，如果由多个随机散斑模式产生的光声响应被记录下来，那么就有足够的信息来重建具有接近散斑大小的空间分辨率的物体图像。该项目开发了实验技术和重建算法，允许在静态和动态扩散介质中使用BSIPAM概念进行前所未有深度的光学分辨率成像。探讨了使用BSIPAM可以实现的基本分辨率增强，并确定了图像重建算法的性能作为散斑大小，成像几何形状，散斑图案数量，成像深度和信噪比的函数。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Part 1:Optical imaging of objects inside or behind turbid media is exceptionally challenging. Multiple scattering scrambles the object information and hides features from view. This project aims to develop and characterize a technique for imaging deep inside of optically scattering media with unprecedented spatial resolution. The approach combines photoacoustic imaging, an emerging modality that uses light and ultrasound to image absorbing structures within tissue, with structured illumination microscopy, an established means of improving imaging resolution by spatially patterning the illumination. Mathematical and experimental techniques are proposed that exploit the optical speckle field that naturally emerges as light propagates through scattering media to enhance the resolution of photoacoustic imaging such that it approaches optical resolution, even deep within scattering media. The proposed research aims to transform biomedical imaging, allowing physicians to see through biological tissue to detect and diagnose disease states or conditions with exceptional resolution. It also enables nondestructive testing applications such as detecting structural defects in highly scattering polymer matrix composites and ceramic samples. The interdisciplinary research effort will support graduate students in applied mathematics and mechanical engineering and provide training in engineering, applied mathematics, and biology. Undergraduate researchers will also be supported for the duration of the project. An outreach program to a local high school is proposed and the research results will be incorporated into new and existing undergraduate classes.Part 2:The objective of this proposal is to develop an experimental technique and associated mathematical framework to image inside of and through multiply scattering media using random speckle illumination and photoacoustic detection. The goal is to achieve optical resolution imaging in the multiple scattering regime. The speckle patterns that naturally emerge as light propagates through diffuse media provide structured illumination to an object placed behind a scattering wall. The photoacoustic signal produced by such illumination is detected using a focused ultrasound transducer. Blind structured illumination photoacoustic microscopy (BSIPAM) offers a fundamentally new approach to imaging in turbid media, where image resolution is enhanced by making use of speckle patterns that are a result of the scattering process itself. BSIPAM exploits the fact that the photoacoustic signal generated by an absorbing object subjected to pulsed laser illumination is proportional to the product of the object optical absorption distribution and the illumination pattern. In the case of non-uniform illumination by a random speckle pattern, frequency mixing between the illumination and object encodes the high spatial frequencies of the object in a low spatial frequency photoacoustic response that can be detected with an ultrasound transducer. Furthermore, if the photoacoustic response generated by multiple random speckle patterns is recorded then there is sufficient information to reconstruct an image of the object with a spatial resolution approaching the speckle size. This project develops experimental techniques and reconstruction algorithms that allow for optical resolution imaging at unprecedented depths within static and dynamic diffusive media using the BSIPAM concept. The fundamental resolution enhancement that can be achieved using BSIPAM is explored and the performance of image reconstruction algorithms as a function of speckle size, imaging geometry, number of speckle patterns, imaging depth, and signal to noise ratio are determined.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.