Optical sensors for ultrasound detection in photoacoustic imaging

光声学(PA)是生物医学成像的一种形式，它结合了超声波和光学成像的优点。将高强度激光脉冲传输到生物组织中允许在组织内有效地产生超声，从而可以以常规光学手段无法获得的方式对其进行成像。然而，目前在激光光源和超声波检测方面的技术限制限制了PA在实验室以外的使用。 该项目的目标包括(1)制造超灵敏的大带宽超声/PA传感器并将其集成到多传感器阵列中；(2)创建可用于临床环境的紧凑型PA光源；以及(3)使用这些阵列来研究生物系统中的新现象。 目标1本身就是一项重大的技术进步。更低的可探测压力和更高的动态范围将使我们能够从生物组织内部更深的地方重建图像，而更高的带宽将提高图像的分辨率。同时，我们还将致力于这些微型超声波传感器的阵列，在硅光子学代工厂的帮助下形成低成本的多元素阵列，例如AIM(美国制造学会)集成光子学倡议。 AIM 2将克服传统光声源的繁琐和局限性，传统的光声源是一种体积庞大的激光器，只能以低于100赫兹的重复频率发射脉冲。我们将开发具有紧凑型高功率激光二极管的便携式光声成像系统，利用正在进行的努力，为无人驾驶汽车的LIDAR系统增加脉冲激光二极管的功率。传感器灵敏度的提高将进一步使人们能够使用更低成本、更低功率的激光器来诱导PA信号，从而使激光器更安全。 总而言之，我们的传感器开发和系统优化将减少PA成像的尺寸和成本，并将提供一种足够用于大规模药理学研究和世界各地许多实验室临床前研究的有用和廉价的工具。 AIM 3将开发多模式深层组织PA成像的新技术，这将导致一种非侵入性床边成像方法。该方法将实时提供组织中新陈代谢和血流变化的地图。此外，多模式PA成像性能可以大大受益于快速激光二极管为基础的灵活光源，正如我们之前对大脑的全光学显微镜研究中所显示的那样。 加拿大在开发先进的医学成像技术方面处于领先地位，在多伦多设有技术研究所等中心，负责开发和利用成像技术以改善健康。像Fujifilm Visualsonics Inc.这样的超声波和光声成像领域的知识用户可以将我们的发现转化为世界各地药物开发和医学成像的新机会。

Photoacoustics (PA) is a form of biomedical imaging that combines the benefits of both ultrasound and optical imaging. The delivery of high intensity laser pulses into biological tissue allows for the efficient generation of ultrasound in-tissue so that it can be imaged in a way that would otherwise be inaccessible with conventional optical means. However, current technological restrictions, in both the laser source and ultrasound detection, limit the use of PA beyond the lab setting. The aims of this project include (1) the fabrication of an ultrasensitive large-bandwidth ultrasound/PA sensor and incorporating it into a multi-sensor array, (2) creating a compact PA optical source that can be used in the clinical setting, and (3) using these arrays to investigate new phenomena in biological systems. Aim 1 is a major technological advance in itself. The lower detectable pressures and improved dynamic range will allow us to reconstruct images from deeper inside biological tissue, and the higher bandwidth will improve the resolution of the images. In parallel, we will also be working on an array of these miniature ultrasound sensors, leading to a low-cost multi-element array with the help of a silicon photonics foundry such as the AIM (American Institute of Manufacturing) Integrated Photonics Initiative. Aim 2 will overcome the cumbersome and limiting properties of the conventional photoacoustic source a bulky laser that can only deliver pulses at repetition rates of less than 100 Hz. We will develop portable photo-acoustic imaging systems with compact high power laser diodes, leveraging ongoing efforts to increase power in pulsed laser diodes for LIDAR systems in driver-less cars. Improving sensor sensitivity will further enable the use of lower cost, lower power and, consequently, safer lasers for inducing the PA signal. Together, our sensor development and system optimization will reduce the size and cost of PA imaging and will provide a tool that is useful and inexpensive enough for use in large-scale pharmacological studies, and in many labs worldwide in preclinical studies. Aim 3 will develop new techniques in multi-modal deep tissue PA imaging that will lead to a non-invasive bedside imaging method. The method will provide simultaneously maps of metabolic and blood flow changes in the tissue in real time. Further, multi-modal PA imaging performance can greatly benefit from a fast laser diode-based agile light source as we showed in our previous all-optical microscopy studies of the brain. Canada is a leader in developing advanced medical imaging technologies, with centers in Toronto such as the Techna Institute responsible for the development and exploitation of imaging technology for improved health. Knowledge users in ultrasound and photoacoustic imaging such as FUJIFILM VisualSonics Inc. can translate our discoveries to new opportunities in drug development and medical imaging worldwide.