Design And Implementation Of Near-Infrared Brain Tissue Blood Oxygenation Detection System Based On Optical Frequency Division Multiplexing

In recent years,functional near-infrared spectroscopy imaging systems have developed rapidly with the development of biomedicine.It is widely used to detect blood flow changes caused by neural activity in the human brain and to monitor blood oxygen metabolism in the brain.In order to facilitate the study of human blood oxygen signal,this paper designed and developed a near-infrared brain tissue blood oxygen detection system based on optical frequency division multiplexing.Firstly,the hardware circuit of optical frequency division multiplexing near-infrared brain tissue blood oxygen detection system is designed.Aiming at the shortcomings of continuous wave detection system,the working mode of the system is designed.Based on it,NI myDAQ and FPGA are used as the hardware platform of the system.The performance characteristics of the light source are analyzed,and the light source drive circuit and DAC module circuit are designed.And the frequency division multiplexing working mode is selected;the performance of the photodetector is analyzed,the type of photodetector is determined,and then the bandpass filter circuit and the gain amplifying circuit are designed to complete the preprocessing of the signal.Secondly,FPGA and LabVIEW are used to write the software program of near-infrared brain tissue blood oxygen detection system.Based on the hardware circuit,the direct digital frequency synthesizer program is developed with FPGA according to the working mode of frequency division multiplexing.The demodulation principle of the system is analyzed.The orthogonal demodulation program of digital signal is developed with LabVIEW.The MBLL algorithm is designed to solve the problem of the divergence of near-infrared light signals in the tissue,so as to realize the calculation of hemoglobin concentration change.Finally,a near-infrared brain tissue blood oxygenation detection system with optical frequency division multiplexing and dual channel was developed,and its hardware performance test and experimental verification were carried out.The transmission fiber was designed and a plano-convex lens was added at the fiber probe.The performance of the DAC module and the signal processing module is tested,and the feasibility is verified.The reliability of the system was tested and verified by resting state in the forehead tissue and Valsalva human blood oxygenation test.