【作者】 侯少华；

【导师】 赵会娟；

【作者基本信息】 天津大学 ， 光学工程， 2010， 硕士

【摘要】 DOT(Diffuse Optical Tomography)依靠扩散光在组织中较深的穿透深度实现器官级的诊断层析成像,能提供组织体的解剖和生理功能信息,以其无创性、安全性等优点在乳腺成像、新生儿大脑供氧状况及血氧动力学观测等方面得到了广泛应用。连续光DOT的图像重建算法需要测量多点分别激励下表面各点的光流输出分布,因此需要对光源进行编码。目前使用最多的是基于光开关的时分复用技术,这种方法需要将光源分时依次导入不同位置的入射光纤,当源的位置较多或使用多波长测量时,测量时间会因此变的很长,且同一测量周期内不同位置的测量间隔也较长,这非常不利于需要捕捉变化信号的动态成像应用,如脑功能成像。频分复用的源编码技术可以解决这个问题,它使用不同频率的正弦波调制多个光源,并将这些光源同时入射到成像腔,在探测端使用数字锁相检测技术可以从混合的信号中将各个光源对应的出射光信息分别求得。这种方法大大加快了DOT系统的测量速度,并且能够同时获取不同源-探测器位置的多个测量值,其成像结果更加真实的反映客观现象。本文研究了数字锁相检测技术在基于光子计数的稳态DOT系统中的应用,以FPGA为平台实现了用于光子计数测量系统的数字锁相检测装置,初步建立了一个双通道光子计数DOT实验系统,主要包括两个可调制连续激光器、光子计数探测器、数字锁相检测与控制电路,并编写计算机程序进行控制和显示。最后通过一系列测量实验对该实验系统进行评估和分析,总结成果和不足,并对下一步的研究进行展望。更多还原

【Abstract】 Relying on deeper penetration of light in the tissue,DOT(Diffuse Optical Tomography)achieves organ-level tomography diagnosis, which can provide information on anatomical and physiological features. DOT has been widely used in imaging of breast, neonatal cerebral oxygen status and blood oxygen kinetics observed by its non-invasive, security and other advantages.Continuous wave DOT image reconstruction algorithms need the measurement of the surface distribution of the output photon flow inspired by more than one driving source, which means that source coding is necessary. Most currently used source coding in DOT is time-division multiplexing technology, which utilizes the optical switch to switch light into optical fiber of different locations. In case of large amounts of the source locations or using the multi-wavelength, the measurement time and the measurement interval between different locations within the same measurement period will therefore become too long to capture the dynamic changes in real-time imaging applications, such as brain imaging. Frequency division multiplexing source coding technology can solve this problem. It uses several light sources modulated by different frequency sine wave incident to the imaging chamber simultaneously. Signal corresponding to the various sources are obtained from the mixed output light using digital phase-locked detection technology in the detection end. This method greatly accelerates the DOT system measurement, and can also obtain the multiple measurements in different source-detector locations. The imaging results reflect the objective phenomenon more accurately.This paper studies the digital lock-in detection technology in continuous wave DOT imaging system based on photon counting. A digital lock in detection circuit for photon counting measurement system is implemented in a FPGA development platform. A dual-channel DOT photon counting experimental system is preliminary established, including the two continuous lasers, photon counting detectors, digital lock in detection, control circuit, and computer programs to control and display. A series of experimental measurements is taken to validate the feasibility of the system. Finally, the paper summarizes the results and shortcomings, and prospects for future research.更多还原