【作者】 姜润华；

【导师】 曾绍群；

【作者基本信息】 华中科技大学 ， 生物医学工程， 2012， 博士

【摘要】 神经元网络的结构和功能研究对了解大脑的信息处理和整合机制具有非常重要的意义。双光子显微成像技术具有空间分辨率高、成像深度大以及光损伤小等优点,有望为神经元网络研究提供一种重要的研究手段。为了监测神经元网络毫秒级的快速功能信号,需要进一步提高双光子显微成像技术的时间分辨率。声光偏转器作为一种光束扫描器件,扫描过程中不引入机械惯性,具有快速光栅式扫描和随机点扫描等多样性的扫描模式,近年来成为发展快速双光子显微成像技术的一种非常受欢迎的器件。相比于常规的检流计镜扫描,声光偏转器可实现的扫描范围较小,导致双光子显微镜的扫描视场较小,因而限制了对更大神经元网络的研究。本文从增大声光偏转器自身带宽的角度来扩大系统的扫描范围,以获得大视场的双光子显微成像系统。因此,本文围绕发展用于光子显微镜的宽带声光偏转器,从声光偏转器的热效应分析、宽带声光偏转器的设计实现以及基于宽带声光偏转器构建大视场双光子显微成像系统三个部分展开研究。(1)分析了声光偏转器的热源,分别研究了超声吸收和换能器发热两部分热源发热功率的计算方法。基于有限元分析软件,建立了声光偏转器热效应的数值分析模型,获得了声光偏转器空间温度分布及随时间变化的温度曲线的仿真结果,并用实验测量结果对仿真结果进行验证,证实了仿真模型的有效性。利用此仿真模型,可以方便地模拟各种复杂的器件结构,评估不同散热措施对应的声光偏转器热效应,这对于指导大功率声光偏转器的热设计是十分有用的。(2)通过改进声光偏转器的设计参数,设计实现了波长为840 nm,适用于双光子显微成像的宽带声光偏转器。实验测试结果表明,新器件的3 dB带宽可以达到60MHz,衍射效率为40%-80%,扫描角度范围从原来的47 mrad提高到了74 mrad。为了降低声光晶体对超声的吸收,新器件的工作频率全部低于100 MHz,频带设计打破了商品化器件普遍遵循的一倍频程原则,实践证明这种设计方法是可行的。(3)基于以上定制的宽带声光偏转器,搭建了大视场的双光子显微成像系统。从色散补偿、系统光路、硬件和软件控制几部分进行研究,最后测试了系统所达到的成像性能。系统全场的空间分辨率为横向：0.58-2.12μm和纵向：2.17-3.07μm。在没有牺牲空间分辨率的前提下,系统总的扫描角度达到了93 mrad(即5.3°),满足了显微物镜5-6°的可接受入射角要求。40倍物镜下系统的视场可以达到418μm,是常规的基于声光偏转器的双光子显微镜视场的两倍以上,为神经元网络的结构和功能研究提供了一个新的研究平台。更多还原

【Abstract】 The research on the structure and function of neuronal networks is extremely important for understanding brain’s information processing and integration mechanism. Two-photon microscopy (TPM) has the potential to become an important tool for neuronal networks’research, due to its advantages of high spatial resolution, deep penetration, and low photodamage. In order to detect the fast functional signal of neuronal networks at millisecond scale, the temporal resolution of TPM needs to be increased. In recent years, acousto-optic deflector (AOD) has become a popular beam scanner in developing fast scanning TPM, because the acousto-optic scanning does not involve mechanical inertia and can provide versatile scanning modes, such as fast raster scanning and random-access point scanning. Compared with the conventional galvanometer scanner, the scanning range of AOD is smaller, which leads to a small field of view (FOV) of TPM and therefore limits its applications in large neuronal networks. In order to obtain a two-photon microscope with large FOV, the frequency bandwidth will be widened to enlarge the system’s scanning range in this thesis. Therefore, this study focuses on the development of wide-band AOD for TPM, and mainly includes three parts:the establishment of the thermal analysis method for AOD, the design and realization of wide-band AOD, and the construction of large FOV TPM based on wide-band AOD.(1) The thermal sources of AOD is analyzed which includes acoustic absorption and transducer heating. The methods of calculating heating power of both thermal sources are studied. Based on the finite element analysis (FEA) software, a numerical analyzing model for the thermal effects analysis is built. The spatial temperature distributions in the crystal and the temperature changes over time are acquired. The simulation results are validated by experimental results. Using this model, the device with more complicated structure can be simulated conveniently. The AOD’s thermal performance in different heat dissipation schemes can be evaluated, which would be helpful in guiding the thermal design of high-power AOD.(2) Wide-band AOD is custom designed by means of improving the device’s technical parameters. The new AOD works at 840 nm wavelength which is suitable for TPM. The experimental test results indicate that the 3- dB bandwidth of the new device reaches 60 MHz, and the diffraction efficiency is between 40% and 80%. The scan range increases to 74 mrad from the previous 47 mrad. All the operating frequencies are designed to be lower than 100 MHz to decrease the acoustic absorption. Unlike the commercial products, the bandwidth design in this study does not obey the one-octave principle, which has been proved to be feasible in the practice.(3) A TPM system based on the two-dimensional wide-band AODs is built. The research consists of the dispersion compensation, the systematic optical path, the hardware control, and software control. The imaging performances of the system are measured. The spatial resolution across the whole FOV is 0.58-2.12μm laterally and 2.17-3.07μm axially. The total scan range of the system reaches 93 mrad (5.3°), which can basically meet the requirement of 5-6°for most objectives. The FOV is 418μm under 40 X objective, which is more than twice as much as that based on conventional AODs. The AOD-based large FOV two-photon microscope could provide a new platfonn for researches on the structure and function of neural circuits.更多还原