时域光学信息在生命科学领域中向来具有重要价值，许多成像方法都依赖时域检测系统提供的信息来作为成像依据。由于荧光寿命不受强度、荧光团浓度和光漂白效应等因素的影响，使得近几十年来面向荧光寿命的时域检测系统不断地进步，衍生出了各种新颖的生物医学应用，并揭示出了许多新的发现。然而，传统的检测系统体积较大，检测方式单一，成本较高，一定程度上限制了其适用性。这些问题使得搭建低成本、小型化、高精确度且性能可靠的系统成为一个十分有意义的课题。

本文主要设计开发了一种面向荧光寿命检测的时域光学检测系统。在经典的时间相关单光子计数技术基础上，系统采用简捷高效的全数字时间数字转换器（TDC）替代复杂的模拟时间数字转换器（TAC/ADC）结构。在满足单光子检测灵敏度的情况下，用小体积且低成本的硅光电倍增管（SiPM）替代大尺寸且高成本的光电倍增管（PMT）作为探测器，构建紧凑、高性价比的检测系统。主要工作分为以下几个方面：

1、时间数字转换器的研究及设计实现。从基本的时间间隔测量原理出发，研究了模拟TDC和数字TDC的演变过程，TDC核心参数，以及典型TDC实现原理。并且基于时钟内插法原理，分别在Altera CycloneIV和Xilinx Kintex7系列现场可编程门阵列（FPGA）上自主设计开发了全数字TDC，对于后者通过优化设计解决了延迟链跨时钟区域时出现的延迟时间跳变问题。开发完成的两种TDC都经过了核心参数的测试，在Altera CycloneIV和Xilinx Kintex7上分别实现了87.72 ps和42.55 ps的时间分辨率，平均精度分别达到41.8ps和37.1ps，动态范围可以根据需求自由调整，非线性程度处于可以接受的水平，并通过后期矫正算法来优化。

2、单光子探测模块的设计与实现。针对传统单光子探测器体积大、成本高的问题，通过测试分析了PM3325和H7422-40在进行单光子计数时的信号特点，验证了SiPM可以在应用中替代PMT。并且针对已经实现的检测系统进行了紧凑型设计，将探测器模块集成在一块80mm×93mm大小的PCB电路中，添加了配合FPGA使用易用性设计，此外还通过峰值检波法优化了比较器电路，在提升系统性能的同时实现了小型化与低成本化。

3、荧光寿命检测系统的搭建与实验验证。整合搭建完整的荧光寿命检测系统，通过测试验证了其功能，并展开了荧光寿命检测实验。实验测试了吲哚菁绿（ICG）的荧光寿命，测试结果为0.54ns，与真实结果相差约3.8%。

The time-domain optical information has always been of great value in the field of life science. Many imaging methods rely on the information provided by the time-domain detection system as the imaging basis. Because fluorescence lifetime is not affected by intensity, fluorophore concentration and light bleaching effect, the time-domain detection system oriented to fluorescence lifetime has been developed continuously in recent decades, resulting in a variety of novel biomedical applications and many new discoveries. However, the large size, single detection method and high cost of the traditional detection system limit its applicability to a certain extent. These problems make the construction of low cost, small, high accuracy and reliable performance system become a very meaningful topic.

 

This thesis mainly designs and develops a time-domain optical detection system for fluorescence lifetime detection. Based on the classical time-dependent single photon counting technique, the system uses a simple and efficient all-digital TDC to replace the complex traditional TAC/ADC structure. Under the condition that the sensitivity of single photon detection is satisfied, the compact and low-cost detection system is constructed by replacing the large size and high cost PMT detector with a small size and low cost SiPM array. The main work is divided into the following aspects:

 

1. Research, design and implementation of time digital converter. Based on the basic time interval measurement principle, the evolution process of analog TDC and digital TDC, the core parameters of TDC, and the typical implementation principle of TDC are studied. Moreover, based on the principle of clock interpolation, an all-digital TDC was independently designed and developed on Altera CycloneIV and Xilinx Kintex7 series FPGA respectively. For the latter, the problem of delay time hopping occurred when the delay chain crossed the clock region was solved through optimization design. The two developed TDCS have been tested on the core parameters. The time resolution of 87.72ps and 42.55ps has been achieved on Altera CycloneIV and Xilinx Kintex7, and the average accuracy has reached 41.8ps and 37.1ps, respectively. The dynamic range can be adjusted freely according to the demand, the degree of nonlinearity is at an acceptable level, and is optimized by the late correction algorithm.

 

2. Design and implementation of single photon detection module. Aiming at the problems of large volume and high cost of traditional single photon detectors, the signal characteristics of PM3325 and H7422-40 in single photon counting were analyzed through testing, and SiPM could replace PMT in application. The detector module is integrated into an 80mm×93mm PCB circuit, and the design of ease of use with FPGA is added. In addition, the peak detection method is used to optimize the comparator circuit, which not only improves the system performance but also realizes miniaturization and low cost.

 

Establishment and experimental verification of fluorescence lifetime detection system. Integrated and built a complete fluorescence lifetime detection system, its function was verified by testing, and the fluorescence lifetime detection experiment was carried out. The fluorescence lifetime of indocyanine green (ICG) was measured by experiment, and the result was 0.54ns, which was 3.8% different from the real result.

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