Ultra-fast Scalable OCT Systems based on a New Photon Detector

成像速度较快的光学相干层析成像(OCT)系统具有显著的诊断价值， 因为它们扩大了视野，缩短了测量时间，提高了分辨率，向下延伸到蜂窝 通过减少运动伪影和支持功能成像(如OCT血管成像)来达到更高的水平。因此， 在不增加更高成本负担的情况下提高成像速度是 下一代OCT系统。而A扫描率超过数十MHz的超高速OCT系统 已经证明，这类系统广泛临床应用的一个主要障碍是它们的显著 由于他们对超快激光和探测器的依赖，他们的成本很高。 并行SS-OCT系统长期以来一直被认为是降低超高速OCT成本的最佳解决方案 系统，因为激光扫描速率和探测器带宽都可以通过增加 并行通道。然而，实现高灵敏度的平衡检测的需要限制了 多个并行通道到少数几个，使这样的系统缺乏吸引力。主要的限制是 平衡检测，这需要严格的容差以使每个探测器的功率均衡 一对。此外，在这种方法中实现散粒噪声限制的灵敏度需要每个探测器有很大的参考功率 随着频道数量的增加，这可能会增加到令人望而却步的激光功率。 莫塞尼的研究小组最近发表了基于一种名为电子注入(EI)的新探测器的结果 结果表明，在没有首次平衡检测的情况下，散粒噪声的极限灵敏度可以达到~105dB 时间到了。此外，散粒噪声限制性能所需的参考功率约为 比传统探测器的震级要低。基于这些发现，这个项目假设一个 利用新的EI探测器可以制作具有散粒噪声受限灵敏度的并行SS-OCT系统；并且 并行OCT具有高度的可扩展性，只需添加低速即可扩展到多MHz扫描速率 并使用传统的低速扫频源。这一假设将在 具体组织了以下几个方面的实验：(1)建立了16路并行OCT系统 基于EI探测器的通道，并在散粒噪声受限灵敏度下运行。(2)扩大系统规模 到并行通道，每个通道以100兆赫兹运行，导致每秒320万次A扫描，同时使用 传统扫描源的扫描频率为50 kHz，只需要几兆瓦的激光功率。 如果这项探索性研究达到计划目标，它将为低成本超高速OCT 系统和OCT系统的扫描速度可能是前所未有的。团队成员已经 过去制作了数千种元素的大型EI探测器阵列，并熟悉工业 和临床局限性。如果成功，该项目将实现并行SS-OCT，在 未来，并且前所未有的速度接近100千兆体素/秒。

Optical coherence tomography (OCT) systems with higher imaging speed have a significant diagnostic value, since they allow increased field of view, reduced measurement time, improved resolution down to the cellular level by reducing motion artifacts, and supporting functional imaging such as OCT angiography. Therefore, increasing the imaging speed without increasing the burden of higher costs is one of the ultimate goals of the next generation OCT systems. While ultra-fast OCT systems with A-scan rates exceeding tens of MHz have been demonstrated, a major roadblock in widespread clinical application of such systems is their significant cost due to their reliance on ultra-fast lasers and detectors. Parallel SS-OCT systems have long been considered the best solution to reduce the cost of ultra-fast OCT systems, since both the laser swept rate and detector bandwidth can be scaled down by increasing the number of parallel channels. However, the need for balanced detection for achieving high sensitivity has limited the number of parallel channels to a handful, and rendering such systems unattractive. The main limitation is the balanced detection, which requires stringent tolerances for the equalization of the power across each detector pair. Also, achieving shot-noise limited sensitivity in this method requires a large reference power per detector that could add up, as the number of channels grows, to a prohibitively large laser power. Mohseni's research group recently published results based on a new detector called Electron Injection (EI) showed that shot-noise limited sensitivity of ~105 dB could be achieved without balanced detection for the first time. Additionally, the required reference power for shot-noise limited performance was about three orders of magnitude lower than the conventional detectors. Based on these findings, this project hypothesize that a parallel SS-OCT system with shot-noise limited sensitivity can be made using the new EI detector; and that the parallel OCT is highly scalable and can be augmented to Multi-MHz scan rate by simply adding low-speed channels and using a conventional low-speed swept source. This hypothesis will be addressed in the experiments organized in the following Specific Aims: (1) to build a parallel OCT system with 16 parallel channels based on EI detectors, and operating at the shot-noise limited sensitivity. (2) to scale up the system to 64 parallel channels, each operating at 100 MHz, leading to 3.2 Mega A-scans per second, while using a conventional swept-source at 50 KHz swept rate and requiring only a few mW of laser power. Should this exploratory study achieve the planned goals, it paves the way for both low-cost ultra-fast OCT systems and also OCT systems with potentially unprecedented scanning speeds. The team members have made large arrays of EI detectors with thousands of elements in the past and are familiar with the industrial and clinical limitations. If success, this project enables parallel SS-OCT with over 1000 parallel channels in the future, and unprecedented speeds approaching 100 Giga-voxels/second.