采用高精度纳米位移台作为被测振动体目标,研究基于超小自聚焦(GRIN)光纤探头的扫频光学相干层析成像(SS-OCT)测振技术。解析基于超小GRIN光纤探头的集成化SS-OCT工作性能,理论上该系统可测振动的最大峰峰值达12.5 mm,最大频率达25 kHz。搭建相应的测振实验系统,并进行微小振动的测试及分析。结果显示,设置纳米位移台振动峰峰值范围1 nm~5 μm、频率范围1~200 Hz,该集成化SS-OCT测振系统可测出频率1 Hz、峰峰值6 nm及以上的微小振动。对振幅为25 nm、频率为10Hz的单频正弦振动信号,系统的重复性实验标准偏差为0.003。结果表明,基于超小GRIN光纤探头的集成化SS-OCT系统具有测量微小振动的可行性,为进一步研究其在微小振动和位移等精确测量领域的应用提供了实验基础。

Cerebral edema is a severe complication of acute ischemic stroke with high mortality but limited treatment. Although parameters such as brain water content and intracranial pressure may represent the global assessment of edema, optical properties can appear heterogeneously throughout the cerebral tissue relative to the site of injury. In this study, we have monitored the edema formation and progression in both permanent and transient middle cerebral artery occlusion models in rats. Edema was reflected by the decrease of optical attenuation coefficient (OAC) value in OCT system. By utilizing swept-source optical coherence tomography (SS-OCT), we found that in photochemically induced permanent focal stroke model, both the edema size and edema index, steadily developed until the end of monitor (7 h). Comparatively, when transient ischemia was introduced with endothelin-1 (ET-1), the edema was detected as early as 15 min, and began to recover after 30 min until monitor was finished (3 h). Despite the majority of the edema being recovered to some extent, the condition of a small region within the edema kept deteriorating, presumably due to the reperfusion damage which might result in serious clinical outcomes. Our study has compared the edema characteristics from two different acute ischemic stroke situations. This work not only confirms the capability of OCT to temporal and spatial monitor of edema but is also able to locate focal conditions at some areas that might highly determine the prognosis and treatment decisions.

Accurate segmentation of choroidal thickness (CT) and vasculature is important to better analyze and understand the choroid-related ocular diseases. In this paper, we proposed and implemented a novel and practical method based on the deep learning algorithms, residual U-Net, to segment and quantify the CT and vasculature automatically. With limited training data and validation data, the residual U-Net was capable of identifying the choroidal boundaries as precise as the manual segmentation compared with an experienced operator. Then, the trained deep learning algorithms was applied to 217 images and six choroidal relevant parameters were extracted, we found high intraclass correlation coefficients (ICC) of more than 0.964 between manual and automatic segmentation methods. The automatic method also achieved great reproducibility with ICC greater than 0.913, indicating good consistency of the automatic segmentation method. Our results suggested the deep learning algorithms can accurately and efficiently segment choroid boundaries, which will be helpful to quantify the CT and vasculature.

基于半导体光放大器和高速光纤法布里-珀罗滤波器,搭建了一个用于产生高速扫频激光的短环形腔。滤波器从长波到短波扫描时,关闭半导体光放大器的偏置电流,可以获得50%占空比的扫频激光。借助交织器,可以获得占空比为100%的扫频激光。再利用二级半导体光放大器,可以进一步提高扫频激光的输出功率。经测试,本扫频激光的扫描频率为500 kHz,中心波长为1550 nm,扫描范围达到67 nm,有效相干长度为6.5 mm,平均输出功率大于20 mW。

扫频光源是扫频光学相干层析(SSOCT)的关键器件。高质量的扫频光源可以提高系统的成像速度、分辨率和信噪比。该文采用光纤声光可调滤光器(FAOTF)、保偏半导体光放大器(PMBOA)、光纤隔离器和光纤耦合器搭建了环形腔结构的扫频光源, 实验得到一种全光纤扫频光源,其扫频速率为100 kHz, 扫频范围为119 nm(1 550.146 2~1 619.470 0 nm), 单光谱3 dB带宽可达0.096 6 nm, 平均输出功率12 mW。该扫频光源具有扫频范围广、速度快、相干性好等优点, 在SSOCT系统中具有一定的实用价值。

利用随机相矢量和模型,描述了光学相干层析术(OCT)结构信号的强度概率密度分布,推导出振幅差分信号的概率密度分布,从理论上确定了差分图像的动态与静态区域的阈值模型。利用一套可对人体皮肤的微血管进行扫描成像的扫频光学相干层析系统,通过阈值模型生成二值化图像,将实验室已有的基于体数据的互相关图像与二值化图像相结合。结果表明该模型有助于减小图像的散斑噪声,从而获得更清晰的结构信息。

为了制作高速扫频光源,基于光纤法布里-珀罗可调滤波器和半导体光放大器搭建了一个短环形腔。首先,通过半导体光放大器的通断电控制,实现占空比为50%的扫频激光输出。然后,利用交织器把激光分成两路再进行错位叠加,从而获得占空比为100%、扫描频率为可调滤波器振动频率两倍的扫频激光。最后,扫频激光经过二级半导体光放大器进行再放大,实现更高功率的扫频输出。所获得的扫频激光,扫描频率为245 kHz,中心波长约为1544 nm,扫描范围达到73 nm,有效相干长度为12 mm,平均输出功率大于20 mW。本文采用的设计方案对于制备高性能、低成本的高速扫频光源具有重要的实用意义。

当前墨迹伪造造成的经济损失逐年增加,基于此,提出一种基于扫频光学相干层析(SSOCT)的墨迹鉴别方法。使用自主搭建的SSOCT成像系统采集墨迹样品背向反射光强随深度下降的数据,通过数据拟合获得墨迹层的衰减系数,用以区分同种颜色不同品牌墨水在白纸上书写的墨迹。实验测得百乐牌墨迹衰减系数范围为0.1333~0.1434,得力牌墨迹衰减系数范围为0.1501~0.1695,英雄牌墨迹衰减系数范围为0.1748~0.1892。重建了使用三种墨水书写的“OCT”字母的X-Y横截面图像,实现了墨迹的鉴别与区分,验证了方法的可行性。