Abbasi Saad, Bell Kevan, Ecclestone Benjamin, Haji Reza Parsin
PhotoMedicine Labs, Department of Systems Design Engineering, University of Waterloo, Waterloo, Ontario, Canada.
IllumiSonics, Inc., Department of Systems Design Engineering, University of Waterloo, Waterloo, Ontario, Canada.
Quant Imaging Med Surg. 2021 Mar;11(3):1033-1045. doi: 10.21037/qims-20-758.
As photoacoustic (PA) techniques progress towards clinical adoption, providing a high-speed live feedback becomes a high priority. To keep up with the instantaneous optical feedback of conventional light microscopes, PA imaging would need to provide a high-resolution video-rate live feed to the user. However, conventional PA microscopy typically trades resolution, sensitivity and imaging speed when optically scanning due to the difficult opto-acoustic confocal geometry. Here, we employ photoacoustic remote sensing (PARS), an all-optical technique that relies on optical confocal geometry, to provide a high-resolution live display in a reflection-mode PA architecture.
Employing a conventional galvanometer scanner and a 600 KHz pulse repetition rate laser we implement a system capable of acquiring 2.5 frames per second in 2D. To complement this fast scanning optical system, we implement a computationally inexpensive image reconstruction method that is able to render the frames with minimal overhead, providing a live display.
Employing the proposed method, we demonstrate a live feedback with frame rates as high as 2.5 Hz in 2D and also report the first results of 3D imaging with a non-contact label-free reflection-mode technique. The method is validated with phantom studies and imaging. Employing a repetition rate of 600 KHz, a live feed of carbon fibers is realized with a C-scan rate of 2.5 Hz. The imaging resolution was measured to be 1.2 µm, the highest reported for a real-time reflection-mode architecture. The mean and peak SNR were measured to be 44 and 62 dB respectively . 3D visualizations of carbon fiber phantoms and mouse ear microvasculature structure are also demonstrated.
In summary, we present a method that has a small computational overhead for image rendering, resulting in a live display capable of real-time frame rates. We also report the first 3D imaging with a non-contact label-free reflection-mode PA technique. The all-optical confocal geometry required by PARS is significantly easier to implement and maintain than the opto-acoustic geometry of conventional PA microscopy techniques. This results in a system capable of high resolution and sensitivity, imaging at real-time rates. The authors believe this work represents a vital step towards a clinical high-resolution reflection-mode video-rate PA imaging system.
随着光声（PA）技术朝着临床应用方向发展，提供高速实时反馈成为当务之急。为了跟上传统光学显微镜的即时光学反馈，光声成像需要向用户提供高分辨率视频速率的实时图像。然而，由于光声共聚焦几何结构复杂，传统的光声显微镜在光学扫描时通常需要在分辨率、灵敏度和成像速度之间进行权衡。在此，我们采用光声遥感（PARS）技术，这是一种基于光学共聚焦几何结构的全光学技术，用于在反射模式光声架构中提供高分辨率实时显示。
我们使用传统的振镜扫描仪和600 KHz脉冲重复率激光器，实现了一个能够以每秒2.5帧的速度在二维平面采集图像的系统。为了补充这个快速扫描光学系统，我们实现了一种计算成本较低的图像重建方法，该方法能够以最小的开销渲染图像帧，从而实现实时显示。
采用所提出的方法，我们展示了二维平面高达2.5 Hz帧率的实时反馈，并且还报告了使用非接触无标记反射模式技术进行三维成像的首批结果。该方法通过模型研究和成像得到验证。使用600 KHz的重复率，以2.5 Hz的C扫描速率实现了碳纤维的实时成像。测量得到的成像分辨率为1.2 µm，这是实时反射模式架构中所报道的最高分辨率。平均信噪比和峰值信噪比分别测量为44 dB和62 dB。还展示了碳纤维模型和小鼠耳部微血管结构的三维可视化图像。
总之，我们提出了一种在图像渲染方面计算开销较小的方法，从而实现了能够达到实时帧率的实时显示。我们还报告了使用非接触无标记反射模式光声技术进行的首次三维成像。与传统光声显微镜技术的光声几何结构相比，PARS所需的全光学共聚焦几何结构显著更易于实现和维护。这使得该系统能够实现高分辨率和高灵敏度，并以实时速率进行成像。作者认为这项工作代表了朝着临床高分辨率反射模式视频速率光声成像系统迈出的重要一步。
