扫频光学相干层析成像技术研究
文献类型：学位论文
| 作者 | 王瑄 |
| 文献子类 | 博士 |
| 导师 | 曾爱军 |
| 关键词 | 扫频光学相干层析成像 swept source optical coherence tomography 灵敏度 sensitivity 焦深 depth of focus 波数校准 wavenumber calibration 成像深度范围 imaging depth range |
| 其他题名 | Research on Swept Source Optical Coherence Tomography |
| 英文摘要 | 光学相干层析成像（Optical Coherence Tomography, OCT）是一种探测样品背向散射光的生物医学成像技术，具有非侵入、高分辨率、可在体检测生物组织内部微结构等优点。早期的OCT技术通过机械扫描获得待测样品的层析结构图像，称为时域OCT。为了提高成像速度，研究人员提出了频域OCT技术，分为谱域OCT和扫频OCT。与谱域OCT相比，扫频OCT具有成像速度更快、探测效率更高和灵敏度随深度下降速率更慢等优点，更适合于生物组织的实时成像，已成为OCT方向的研究热点。然而，扫频OCT仍存在探测弱样品信号时灵敏度较低、高斯光束照明导致焦深和横向分辨率相互制约以及光源时钟信号触发时成像深度范围受限等问题，降低了系统成像能力，影响了层析图像质量，限制了应用范围。本论文针对上述问题，围绕如何提高扫频OCT的成像能力开展理论与实验研究，主要包括以下几项工作： 1. 提出一种扫频OCT系统灵敏度增强技术。扫频OCT系统中平衡探测器前耦合器的分束比与理想值存在偏差时，将会在探测的干涉信号中引入直流偏置，减小数据采集卡的可利用动态范围，从而影响系统灵敏度。通过理论分析证明，调节分束比较大端口的输出光能量，并增加参考臂的光能量可以提高系统灵敏度。仿真结果证明了该技术的可行性。灵敏度测量结果表明，该技术可将系统灵敏度提高2.3dB，且具有很好的鲁棒性。 2. 提出一种扫频OCT系统焦深扩展技术。针对在样品臂中采用高斯照明时焦深和横向分辨率相互制约的问题，利用圆环达曼光栅产生无衍射贝塞尔光束代替高斯光束照射样品，扩展了系统焦深。设计并搭建了一套基于贝塞尔光束照明的扫频OCT系统，对3μm微球的悬浮溶液进行成像，测得系统的横向分辨率和有效焦深分别为3.6μm和0.8mm，实验结果表明该技术可有效扩展系统焦深。 3. 提出一种扫频OCT系统成像深度范围增加技术。通过高速采集样品干涉信号以增加每个光谱范围内的采样点数，提高光谱分辨率，从而增加成像深度范围。高速采集的样品干涉信号通常随波数非等间隔分布，利用透明薄片产生光程差为固定值的干涉信号，对样品干涉信号进行波数校准，获得随波数等间隔分布的样品干涉信号。仿体实验结果表明，利用该技术可将系统成像深度范围增加至原来的1.9倍。活体鱼眼实验获得了同时包含眼前节和视网膜的层析结构图像，验证了该技术的有效性。; Optical coherence tomography (OCT) is a promising biomedical imaging modality for detecting backscattered light of the sample. It performs many advantages such as non-invasiveness, high resolution and detecting the internal micro-structure of in vivo biological tissues. Early Time Domain OCT (TDOCT) is performed by mechanically scanning the reference arm. To increase the imaging speed, Fourier Domain OCT (FDOCT) is proposed to directly achieve depth-resolved reconstruction of sample. FDOCT can be divided into two implementations: spectral domain OCT (SDOCT) and swept source OCT (SSOCT). SSOCT has several advantages over SDOCT, including higher imaging speed, lower sensitivity roll-off and longer imaging depth range. Therefore, SSOCT is more suitable for real-time imaging and has been the research hotspot. However, SSOCT suffers from several problems, such as low sensitivity for detecting weak signal, small depth of focus for using the Gaussian beam in the sample arm and limited the imaging depth range for using the trigger signal of swept source. These problems reduce the imaging capability of the system, affect the image quality, and limit the application of SSOCT. In order to solve the problems, several techniques for improving the imaging capability of SSOCT are studied. The main contents of this dissertation are as follows. 1. A technique to improve the sensitivity of SSOCT system is proposed. In SSOCT system, when the splitting ratio of the coupler in front of the balanced detector is not perfectly 50/50, there is residual DC bias in the detected interference signal. The DC bias reduces the available dynamic range of the data acquisition card and affects the sensitivity of the system. The influence of the splitting ratio on the sensitivity is analyzed theoretically. The system sensitivity can be increased by adjusting the ratio and increasing the reference arm’s power. The simulation results demonstrate the feasibility of the technique. The experiments show that the system’s sensitivity can be improved by 2.3dB, and the proposed technique has strong robustness. 2. A technique to extend the depth of focus of SSOCT system is proposed. The depth of focus (DOF) and lateral resolution is mutually constrained when the Gaussian beam is used in the sample arm. A non-diffracting Bessel beam, generated by the Circular Damman Grating (CDG), is used instead of the Gaussian beam in the SSOCT system, and the DOF is extended. A SSOCT system based on Bessel beam illumination is designed and built. Experiments of suspension with 3μm microspheres is conducted, and the measured effective DOF of the system reaches 0.8mm with a high lateral resolution of 3.6μm. The results show that the DOF of system can be effectively extended by the proposed technique. 3. A technique to expand the imaging depth range of SSOCT system is proposed. High-speed acquisition enables more sampling points in each spectrum for sample interference signal, thus expanding the imaging depth range. However, the signal is not uniformly spaced with wavenumber, so it is necessary to perform the wavenumber calibration. It can be realized by introducing an interference signal with a fixed optical path difference. The results of phantom experiment show that the imaging depth range obtained by the technique is 1.9 times greater than that of using the source K-clock trigger method. The living fisheye experiments show that the tomographic structure images of the anterior segment and the retina can be obtained simultaneously, which demonstrates the feasibility of the technique. |
| 学科主题 | 光学工程 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31141]  |
| 专题 | 中国科学院上海光学精密机械研究所 |
| 作者单位 | 中国科学院上海光学精密机械研究所 |
| 推荐引用方式 GB/T 7714 | 王瑄. 扫频光学相干层析成像技术研究[D]. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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