光声与光学相干层析双模式成像技术研究
文献类型：学位论文
| 作者 | 潘柳华 |
| 文献子类 | 博士 |
| 导师 | 王向朝 |
| 关键词 | 光声成像 photoacoustic imaging 光学相干层析成像 optical coherence tomography 双模式成像 dual-mode imaging 图像质量 image quality 血液流速测量 blood flow measurement |
| 其他题名 | Study on dual-modal imaging of photoacoustic and optical coherence tomography |
| 英文摘要 | 光声成像（Photoacoustic imaging, PAI）是一种基于光声效应的成像技术，通过探测脉冲激光照射下生物组织内部产生的超声波，实现对生物组织的成像。光声信号强度直接与组织的吸收特性相关，所以PAI是一种基于吸收对比度的成像技术，可实现基于光吸收效应的功能成像。光学相干层析成像（Optical coherence tomography, OCT）是基于生物组织光散射特性的成像技术，通过探测组织的背向散射光，实现组织的层析结构成像，以及基于光散射效应的功能成像。将PAI与OCT结合的光声与光学相干层析双模式成像技术能够同时获得生物组织对光的吸收对比度图像和生物组织的层析结构图像，可全面获取生物组织内部的结构信息和功能信息。然而目前国际上光声/光学相干层析双模式成像技术尚处于研究阶段，实际应用仍存在一些关键技术问题待解决。在结构成像方面，OCT存在色散问题，使其难以满足生物医学对高像质光学成像的需求。在功能成像特别是血液绝对流速测量方面，多普勒OCT只对沿探测光束传播方向流动的血液敏感，而PAI中的光声相关谱法（Photoacoustic correlation spectroscopy, PACS）只能测量垂直于探测光束传播方向的血液流速分量，且PACS测量血液流速时，激发光重复频率、血流方向与探测光束传播方向的夹角等因素对血液流速测量的影响需要进一步研究。本论文针对上述光声/光学相干层析双模式成像中存在的问题，提出了相应的技术方案，并进行了理论分析和实验研究。主要工作包括以下几个方面： 1. 基于搭建的激光扫描型光声显微（photoacoustic microscopy, PAM）系统，利用PACS方法对血液流速进行测量，并研究激发光重复频率、血流方向与探测光束传播方向的夹角对血液流速测量准确性的影响。实验结果表明，在利用PACS方法测量血液流速时，血流速度越快，所需激发光重复频率越高。当血流方向与探测光束传播方向垂直时，通过调节激发光重复频率，得到血液流速的测量范围为 0.059-92.3 mm/s，测量值与真实值的相关系数为0.992。当血流方向与探测光束传播方向不垂直时，血液流速测量值与血液流速实际值的比值与样品倾斜角度呈余弦关系，即PACS方法测得的流速值是垂直于探测光束传播方向的血液流速分量。 2. 提出一种随成像深度变化的色散补偿方法，在全成像深度范围内提高OCT图像的质量。该方法利用迭代算法计算出若干成像深度处的色散补偿系数，通过数值计算，得到色散补偿系数与成像深度的关系表达式，计算出各成像深度处的色散补偿系数，利用这些色散补偿系数消除相应成像深度处信号的高阶色散相位，从而有针对性地对系统中参考臂与样品臂引入的色散失配进行补偿。理论分析和实验研究表明，该方法能够在全成像深度范围内有效提高OCT图像的质量。 3. 提出一种基于光声显微/光学相干层析（PAM/OCT）双模式成像系统的血流绝对速度和角度测量方法。在搭建的PAM/OCT系统中，利用PAM测量垂直于探测光束传播方向的血液流速分量，利用多普勒OCT测量平行于探测光束传播方向的血液流速分量，最终得到血流绝对速度和角度。当改变流速为1 mm/s的血液样品的倾斜角度时，利用该系统测量得到的血流绝对速度的标准差为0.02 mm/s，测量得到的血流角度与实际样品倾斜角度的相关系数为0.997。实验结果表明，PAM/OCT可用于测量血流绝对速度和角度。; Photoacoustic imaging (PAI) is a kind of imaging technique which is based on the photoacoustic effect. When a short pulsed laser irradiates the biological tissue, the biological tissue absorbs the light energy and generates ultrasonic waves. By detecting the ultrasonic waves, PAI provides the light-absorption characteristics of the tissue and can realize the structure imaging and functional imaging. Optical coherence tomography (OCT) is a kind of imaging technique which is based on light scattering. Through detecting the backscattered light from biological tissue, the tomographic image and the functional image based on optical scattering can be obtained. A dual-mode imaging technique which combines photoacoustic imaging and optical coherence tomography (PA/OCT) is presented. PA/OCT obtains the light-absorption contrast image and the tomographic image simultaneously, and provides structure information and functional information of tissue. At present, PA/OCT is still in the research stage and there are some crucial technical problems for the practical application. For the structure imaging, because of the dispersion in OCT, it is difficult to achieve high-quality optical imaging for biomedicine application. For the functional imaging, especially blood flow velocity measurement, Doppler OCT measures the blood flow velocity which is parallel to the direction of incident laser beam. The method of photoacoustic correlation spectroscopy (PACS) based on PAI can only measure the blood flow velocity which is perpendicular to the direction of incident laser beam. In the PACS measurement, the effect of laser repetition rate on the velocity measurement needs to be further studied. The influence of the angle between the laser beam and the vessel on the blood flow velocity measurement also needs to be considered. In view of these problems, several techniques are proposed for enhancing the image quality and measuring the absolute flow velocity. These techniques are validated both theoretically and experimentally.The main contents of this dissertation are as follows. 1. A laser scanning photoacoustic microscopy (PAM) system is developed for measuring blood flow velocity by PACS. The effect of the laser repetition rate on the blood flow velocity measurement is presented. Experimental results show that the higher the blood flow velocity is, the higher the laser repetition rate is required. When the blood flow orientation is perpendicular to the direction of incident laser beam, the measurement range of blood flow velocity is 0.059-92.3 mm/s. The correlation coefficient between the measured flow velocities and the actual flow velocities is 0.992. When the blood flow orientation is not perpendicular to the direction of incident laser beam, the ratio between the measured flow velocity and the original flow velocity is cosine to the tilted angle of sample. It is concluded that PACS method is adopted for the measurement of blood flow velocity which is perpendicular to the direction of incident laser beam. 2. A depth-dependent dispersion compensation algorithm for enhancing the image quality of the Fourier-domain OCT at full imaging depth is presented. The dispersion compensation coefficients at some depths are calculated by an iterative algorithm. Through numerical calculation, a mathematical expression between dispersion compensation coefficient and depth is obtained. Utilizing the mathematical expression, the dispersion compensation coefficients at different depths are calculated to eliminate the high-order dispersion phase at each depth. Then the dispersion between the reference arm and sample arm is compensated. Theoretical analysis and experimental research show that the depth-dependent dispersion compensation algorithm can improve OCT image quality at full imaging depth. 3. A dual-mode imaging system which combines PAM and OCT is presented for measuring absolute blood flow velocity and orientation. In the PAM/OCT, the blood flow velocity which is perpendicular to the direction of the incident laser beam is measured by PACS. The blood flow velocity which is parallel to the direction of the incident laser beam is measured by Doppler OCT. Then the absolute velocity and orientation of blood flow are obtained. For the blood with flow velocity of 1 mm/s at different tilt angles, the standard deviation of the absolute blood flow velocity measured by PAM/OCT is 0.02 mm/s. The correlation coefficient between the measured blood flow orientation and the actual flow orientation is 0.997. The experimental results show that the PAM/OCT is able to measure absolute blood flow velocity and orientation. |
| 学科主题 | 光学工程 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31103]  |
| 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 | 潘柳华. 光声与光学相干层析双模式成像技术研究[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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