Development And Verification Of Compact Reflective Near-infrared Diffuse Optical System

In recent years,due to the rapid development of Diffuse Optical Tomography(DOT),this technology has been used in various clinical studies,including breast cancer,functional brain imaging and peripheral arterial disease.The reflective imaging device developed with the help of this imaging technology is flexible in use and has great potential in various clinical applications due to its non-invasive,non-ionizing radiation and low cost characteristics.However,the existing reflective imaging device has a complicated structure and low compactness.The goal of this study is to develop a compact,convenient,and highly sensitive new reflective diffuse optical imaging device.1.Compact design of the front end of the reflective system.Based on the compact design characteristics of the front end of the device,a new type of photodetector(silicon photomultipliers,SiPM)is used as the photodetector in the hardware,and a dual-wavelength light emitting diode(LED)as the source.At the same time,the layout of the source and detector was studied.First,the effective distance range between source and the detector for the reflective system is determined to be 10～63.69mm.Secondly,considering the influence of the density of the layout on the imaging penetration depth within the range of the source detection distance,three reasonable source detection numbers of 4 source 4 detector,8 source 8 detector and 13 source 12 detector and arrange the corresponding simulation experiments.The experimental results are analyzed in terms of imaging depth and hardware implementation difficulty.When the number of sources and detectors is 8,the device is relatively easy to implement and the imaging depth is comparable to the arrangement of 13 sources and 12 detectors.Finally,the effect of the arrangement of 8 sources and 8 detectors on the penetration depth is studied,and the best source detection arrangement-diamond arrangement is obtained.2.The overall hardware implementation and testing of the system.The LED in the source module needs a stable current for normal operation.Therefore,a corresponding LED drive circuit is designed.Aiming at the problem of weak current signal obtained by SiPM photoelectric conversion,the detection module has designed a SiPM readout circuit.In order to realize the miniaturization of the system,the control of the system is realized by using STM32 microcontroller.In terms of hardware,the power supply of the whole system,the switching of 8 dual-wavelength LED,the optical signal reception of SiPM and the data collection are realized by using it.The software part,including the software development of the upper computer and the software development of the lower computer,jointly realizes the source switching and data collection functions.The system performance was tested,and volunteers were called in to conduct cuff blocking experiments.The experimental results verify the effectiveness of the system’s dual wavelength and its ability to quickly track changes in hemodynamics.3.Perform system consistency correction and imaging effect verification.In order to ensure the reliability of the system,the system was tested for the output results affected by temperature.The reason for the deviation of the output results is analyzed,and the output power of the hardware circuit is adjusted.Under the same conditions,the problem of inconsistent output results of each detector channel,the coefficient correction method is used to improve the channel consistency.On this basis,the linearity correction of the output results is made by the method of curve fitting,which makes up for the characteristic of SiPM output nonlinearity.In order to test the imaging performance of the system,this thesis designed phantom experiments with different detection depths.The results show that the reflective imaging device can locate the position of the foreign body,and its effective imaging depth can reach 22.5mm.