Development of non-contact photoacoustic tomography

前言和目的：光声断层扫描（PAT）作为一种检测癌症的方法已经研究了20多年。这个想法是基于这样的原理，即与附近的健康组织相比，在肿瘤中和肿瘤周围存在丰富的血红蛋白，在这些区域中提供更高的光吸收。几个小组已经建造了PAT乳房扫描仪，但都使用笨重的水箱将组织声学耦合到压电探测器。消除水箱具有许多潜在的益处，包括减少扫描时间、更高分辨率的PAT图像、灵活的受试者定位以及由于缺乏与受试者的接触而导致的无菌性。这项工作的目标是开发和优化非接触PAT（ncPAT），以实现这些好处。方法：非接触式PAT使用称为双脉冲电子散斑干涉测量（dpESPI）的全息检测技术，该技术避免使用水箱和压电检测器。使用dpESPI，可以测量由到达表面的光声波引起的纳米级表面位移。几个重要的参数涉及到全息设置的性能，需要进一步的研究范围内的PAT。这些包括参考光路和物体光路之间的角度，全息图的空间和时间采样，表面位移到压力估计的转换，以及最后将dpESPI压力估计重建成代表光学吸收体（肿瘤）的光声图像。研究计划： 我们的5年计划包括首先为dpESPI系统开发COMSOL仿真工具（目标1，第1年）。其次，使用dpESPI系统，我们将测量参考物体角度和位移灵敏度之间的关系，并与模拟结果（目标2，第2年）进行比较。第三，我们将测量视场、空间采样间隔和位移灵敏度之间的关系，并与模拟结果（目标3，第3年）进行比较。第四，我们计划测量探测激光脉冲内时间间隔和脉冲间时间间隔对光声采样特性的影响（目标4，第四年）。最后，我们计划实验性地捕获光声数据使用dpESPI从幻影，重建成3D PAT图像，并比较模拟和类似的数据捕获使用传统的水箱PAT系统与压电探测器（目标5，5年）。资源：所有资源均已到位，包括使用常规PAT设备、dpESPI设备、湿实验室设施和计算资源。研究团队：卡森博士是PAT方面的专家。在过去的3年里，他的团队为ncPAT开发了一个非接触式的基于全息的系统。受训人员将包括一名PDF和一名博士生。结论及意义：这项研究将提高对ncPAT技术的理解，以及如何将其用于最终从人体组织中捕获图像。

Introduction and Objective: Photoacoustic tomography (PAT) has been studied as a method to detect cancer for more than 20 years. The idea is based on the principle that there is an abundance of hemoglobin in and around tumors providing higher optical absorption in these regions compared to nearby healthy tissues. Several groups have constructed PAT breast scanners, but all use a cumbersome water tank to acoustically couple tissues to the piezoelectric detectors. Elimination of the water tank has many potential benefits including reduced scan time, higher resolution PAT images, flexible subject positioning, and sterility due to a lack of contact with the subject. The objective of this work will be to develop and optimize non-contact PAT (ncPAT) to realize these benefits. Approach:  Non-contact PAT uses a holographic detection technique called double-pulse electronic speckle pattern interferometry (dpESPI) that avoids the use of a water tank and piezoelectric detectors. With dpESPI it is possible to measure nanometer scale surface displacements resulting from photoacoustic waves arriving at the surface. Several important parameters relate to the performance of the holographic setup and need further research within the context of PAT. These include the angle between the reference and object light paths, spatial and temporal sampling of the holograms, conversion of surface displacements to pressure estimates, and finally reconstruction of the dpESPI pressure estimates into photoacoustic images representative of optical absorbers (tumours). Research Plan: Our 5-year plan includes first developing a COMSOL simulation tool for a dpESPI system (Aim 1, Year 1). Second, using the dpESPI system, we will measure the relationship between reference-object angle and displacement sensitivity and compare to simulation results (Aim 2, Year 2). Third, we will measure the relationship between field of view, spatial sampling interval and displacement sensitivity and compare to simulation results (Aim 3, Year 3). Fourth, we plan to measure the effect of probe laser intra-pulse time interval and inter-pulse time interval on the characteristics of photoacoustic sampling (Aim 4, Year 4). Last, we plan to experimentally capture photoacoustic data using dpESPI from phantoms, reconstruct into 3D PAT images and compare to simulations and similar data captured using a conventional water tank PAT system with piezoelectric detectors (Aim 5, Year 5). Resources: All resources are in place including access to conventional PAT equipment, dpESPI equipment, wet lab facilities, and computing resources. Research Team: Dr. Carson is an expert in PAT. Over last 3 years, his group has developed a non-contact, holography-based system for ncPAT. Trainees will include one PDF and one PhD student. Conclusion and Significance: This research will result in improved understanding of ncPAT technology and how it can be adapted to ultimately capture images from human tissues.