Optical sensors for ultrasound detection in photoacoustic imaging

光声学（PA）是生物医学成像的一种形式，它结合了超声和光学成像的优点。将高强度激光脉冲输送到生物组织中，可以有效地在组织中产生超声波，从而可以以传统光学手段无法达到的方式对其进行成像。然而，目前的技术限制，在激光源和超声检测，限制了使用PA超出实验室设置。该项目的目标包括(1)制造超灵敏的大带宽超声/PA传感器并将其整合到多传感器阵列中，(2)创建可用于临床环境的紧凑型PA光源，以及(3)使用这些阵列研究生物系统中的新现象。Aim 1本身就是一项重大的技术进步。较低的可检测压力和改进的动态范围将使我们能够从生物组织内部更深处重建图像，更高的带宽将提高图像的分辨率。与此同时，我们还将研究这些微型超声波传感器的阵列，在硅光子代工厂（如AIM（美国制造协会）集成光子倡议）的帮助下，形成低成本的多元件阵列。Aim 2将克服传统光声源（一种体积庞大的激光器，只能以低于100赫兹的重复频率传递脉冲）的笨重和局限性。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来提高用于无人驾驶汽车激光雷达系统的脉冲激光二极管的功率。提高传感器灵敏度将进一步使使用更低的成本，更低的功率，因此，更安全的激光器感应PA信号。总之，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，并将为大规模药理研究和全球许多实验室的临床前研究提供一种有用且价格低廉的工具。目标3将开发多模态深部组织PA成像的新技术，这将导致一种非侵入性床边成像方法。该方法将同时实时提供组织中代谢和血流变化的地图。此外，正如我们在之前的大脑全光学显微镜研究中所展示的那样，基于快速激光二极管的敏捷光源可以极大地受益于多模态PA成像性能。加拿大在开发先进的医疗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。在超声和光声成像方面的知识使用者，如富士公司，可以将我们的发现转化为全球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.