Development Of Hemoglobin Concentration Measurement System Based On High Frequency Modulation And Frequency Domain Heterodyne

In recent years,functional near-infrared spectroscopy imaging systems have developed rapidly with the development of biomedicine,which is of great significance for in-depth study of blood flow changes caused by neural activities in the human brain and monitoring of brain blood oxygen metabolism.The ability to quantitatively measure the absolute value of the hemoglobin concentration of human tissues has become a key issue that needs to be resolved.In order to solve this key problem,this paper designed and developed a set of hemoglobin concentration measurement system based on high frequency modulation and frequency domain heterodyne.First,the infinite medium diffusion model and the overall structure of the system are established.In order to obtain the propagation information of photons in biological tissues and the optical parameters of tissues,theoretical analysis was carried out on the Boltzmann transport equation,the photon diffusion equation in biological tissues and the approximate model of infinite medium diffusion were established,and the optical parameters and tissue physiology were determined.The relationship of the parameters: For the measurement of the optical parameters of the organization,the working principle and working mode of the system are analyzed and clarified,the types of the system’s light source and light detector are determined,and the overall structure of the system is established.Secondly,the hardware circuit of the hemoglobin concentration measurement system based on high frequency modulation and frequency domain heterodyne is designed and implemented.In order to achieve high-frequency modulation of the light source,a driving method that uses a DC current source and a high-frequency current source to drive the light source is designed and the light source drive circuit is designed;for the phase measurement of the light emitted by the tissue,an external photomultiplier tube is designed.Difference detection circuit,and designed current-voltage conversion circuit and filter circuit according to the signal characteristics of the photodetector,and completed the signal preprocessing.Finally,a hemoglobin concentration measurement system based on high frequency modulation and frequency domain heterodyne was built,and its performance test and experimental verification were carried out.In view of the realization of the system’s working mode and the use of optical parameters for the calculation of the absolute value of hemoglobin concentration,the software program of the system was designed and written;in order to verify the feasibility of the system,the performance test of the light emitting and light receiving modules was performed;The resting state and Valsalva human hemoglobin concentration measurement experiments were carried out to detect and verify the reliability of the system.