基于微纳光纤法布里—珀罗干涉仪的生物医学光声成像技术

发布时间：2018-03-30 09:22

本文选题：微纳光纤　切入点：微纳光纤光栅　出处：《暨南大学》2014年博士论文

【摘要】：生物医学工程是一门运用自然科学和工程技术的原理与方法,研究各种生物体特别是人体的结构、功能以及其它生命现象的科学。生物医学成像技术是生物医学工程领域最重要的组成部分之一,通过采用光学显微、磁共振等物理手段,获取人体组织内部的空间光学吸收分布函数,提取人眼无法获取的有用信息,为疾病的早期诊断提供重要依据,对人类健康具有重要意义。其中,光声成像方法是基于光声效应、以超声信号检测为物理手段的新型成像方法,它结合了光学成像的高对比度优势和超声成像的高穿透深度特性,成为当今生物医学工程研究领域的热点。如何实现具有高探测精度、高对比度、高空间分辨率的光声成像手段成为该领域研究人员的共同目标。超声信号检测是光声成像技术中的关键技术环节,传统采用压电式传感器进行超声信号探测,其灵敏度相对较低,响应带宽窄,不利于实现高性能成像。与之相比,光纤超声传感器具有较高的探测灵敏度,以及抗电磁干扰的特性。为了实现高灵敏度、高对比度和高空间分辨率的光声成像方法,我们提出采用微纳光纤光栅Fabry-Perot干涉仪进行超声信号探测。与传统光纤超声传感器相比,这一器件是在直径仅为几个微米的光纤上制作的,具有更高的空间分辨率和更好的成像对比度特性。同时,借助微纳光纤的强瞬逝场作用和高反射率的光纤光栅刻写技术,对超声信号的响应灵敏度也显著提升。本文的主要内容包括:微纳光纤光栅Fabry-Perot干涉仪是进行光声成像的物理基础,本文首先对其制备工艺、光谱特性和传感特性进行了研究。该器件是采用193nm准分子激光器在微纳光纤上依次刻写两根光栅而制成的。采用多模光纤进行微纳光纤的拉制,以提升模场与光栅的空间交叠区域,从而解决了成栅效率低下的问题。采用数值模拟方法获得了微纳光纤光栅Fabry-Perot干涉仪的光谱特性,对光纤几何尺寸、光栅反射率等参数对其透射光谱的影响机理进行了分析。通过研究该器件对温度和折射率的响应特性发现,基模和高阶模干涉峰对折射率和温度的灵敏度不同,基于这一特性可以有效去除温度的交叉敏感性问题。利用微纳光纤光栅Fabry-Perot干涉仪进行超声探测是实现光声成像的基础,我们对这种超声传感器的响应机理和增敏方法进行了深入研究。首先,理论分析了这种超声传感器的响应机理,揭示了倏逝场对于这种声传感器灵敏度所起的关键性作用。实验上采用直径为5.2μm的声传感器,实现了超声灵敏度为1.845mV/kPa。在传统单模光纤中采用相同方法制成的声传感器灵敏度仅为0.184mV/kPa,这说明微纳光纤的倏逝场作用使灵敏度提升了10倍。进一步研究了这种声传感器的输出电压功率谱和频率响应谱,测量了超声检测的方向依赖性。提出增强超声灵敏度的两个方法:一是通过增加光纤光栅的反射率,从而提高干涉条纹锐度,另一种是通过减小微纳光纤直径从而增强倏逝场作用。微纳光纤光栅Fabry-Perot干涉型声传感器的研究是实现生物医学光声成像的基础,我们对这种声传感器的响应原理、提高灵敏度的方法以及传感特性进行了深入研究。首先,理论分析推导了这种声传感器的响应机理,揭示了倏逝场对于这种声传感器灵敏度所起的关键性作用。找出了进一步提高灵敏度性能的两个因素:一种是通过增加光纤光栅的反射率从而提高干涉条纹斜率的方法,另一种是通过减少微纳光纤直径从而增加模式折射率变化的方法。其次,实现了采用这种声传感器测量声压的方法,直径为5.2μm的声传感器的灵敏度为1.845mV/kPa。而同样条件下,普通光纤制成的声传感器的灵敏度为0.184mV/kPa,其灵敏度比普通单模光纤的高出10倍。最后,进一步研究了这种声传感器的输出电压功率谱和频率响应谱,验证了微纳光纤光栅Fabry-Perot干涉型声传感器的检测方向特性。基于以上研究,本文采用微纳光纤光栅Fabry-Perot干涉型超声传感器,实现了高灵敏度、高空间分辨率的生物医学光声成像。我们分析了生物组织的基本特性,研究了光声信号的产生条件。然后根据光声信号的声压波动方程对光声信号的机理进行了阐述,同时给出了采用的图像重建方法及其数学推导过程。对成年人体的头发进行了光声成像实验,采用所研制的超声传感器,对由激光诱导的超声信号进行扫描探测,并对测得的信号在扫描柱面上的空间分布重构空间光学吸收的二维分布图像,光声成像的空间分辨率达到了95μm。最后研究了测量位置数对光声成像质量的影响,发现提高测量位置数目能够提高重建图像的质量和空间分辨率,但是二者的关系并不是一个线性的关系。在实际研究中,需要综合考虑成像质量、空间分辨率、扫描速度等因素,提出优化的测量方案。
[Abstract]:Biomedical engineering is an application of the principle and method of natural science and engineering technology, the research of various organisms especially the structure of the human body, and other life science. Biomedical imaging technology is one of the most important parts in the field of Biomedical Engineering, by using optical microscopy, magnetic resonance and other physical means, access to space optical human organization the absorption distribution function, useful information extraction of eyes can not get, provide an important basis for early diagnosis of the disease, is of great significance to human health. Among them, photoacoustic imaging method is based on the photoacoustic effect, a new imaging method in ultrasonic signal detection for physical means, it combines the high penetration characteristics of high contrast the advantages of optical imaging and ultrasound imaging, becoming a hot research topic in the field of biomedical engineering. How to achieve high accuracy, High contrast, high spatial resolution photoacoustic imaging method has become the common goal of researchers in this field. Ultrasonic signal detection is key technology of photoacoustic imaging technology in the traditional piezoelectric sensor for ultrasonic signal detection, the sensitivity is relatively low, the response bandwidth, is not conducive to the realization of high performance imaging. In comparison, the detection sensitivity of ultrasonic sensor is high, and the characteristics of anti electromagnetic interference. In order to achieve high sensitivity photoacoustic imaging method with high contrast and high spatial resolution, we propose the use of micro nano optical fiber grating Fabry-Perot interferometer for ultrasound detection. Compared with the traditional ultrasonic sensor, this device is in the production of fiber diameter of only a few microns on, with higher spatial resolution and better image contrast characteristics. At the same time, with the strong transient micro nano optical fiber evanescent field And the high reflectivity of fiber grating writing technology, the response sensitivity of the ultrasonic signal is significantly improved. The main contents of this paper include: micro nano fiber grating Fabry-Perot interferometer is the physical basis of photoacoustic imaging, firstly the preparation process of the system, spectral properties and sensing properties were studied. The device is used 193nm excimer laser in micro nano optical fiber grating in writing and made two. Using multimode fiber draw micro fiber, overlapping regions to enhance the mode field and grating space, so as to solve the problem of low efficiency into grid. Numerical simulation method is used to obtain the spectral characteristics of micro nano fiber grating Fabry-Perot interferometer. The mechanism of fiber geometry, grating reflectivity parameters influence on the transmission spectra is analyzed. Through the research of the device in response to the temperature and refractive index. Now, the fundamental mode and higher-order mode interference peaks of refractive index and temperature sensitivity, cross sensitivity and it can be effectively removed based on temperature. Using micro nano fiber grating Fabry-Perot interferometer for ultrasound detection is based on photoacoustic imaging, we on the response mechanism of ultrasonic sensor and sensitization method the in-depth study. Firstly, the theoretical analysis of the response mechanism of the ultrasonic sensor, reveals the key role for the evanescent field sensitivity of the acoustic sensor. The experiment using acoustic sensor with diameter of 5.2 m, the sensitivity of ultrasonic acoustic sensor sensitivity 1.845mV/kPa. using the same method in the traditional single-mode fiber made the only 0.184mV/kPa, indicating that the micro nano optical fiber evanescent field sensitivity up to 10 times. Further study of the output voltage power spectrum of the acoustic sensor And the frequency response spectrum, ultrasonic detection direction measurement dependent. Two methods are proposed to enhance the sensitivity of ultrasound: one is by increasing the reflectivity of fiber grating, thereby improving the fringe sharpness, the other is by reducing the diameter of micro nano fiber enhanced evanescent field. Research on micro nano fiber grating interferometric acoustic Fabry-Perot the sensor is based on biomedical photoacoustic imaging principle, our response to the acoustic sensor and method of improving the sensitivity and sensing characteristics were studied. Firstly, the theoretical analysis of the response mechanism of the acoustic sensor, reveals the key role of evanescent field for the sensitivity of the acoustic sensor. Find out two factors to further improve the sensitivity of performance: one is the method of interference fringes by slope increasing reflectivity of fiber grating to improve, the other is through Reducing microfiber diameter increasing method the refractive index change. Secondly, the method of using the measurement of the pressure sensor, a diameter of 5.2 m acoustic sensor sensitivity is 1.845mV/kPa. and under the same conditions, the acoustic sensor sensitivity to 0.184mV/kPa ordinary optical fiber, its sensitivity is 10 times than the ordinary single-mode fiber. Finally, further research on the acoustic sensor output voltage power spectrum and frequency response spectrum, and validate the directional characteristics of micro nano fiber grating Fabry-Perot interferometric acoustic sensor. Based on the above research, this paper adopts the micro nano fiber grating Fabry-Perot interferometric ultrasonic sensor, to achieve high sensitivity, biomedical photoacoustic imaging with high spatial resolution. We analyzed the basic characteristics of biological tissues, on the condition of producing the photoacoustic signal. Then based on photoacoustic signal pressure The mechanism of wave equation on photoacoustic signal are described, and gives the image reconstruction methods and mathematical derivation. The adult body hair of photoacoustic imaging experiment, ultrasonic sensor was developed by the ultrasonic signal by laser induced by scanning probe, and the distribution of two-dimensional image signal measured in the spatial distribution of cylindrical scanning reconstruction of space optical absorption, spatial resolution photoacoustic imaging at 95 M. was also studied to measure the position of the number of photoacoustic imaging quality, improve the measuring position number can be found to improve the quality and spatial resolution of the reconstructed image, but the relationship between the two and the relationship is not a a linear. In the actual research, need to consider the imaging quality, spatial resolution, scanning speed and other factors, the measurement scheme optimization.

【学位授予单位】：暨南大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：R318;TH744.3

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