Laser-pulse-synchronized image acquisition system the optimization of digital and analog circuits

• Main Authors: Jing-Zun Wang, 王靖尊
• Other Authors: Tzu-Ming Liu
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/g529dv

碩士 === 國立臺灣大學 === 醫學工程學研究所 === 104 === The routine human blood test is an important indicator in the evaluation of personal health. Analytical instruments such as flow cytometry are applied to count the numbers of erythrocytes, leukocytes, and platelets, and the numbers all carry their own significance in the differential diagnosis. However, we usually examine blood status by using invasive procedures such as blood sampling, which not only burdens patients, but also lead to the deterioration of the specimens during the delivery process, and may cause errors in health evaluations. With medical technology advances, many experimental non-invasive biomedical imaging technology methods have been developed. By using an interferometer, near infrared light, and the interference principle to image the biological tissue. Optical Coherence Tomography provides two-dimensional tomographic images of in vivo biological tissue with micron grade resolution. By using the pinhole to block unfocused light and the interference of scattering light, confocal microscopy provides biopsy images with sub-micron level resolution, Use of high tissue penetration depth of infrared light, these techniques can get the blood cell imaging in vivo without calibration.. Owing to the restriction of light diffraction limitations and tissue scattering, confocal microscopy cannot provide sub-micron resolution of clear images with tissues in depth; therefore, Lack of ability to identify various types of blood cells. Comparing harmonic generation microscopy to other optical tomographic microscopies, it is characterized by sub-micron three-dimensional resolution with tissues in depth. The research has been verified that can get human flow of blood cell images and interpret of the number of leukocytes in vivo, it is currently the most potential to develop into a non-invasive in vivo imaging flow cytometer technology. In addition, there is also no need to use dye during the examination. When there is any doubt of the percent composition of blood cells with flow cytometry, the patient’s blood specimen should be sent for further blood smear, which is where cells are stained to investigate the blood cell morphology. By using third harmonic generation microscopy (THG), there is no need to stain the blood cells before investigating while in the meantime the images can be saved. This method not only saves the examination time of the blood smear, but also presents the original morphology of the blood cells. To provide a stable light source for third harmonic generation microscopy, a 1150 nm femtosecond fiber laser system was built in our laboratory that is relatively insensitive, with temperature and humidity that are comparable to the Ti-Sapphire laser and Chromium-Doped Forsterite Laser. Four modes of analog signals are provided in the microscopy system, including second harmonic generation microscopy, third harmonic generation microscopy, multi-photon fluorescence microscopy, and confocal single-photon reflection microscopy. Today’s capture board that transform analog to digital cannot process the four types of the signal directly, and there is depletion phenomenon that takes place in the DC signals while transforming between the two signal types, causing a weakening of the signal amplitude. On the part of image capture, the pulse-repetition rate of laser light source is only 11.25 MHz. When shifting the focal point of the laser through fast-steering tilt-axis scan mirrors, (8 kHz) intervals time between points are larger. Thus, it is essential to capture the maximum of the every signal point, and to prevent weaker signal capture, which will cause reductions in image intensity. Therefore, to get high resolution and immediate investigations of the blood cells status, in respect to hardware, the norms of the microscopy system must be compatible with optical signals to preserve the DC signals. With respect to software, the analog signals of the specimens stimulated by the laser must be captured with the help of the synchronization of the laser signals to the get maximum level of analog signal to improve the contrast of the image. In this thesis, we use field-programmable gate array (FPGA) design imaging acquisition system. FPGA not only reduce development time, but also has high efficiency and reliability. By using the Phase-locked loops (PLL) in FPGA, we synchronized the sampling clock with the laser pulse, and designed to meet this FPGA board of the analog to digital converter board (ADCB). In addition, we programmed a graphical user interface with multi-channel 15Hz frame rate windows to display and restore the image. This interface can also be immediate changed FPGA parameters, such as imaging range, sampling clock frequency and laser pulse phase function. At the same time, we also provided another capture mode (XYT mode) for long video-recording that sets the video intervals flexibility. It can save single images or multiple images taken at certain time intervals over an average period, thus reducing the data size of the images saved. It can also provide basic image processing functions. Synchronized the sampling clock with the laser pulse and used our analog to digital converter board, we can clearly observe images of blood cells in mouse ear capillaries, Thereby reducing the difficulty of automated image interpretation. We hope that for future clinical applications, the non-invasive automatic evaluation of speed and number of blood cells using the fiber femtosecond laser microscope system could be faster and more precise using this synchronous acquisition system.